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How to Cite Sources

Here is a complete list for how to cite sources. Most of these guides present citation guidance and examples in MLA, APA, and Chicago.

If you’re looking for general information on MLA or APA citations , the EasyBib Writing Center was designed for you! It has articles on what’s needed in an MLA in-text citation , how to format an APA paper, what an MLA annotated bibliography is, making an MLA works cited page, and much more!

MLA Format Citation Examples

The Modern Language Association created the MLA Style, currently in its 9th edition, to provide researchers with guidelines for writing and documenting scholarly borrowings.  Most often used in the humanities, MLA style (or MLA format ) has been adopted and used by numerous other disciplines, in multiple parts of the world.

MLA provides standard rules to follow so that most research papers are formatted in a similar manner. This makes it easier for readers to comprehend the information. The MLA in-text citation guidelines, MLA works cited standards, and MLA annotated bibliography instructions provide scholars with the information they need to properly cite sources in their research papers, articles, and assignments.

• Book Chapter
• Conference Paper
• Documentary
• Encyclopedia
• Google Images
• Kindle Book
• Memorial Inscription
• Museum Exhibit
• Painting or Artwork
• PowerPoint Presentation
• Sheet Music
• Thesis or Dissertation
• YouTube Video

APA Format Citation Examples

The American Psychological Association created the APA citation style in 1929 as a way to help psychologists, anthropologists, and even business managers establish one common way to cite sources and present content.

APA is used when citing sources for academic articles such as journals, and is intended to help readers better comprehend content, and to avoid language bias wherever possible. The APA style (or APA format ) is now in its 7th edition, and provides citation style guides for virtually any type of resource.

Chicago Style Citation Examples

The Chicago/Turabian style of citing sources is generally used when citing sources for humanities papers, and is best known for its requirement that writers place bibliographic citations at the bottom of a page (in Chicago-format footnotes ) or at the end of a paper (endnotes).

The Turabian and Chicago citation styles are almost identical, but the Turabian style is geared towards student published papers such as theses and dissertations, while the Chicago style provides guidelines for all types of publications. This is why you’ll commonly see Chicago style and Turabian style presented together. The Chicago Manual of Style is currently in its 17th edition, and Turabian’s A Manual for Writers of Research Papers, Theses, and Dissertations is in its 8th edition.

Citing Specific Sources or Events

• Declaration of Independence
• Gettysburg Address
• Martin Luther King Jr. Speech
• President Obama’s Farewell Address
• President Trump’s Inauguration Speech
• White House Press Briefing

Additional FAQs

• Citing Archived Contributors
• Citing a Blog
• Citing a Book Chapter
• Citing a Source in a Foreign Language
• Citing an Image
• Citing a Song
• Citing Special Contributors
• Citing a Translated Article
• Citing a Tweet

6 Interesting Citation Facts

The world of citations may seem cut and dry, but there’s more to them than just specific capitalization rules, MLA in-text citations , and other formatting specifications. Citations have been helping researches document their sources for hundreds of years, and are a great way to learn more about a particular subject area.

Ever wonder what sets all the different styles apart, or how they came to be in the first place? Read on for some interesting facts about citations!

1. There are Over 7,000 Different Citation Styles

You may be familiar with MLA and APA citation styles, but there are actually thousands of citation styles used for all different academic disciplines all across the world. Deciding which one to use can be difficult, so be sure to ask you instructor which one you should be using for your next paper.

2. Some Citation Styles are Named After People

While a majority of citation styles are named for the specific organizations that publish them (i.e. APA is published by the American Psychological Association, and MLA format is named for the Modern Language Association), some are actually named after individuals. The most well-known example of this is perhaps Turabian style, named for Kate L. Turabian, an American educator and writer. She developed this style as a condensed version of the Chicago Manual of Style in order to present a more concise set of rules to students.

3. There are Some Really Specific and Uniquely Named Citation Styles

How specific can citation styles get? The answer is very. For example, the “Flavour and Fragrance Journal” style is based on a bimonthly, peer-reviewed scientific journal published since 1985 by John Wiley & Sons. It publishes original research articles, reviews and special reports on all aspects of flavor and fragrance. Another example is “Nordic Pulp and Paper Research,” a style used by an international scientific magazine covering science and technology for the areas of wood or bio-mass constituents.

4. More citations were created on  EasyBib.com  in the first quarter of 2018 than there are people in California.

The US Census Bureau estimates that approximately 39.5 million people live in the state of California. Meanwhile, about 43 million citations were made on EasyBib from January to March of 2018. That’s a lot of citations.

5. “Citations” is a Word With a Long History

The word “citations” can be traced back literally thousands of years to the Latin word “citare” meaning “to summon, urge, call; put in sudden motion, call forward; rouse, excite.” The word then took on its more modern meaning and relevance to writing papers in the 1600s, where it became known as the “act of citing or quoting a passage from a book, etc.”

6. Citation Styles are Always Changing

The concept of citations always stays the same. It is a means of preventing plagiarism and demonstrating where you relied on outside sources. The specific style rules, however, can and do change regularly. For example, in 2018 alone, 46 new citation styles were introduced , and 106 updates were made to exiting styles. At EasyBib, we are always on the lookout for ways to improve our styles and opportunities to add new ones to our list.

Why Citations Matter

Here are the ways accurate citations can help your students achieve academic success, and how you can answer the dreaded question, “why should I cite my sources?”

They Give Credit to the Right People

Citing their sources makes sure that the reader can differentiate the student’s original thoughts from those of other researchers. Not only does this make sure that the sources they use receive proper credit for their work, it ensures that the student receives deserved recognition for their unique contributions to the topic. Whether the student is citing in MLA format , APA format , or any other style, citations serve as a natural way to place a student’s work in the broader context of the subject area, and serve as an easy way to gauge their commitment to the project.

They Provide Hard Evidence of Ideas

Having many citations from a wide variety of sources related to their idea means that the student is working on a well-researched and respected subject. Citing sources that back up their claim creates room for fact-checking and further research . And, if they can cite a few sources that have the converse opinion or idea, and then demonstrate to the reader why they believe that that viewpoint is wrong by again citing credible sources, the student is well on their way to winning over the reader and cementing their point of view.

They Promote Originality and Prevent Plagiarism

The point of research projects is not to regurgitate information that can already be found elsewhere. We have Google for that! What the student’s project should aim to do is promote an original idea or a spin on an existing idea, and use reliable sources to promote that idea. Copying or directly referencing a source without proper citation can lead to not only a poor grade, but accusations of academic dishonesty. By citing their sources regularly and accurately, students can easily avoid the trap of plagiarism , and promote further research on their topic.

They Create Better Researchers

By researching sources to back up and promote their ideas, students are becoming better researchers without even knowing it! Each time a new source is read or researched, the student is becoming more engaged with the project and is developing a deeper understanding of the subject area. Proper citations demonstrate a breadth of the student’s reading and dedication to the project itself. By creating citations, students are compelled to make connections between their sources and discern research patterns. Each time they complete this process, they are helping themselves become better researchers and writers overall.

When is the Right Time to Start Making Citations?

Make in-text/parenthetical citations as you need them.

As you are writing your paper, be sure to include references within the text that correspond with references in a works cited or bibliography. These are usually called in-text citations or parenthetical citations in MLA and APA formats. The most effective time to complete these is directly after you have made your reference to another source. For instance, after writing the line from Charles Dickens’ A Tale of Two Cities : “It was the best of times, it was the worst of times…,” you would include a citation like this (depending on your chosen citation style):

(Dickens 11).

This signals to the reader that you have referenced an outside source. What’s great about this system is that the in-text citations serve as a natural list for all of the citations you have made in your paper, which will make completing the works cited page a whole lot easier. After you are done writing, all that will be left for you to do is scan your paper for these references, and then build a works cited page that includes a citation for each one.

Need help creating an MLA works cited page ? Try the MLA format generator on EasyBib.com! We also have a guide on how to format an APA reference page .

2. Understand the General Formatting Rules of Your Citation Style Before You Start Writing

While reading up on paper formatting may not sound exciting, being aware of how your paper should look early on in the paper writing process is super important. Citation styles can dictate more than just the appearance of the citations themselves, but rather can impact the layout of your paper as a whole, with specific guidelines concerning margin width, title treatment, and even font size and spacing. Knowing how to organize your paper before you start writing will ensure that you do not receive a low grade for something as trivial as forgetting a hanging indent.

Don’t know where to start? Here’s a formatting guide on APA format .

3. Double-check All of Your Outside Sources for Relevance and Trustworthiness First

Collecting outside sources that support your research and specific topic is a critical step in writing an effective paper. But before you run to the library and grab the first 20 books you can lay your hands on, keep in mind that selecting a source to include in your paper should not be taken lightly. Before you proceed with using it to backup your ideas, run a quick Internet search for it and see if other scholars in your field have written about it as well. Check to see if there are book reviews about it or peer accolades. If you spot something that seems off to you, you may want to consider leaving it out of your work. Doing this before your start making citations can save you a ton of time in the long run.

Finished with your paper? It may be time to run it through a grammar and plagiarism checker , like the one offered by EasyBib Plus. If you’re just looking to brush up on the basics, our grammar guides  are ready anytime you are.

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Citation Basics

Harvard Referencing

Plagiarism Basics

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• Referencing

A Quick Guide to Referencing | Cite Your Sources Correctly

Referencing means acknowledging the sources you have used in your writing. Including references helps you support your claims and ensures that you avoid plagiarism .

There are many referencing styles, but they usually consist of two things:

• A citation wherever you refer to a source in your text.
• A reference list or bibliography at the end listing full details of all your sources.

The most common method of referencing in UK universities is Harvard style , which uses author-date citations in the text. Our free Harvard Reference Generator automatically creates accurate references in this style.

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Table of contents

Referencing styles, citing your sources with in-text citations, creating your reference list or bibliography, harvard referencing examples, frequently asked questions about referencing.

Each referencing style has different rules for presenting source information. For in-text citations, some use footnotes or endnotes , while others include the author’s surname and date of publication in brackets in the text.

The reference list or bibliography is presented differently in each style, with different rules for things like capitalisation, italics, and quotation marks in references.

Your university will usually tell you which referencing style to use; they may even have their own unique style. Always follow your university’s guidelines, and ask your tutor if you are unsure. The most common styles are summarised below.

Harvard referencing, the most commonly used style at UK universities, uses author–date in-text citations corresponding to an alphabetical bibliography or reference list at the end.

Harvard Referencing Guide

Vancouver referencing, used in biomedicine and other sciences, uses reference numbers in the text corresponding to a numbered reference list at the end.

Vancouver Referencing Guide

APA referencing, used in the social and behavioural sciences, uses author–date in-text citations corresponding to an alphabetical reference list at the end.

APA Referencing Guide APA Reference Generator

MHRA referencing, used in the humanities, uses footnotes in the text with source information, in addition to an alphabetised bibliography at the end.

MHRA Referencing Guide

OSCOLA referencing, used in law, uses footnotes in the text with source information, and an alphabetical bibliography at the end in longer texts.

OSCOLA Referencing Guide

Prevent plagiarism, run a free check.

In-text citations should be used whenever you quote, paraphrase, or refer to information from a source (e.g. a book, article, image, website, or video).

Quoting and paraphrasing

Quoting is when you directly copy some text from a source and enclose it in quotation marks to indicate that it is not your own writing.

Paraphrasing is when you rephrase the original source into your own words. In this case, you don’t use quotation marks, but you still need to include a citation.

In most referencing styles, page numbers are included when you’re quoting or paraphrasing a particular passage. If you are referring to the text as a whole, no page number is needed.

In-text citations

In-text citations are quick references to your sources. In Harvard referencing, you use the author’s surname and the date of publication in brackets.

Up to three authors are included in a Harvard in-text citation. If the source has more than three authors, include the first author followed by ‘ et al. ‘

The point of these citations is to direct your reader to the alphabetised reference list, where you give full information about each source. For example, to find the source cited above, the reader would look under ‘J’ in your reference list to find the title and publication details of the source.

Placement of in-text citations

In-text citations should be placed directly after the quotation or information they refer to, usually before a comma or full stop. If a sentence is supported by multiple sources, you can combine them in one set of brackets, separated by a semicolon.

If you mention the author’s name in the text already, you don’t include it in the citation, and you can place the citation immediately after the name.

• Another researcher warns that the results of this method are ‘inconsistent’ (Singh, 2018, p. 13) .
• Previous research has frequently illustrated the pitfalls of this method (Singh, 2018; Jones, 2016) .
• Singh (2018, p. 13) warns that the results of this method are ‘inconsistent’.

The terms ‘bibliography’ and ‘reference list’ are sometimes used interchangeably. Both refer to a list that contains full information on all the sources cited in your text. Sometimes ‘bibliography’ is used to mean a more extensive list, also containing sources that you consulted but did not cite in the text.

A reference list or bibliography is usually mandatory, since in-text citations typically don’t provide full source information. For styles that already include full source information in footnotes (e.g. OSCOLA and Chicago Style ), the bibliography is optional, although your university may still require you to include one.

Format of the reference list

Reference lists are usually alphabetised by authors’ last names. Each entry in the list appears on a new line, and a hanging indent is applied if an entry extends onto multiple lines.

Different source information is included for different source types. Each style provides detailed guidelines for exactly what information should be included and how it should be presented.

Below are some examples of reference list entries for common source types in Harvard style.

• Chapter of a book
• Journal article

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Your university should tell you which referencing style to follow. If you’re unsure, check with a supervisor. Commonly used styles include:

• Harvard referencing , the most commonly used style in UK universities.
• MHRA , used in humanities subjects.
• APA , used in the social sciences.
• Vancouver , used in biomedicine.
• OSCOLA , used in law.

Your university may have its own referencing style guide.

If you are allowed to choose which style to follow, we recommend Harvard referencing, as it is a straightforward and widely used style.

References should be included in your text whenever you use words, ideas, or information from a source. A source can be anything from a book or journal article to a website or YouTube video.

If you don’t acknowledge your sources, you can get in trouble for plagiarism .

To avoid plagiarism , always include a reference when you use words, ideas or information from a source. This shows that you are not trying to pass the work of others off as your own.

You must also properly quote or paraphrase the source. If you’re not sure whether you’ve done this correctly, you can use the Scribbr Plagiarism Checker to find and correct any mistakes.

Harvard referencing uses an author–date system. Sources are cited by the author’s last name and the publication year in brackets. Each Harvard in-text citation corresponds to an entry in the alphabetised reference list at the end of the paper.

Vancouver referencing uses a numerical system. Sources are cited by a number in parentheses or superscript. Each number corresponds to a full reference at the end of the paper.

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Citing sources: Overview

• Citation style guides

Manage your references

Use these tools to help you organize and cite your references:

• Citation Management and Writing Tools

If you have questions after consulting this guide about how to cite, please contact your advisor/professor or the writing and communication center .

Why citing is important

It's important to cite sources you used in your research for several reasons:

• To show your reader you've done proper research by listing sources you used to get your information
• To be a responsible scholar by giving credit to other researchers and acknowledging their ideas
• To avoid plagiarism by quoting words and ideas used by other authors
• To allow your reader to track down the sources you used by citing them accurately in your paper by way of footnotes, a bibliography or reference list

About citations

Citing a source means that you show, within the body of your text, that you took words, ideas, figures, images, etc. from another place.

Citations are a short way to uniquely identify a published work (e.g. book, article, chapter, web site).  They are found in bibliographies and reference lists and are also collected in article and book databases.

Citations consist of standard elements, and contain all the information necessary to identify and track down publications, including:

• author name(s)
• titles of books, articles, and journals
• date of publication
• page numbers
• volume and issue numbers (for articles)

Citations may look different, depending on what is being cited and which style was used to create them. Choose an appropriate style guide for your needs.  Here is an example of an article citation using four different citation styles.  Notice the common elements as mentioned above:

Author - R. Langer

Article Title - New Methods of Drug Delivery

Source Title - Science

Volume and issue - Vol 249, issue 4976

Publication Date - 1990

Page numbers - 1527-1533

American Chemical Society (ACS) style:

Langer, R. New Methods of Drug Delivery. Science 1990 , 249 , 1527-1533.

IEEE Style:

R. Langer, " New Methods of Drug Delivery," Science , vol. 249 , pp. 1527-1533 , SEP 28, 1990 .

American Psychological Association   (APA) style:

Langer, R. (1990) . New methods of drug delivery. Science , 249 (4976), 1527-1533.

Modern Language Association (MLA) style:

Langer, R. " New Methods of Drug Delivery." Science 249.4976 (1990) : 1527-33.

What to cite

You must cite:

• Facts, figures, ideas, or other information that is not common knowledge

Publications that must be cited include:  books, book chapters, articles, web pages, theses, etc.

Another person's exact words should be quoted and cited to show proper credit 

When in doubt, be safe and cite your source!

Avoiding plagiarism

Plagiarism occurs when you borrow another's words (or ideas) and do not acknowledge that you have done so. In this culture, we consider our words and ideas intellectual property; like a car or any other possession, we believe our words belong to us and cannot be used without our permission.

Plagiarism is a very serious offense. If it is found that you have plagiarized -- deliberately or inadvertently -- you may face serious consequences. In some instances, plagiarism has meant that students have had to leave the institutions where they were studying.

The best way to avoid plagiarism is to cite your sources - both within the body of your paper and in a bibliography of sources you used at the end of your paper.

Some useful links about plagiarism:

• MIT Academic Integrity Overview on citing sources and avoiding plagiarism at MIT.
• Avoiding Plagiarism From the MIT Writing and Communication Center.
• Plagiarism: What It is and How to Recognize and Avoid It From Indiana University's Writing Tutorial Services.
• Plagiarism- Overview A resource from Purdue University.
• Next: Citation style guides >>
• Last Updated: Jan 16, 2024 7:02 AM
• URL: https://libguides.mit.edu/citing

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Harvard Guide to Using Sources 

• The Honor Code
• Citing Sources

Citations provide information to help your audience locate the sources you consulted when writing a paper or preparing a presentation. Some of your instructors will specify which citation format you should use; others will tell you to choose your own citation format as long as you use it consistently. The most common citation formats are MLA (Modern Language Association) style, which is primarily used for papers in the humanities; APA (American Psychological Association) style, which is primarily used for papers in the social sciences; and Chicago style (The Chicago Manual of Style), which is used for both humanities and social science papers.

Some of your courses at Harvard will require you to use other citation formats. Some science courses may require you to use the citation style of the American Medical Association (AMA). AMA style is considered a standard citation format for academic writing in the sciences and is used in many textbooks and medical journals. The AMA Manual of Style is available online . The American Chemical Society publishes its own style guide , which you may be asked to use in chemistry courses. The Harvard Department of Economics provides students with a departmental style guide, which you can find  here . If you are not sure which format to use for a specific course, consult your instructor.

Both APA and MLA styles require you to credit your sources in two ways. First, you must include a parenthetical citation in the text of your paper that indicates the source of a particular quotation, paraphrased statement or idea, or fact; second, you must include a list of references at the end of your paper that enables readers to locate the sources you have used. You can read more about MLA style here and APA style here .

Chicago style also requires you to credit your sources both in the text and at the end of your paper. Chicago offers guidance on two types of in-text citations–notes or parenthetical citations. You can read more about Chicago style here .

If you have questions about which citation style to use, you should always check with your instructor.

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University Library

Start your research.

• Research Process
• Find Background Info
• Find Sources through the Library
• Evaluate Your Info
• Cite Your Sources
• Evaluate, Write & Cite

• is the right thing to do  to give credit to those who had the idea
• shows that you have read and understand  what experts have had to say about your topic
• helps people find the sources  that you used in case they want to read more about the topic
• provides   evidence  for your arguments
• is professional and  standard practice   for students and scholars

What is a Citation?

A citation identifies for the reader the original source for an idea, information, or image that is referred to in a work.

• In the body of a paper, the  in-text citation  acknowledges the source of information used.
• At the end of a paper, the citations are compiled on a  References  or  Works Cited  list. A basic citation includes the author, title, and publication information of the source. 

From:  Lemieux  Library,  University  of Seattle 

Why Should You Cite?

Quoting Are you quoting two or more consecutive words from a source? Then the original source should be cited and the words or phrase placed in quotes. 

Paraphrasing If an idea or information comes from another source,  even if you put it in your own words , you still need to credit the source.  General vs. Unfamiliar Knowledge You do not need to cite material which is accepted common knowledge. If in doubt whether your information is common knowledge or not, cite it. Formats We usually think of books and articles. However, if you use material from web sites, films, music, graphs, tables, etc. you'll also need to cite these as well.

Plagiarism is presenting the words or ideas of someone else as your own without proper acknowledgment of the source. When you work on a research paper and use supporting material from works by others, it's okay to quote people and use their ideas, but you do need to correctly credit them. Even when you summarize or paraphrase information found in books, articles, or Web pages, you must acknowledge the original author.

Citation Style Help

Helpful links:

• MLA ,  Works Cited : A Quick Guide (a template of core elements)
• CSE  (Council of Science Editors)

For additional writing resources specific to styles listed here visit the  Purdue OWL Writing Lab

Citation and Bibliography Resources

• How to Write an Annotated Bibliography
• << Previous: Evaluate Your Info
• Next: Evaluate, Write & Cite >>

Creative Commons Attribution 3.0 License except where otherwise noted.

Land Acknowledgement

The land on which we gather is the unceded territory of the Awaswas-speaking Uypi Tribe. The Amah Mutsun Tribal Band, comprised of the descendants of indigenous people taken to missions Santa Cruz and San Juan Bautista during Spanish colonization of the Central Coast, is today working hard to restore traditional stewardship practices on these lands and heal from historical trauma.

The land acknowledgement used at UC Santa Cruz was developed in partnership with the Amah Mutsun Tribal Band Chairman and the Amah Mutsun Relearning Program at the UCSC Arboretum .

Appropriate Level of Citation

The number of sources you cite in your paper depends on the purpose of your work. For most papers, cite one or two of the most representative sources for each key point. Literature review papers, however, typically include a more exhaustive list of references.

Provide appropriate credit to the source (e.g., by using an in-text citation) whenever you do the following:

• paraphrase (i.e., state in your own words) the ideas of others
• directly quote the words of others
• refer to data or data sets
• reprint or adapt a table or figure, even images from the internet that are free or licensed in the Creative Commons
• reprint a long text passage or commercially copyrighted test item

Avoid both undercitation and overcitation. Undercitation can lead to plagiarism and/or self-plagiarism . Overcitation can be distracting and is unnecessary.

For example, it is considered overcitation to repeat the same citation in every sentence when the source and topic have not changed. Instead, when paraphrasing a key point in more than one sentence within a paragraph, cite the source in the first sentence in which it is relevant and do not repeat the citation in subsequent sentences as long as the source remains clear and unchanged.

Figure 8.1 in Chapter 8 of the Publication Manual provides an example of an appropriate level of citation.

Determining the appropriate level of citation is covered in the seventh edition APA Style manuals in the Publication Manual Section 8.1 and the Concise Guide Section 8.1

Related handouts

• In-Text Citation Checklist (PDF, 227KB)
• Six Steps to Proper Citation (PDF, 112KB)

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How to cite a work with a nonrecoverable source

In most cases, nonrecoverable sources such as personal emails, nonarchived social media livestreams (or deleted and unarchived social media posts), classroom lectures, unrecorded webinars or presentations, and intranet sources should be cited only in the text as personal communications.

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The “outdated sources” myth is that sources must have been published recently, such as the last 5 to 10 years. There is no timeliness requirement in APA Style.

From COVID-19 to demands for social justice: Citing contemporary sources for current events

The guidance in the seventh edition of the Publication Manual makes the process of citing contemporary sources found online easier than ever before.

Citing classical and religious works

A classical or religious work is cited as either a book or a webpage, depending on what version of the source you are using. This post includes details and examples.

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Attend the webinar, “Citing Works in Text Using Seventh Edition APA Style,” on July 14, 2020, to learn the keys to accurately and consistently citing sources in APA Style.

• MJC Library & Learning Center
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Format Papers & Cite Sources

• APA Style, 7th Edition
• Citing Sources
• Avoid Plagiarism
• MLA Style (8th/9th ed.)

APA Tutorial

Formatting your paper, headings organize your paper (2.27), video tutorials, reference list format (9.43).

• Elements of a Reference

Reference Examples (Chapter 10)

Dois and urls (9.34-9.36), in-text citations.

• In-Text Citations Format
• In-Text Citations for Specific Source Types

NoodleTools

• Chicago Style
• Harvard Style
• Other Styles
• Annotated Bibliographies
• How to Create an Attribution

What is APA Style?

APA style was created by social and behavioral scientists to standardize scientific writing. APA style is most often used in:

• psychology,
• social sciences (sociology, business), and

If you're taking courses in any of these areas, be prepared to use APA style.

For in-depth guidance on using this citation style, refer to Publication Manual of the American Psychological Association , 7th ed. We have several copies available at the MJC Library at the call number  BF 76.7 .P83 2020 .

APA Style, 7th ed.

In October 2019, the American Psychological Association made radical changes its style, especially with regard to the format and citation rules for students writing academic papers. Use this guide to learn how to format and cite your papers using APA Style, 7th edition.

You can start by viewing the  video tutorial .

For help on all aspects of formatting your paper in APA Style, see   The Essentials  page on the APA Style website.

• sans serif fonts such as 11-point Calibri, 11-point Arial, or 10-point Lucida Sans Unicode, or
• serif fonts such as 12-point Times New Roman, 11-point Georgia, or normal (10-point) Computer Modern (the default font for LaTeX)
• There are exceptions for the  title page ,  tables ,  figures ,  footnotes , and  displayed equations .
• Margins :  Use 1-in. margins on every side of the page.
• Align the text of an APA Style  paper to the left margin . Leave the right margin uneven, or “ragged.”
• Do not use full justification for student papers.
• Do not insert hyphens (manual breaks) in words at the end of line. However, it is acceptable if your word-processing program automatically inserts breaks in long hyperlinks (such as in a DOI or URL in a reference list entry).
• Indent the first line of each paragraph of text 0.5 in . from the left margin. Use the tab key or the automatic paragraph-formatting function of your word-processing program to achieve the indentation (the default setting is likely already 0.5 in.). Do not use the space bar to create indentation. 
• There are exceptions for the  title page ,  section labels ,  abstract ,  block quotations ,  headings ,  tables and figures ,  reference list , and  appendices .

Paper Elements

Student papers generally include, at a minimum: 

• Title Page (2.3)
• Text (2.11)
• References  (2.12)

Student papers may include additional elements such as tables and figures depending on the assignment. So, please check with your teacher!

Student papers generally  DO NOT  include the following unless your teacher specifically requests it:

• Running head
• Author note

For complete information on the  order of pages , see the APA Style website.

Number your pages consecutively starting with page 1. Each section begins on a new page. Put the pages in the following order:

• Page 1: Title page
• Page 2: Abstract (if your teacher requires an abstract)
• Page 3: Text 
• References begin on a new page after the last page of text
• Footnotes begin on a new page after the references (if your teacher requires footnotes)
• Tables begin each on a new page after the footnotes (if your teacher requires tables) 
• Figures begin on a new page after the tables (if your teacher requires figures)
• Appendices begin on a new page after the tables and/or figures (if your teacher requires appendices)

Sample Papers With Built-In Instructions

To see what your paper should look like, check out these sample papers with built-in instructions.

APA Style uses five (5) levels of headings to help you organize your paper and allow your audience to identify its key points easily. Levels of headings establish the hierarchy of your sections just like you did in your paper outline.

APA tells us to use "only the number of headings necessary to differentiate distinct section in your paper." Therefore, the number of heading levels you create depends on the length and complexity of your paper.

See the chart below for instructions on formatting your headings:

Use Word to Format Your Paper:

Use Google Docs to Format Your Paper:

Placement:  The reference list  appears at the end of the paper, on its own page(s). If your research paper ends on page 8, your References begin on page 9.

Heading:  Place the section label References  in bold at the top of the page, centered.

Arrangement:  Alphabetize entries by author's last name. If source has no named author, alphabetize by the title, ignoring A, An, or The. (9.44-9.48)

Spacing:  Like the rest of the APA paper, the reference list is double-spaced throughout. Be sure NOT to add extra spaces between citations.

Indentation:  To make citations easier to scan, add a  hanging indent  of 0.5 in. to any citation that runs more than one line. Use the paragraph-formatting function of your word processing program to create your hanging indent.  

See Sample References Page (from APA Sample Student Paper):

Elements of Reference List Entries: (Chapter 9)

References generally have four elements, each of which has a corresponding question for you to answer:

• Author:   Who is responsible for this work? (9.7-9.12)
• Date:   When was this work published? (9.13-9.17)
• Title:   What is this work called? (9.18-9.22)
• Source:   Where can I retrieve this work? (9.23-9.37)

By using these four elements and answering these four questions, you should be able to create a citation for any type of source.

For complete information on all of these elements, checkout the APA Style website.

This infographic shows the first page of a journal article. The locations of the reference elements are highlighted with different colors and callouts, and the same colors are used in the reference list entry to show how the entry corresponds to the source.

To create your references, you'll simple look for these elements in your source and put them together in your reference list entry.

American Psychological Association.  Example of where to find reference information for a journal article  [Infographic]. APA Style Center. https://apastyle.apa.org/style-grammar-guidelines/references/basic-principles

Below you'll find two printable handouts showing APA citation examples. The first is an abbreviated list created by MJC Librarians. The second, which is more comprehensive, is from the APA Style website. Feel free to print these for your convenience or use the links to reference examples below:

• APA Citation Examples Created by MJC Librarians for you.
• Common References Examples (APA Handout) Printable handout from the American Psychological Association.
• Journal Article
• Magazine Article
• Newspaper Article
• Edited Book Chapter
• Webpage on a Website

Classroom or Intranet Sources

• Classroom Course Pack Materials
• How to Cite ChatGPT
• Dictionary Entry
• Government Report
• Legal References (Laws & Cases)
• TED Talk References
• Religious Works
• Open Educational Resources (OER)
• Archival Documents and Collections

You can view the entire Reference Examples website below and view a helpful guide to finding useful APA style topics easily:

• APA Style: Reference Examples
• Navigating the not-so-hidden treasures of the APA Style website
• Missing Reference Information

Sometimes you won't be able to find all the elements required for your reference. In that case, see the  instructions in Table 9.1 of the APA style manual in section 9.4 or the APA Style website below:

• Direct Quotation of Material Without Page Numbers

The DOI or URL is the final component of a reference list entry. Because so much scholarship is available and/or retrieved online, most reference list entries end with either a DOI or a URL.

• A  DOI  is a unique alphanumeric string that identifies content and provides a persistent link to its location on the internet. DOIs can be found in database records and the reference lists of published works.
• A  URL  specifies the location of digital information on the internet and can be found in the address bar of your internet browser. URLs in references should link directly to the cited work when possible.

When to Include DOIs and URLs:

• Include a DOI for all works that have a DOI, regardless of whether you used the online version or the print version.
• If an online work has both a DOI and a URL, include only the DOI.
• For works without DOIs from websites (not including academic research databases), provide a URL in the reference (as long as the URL will work for readers).
• For works without DOIs from most academic research databases, do not include a URL or database information in the reference because these works are widely available. The reference should be the same as the reference for a print version of the work.
• For works from databases that publish original, proprietary material available only in that database (such as the UpToDate database) or for works of limited circulation in databases (such as monographs in the ERIC database), include the name of the database or archive and the URL of the work. If the URL requires a login or is session-specific (meaning it will not resolve for readers), provide the URL of the database or archive home page or login page instead of the URL for the work. (See APA Section 9.30 for more information). 
• If the URL is no longer working or no longer provides readers access to the content you intend to cite, try to find an archived version using the Internet Archive , then use the archived URL. If there is no archived URL, do not use that resource.

Format of DOIs and URLs:

Your DOI should look like this: 

https://doi.org/10.1037/a0040251

Follow these guidelines from the APA Style website.

APA Style uses the  author–date citation system , in which a brief in-text citation points your reader to the full reference list entry at the end of your paper. The in-text citation appears within the body of the paper and briefly identifies the cited work by its author and date of publication. This method enables your reader to locate the corresponding entry in the alphabetical reference list at the end of your paper.

Each work you cite  must  appear in the reference list, and each work in the reference list must be cited in the text (or in a table, figure, footnote, or appendix) except for the following (See APA, 8.4):

• Personal communications (8.9)
• General mentions of entire websites, whole periodicals (8.22), and common software and apps (10.10) in the text do not require a citation or reference list entry.
• The source of an epigraph does not usually appear in the reference list (8.35)
• Quotations from your research participants do not need citations or reference list entries (8.36)
• References included in a statistical meta-analysis, which are marked with an asterisk in the reference list, may be cited in the text (or not) at the author’s discretion. This exception is relevant only to authors who are conducting a meta-analysis (9.52).

Formatting Your In-Text Citations

Parenthetical and Narrative Citations: ( See APA Section  8.11)

In APA style you use the author-date citation system for citing references within your paper. You incorporate these references using either a  parenthetical   or a  narrative  style.

Parenthetical Citations

• In parenthetical citations, the author name and publication date appear in parentheses, separated by a comma. (Jones, 2018)
• A parenthetical citation can appear within or at the end of a sentence.
• When the parenthetical citation is at the end of the sentence, put the period or other end punctuation after the closing parenthesis.
• If there is no author, use the first few words of the reference list entry, usually the "Title" of the source: ("Autism," 2008) See APA 8.14
• When quoting, always provide the author, year, and specific page citation or paragraph number for nonpaginated materials in the text (Santa Barbara, 2010, p. 243).  See APA 8.13
• For most citations, the parenthetical reference is placed BEFORE the punctuation: Magnesium can be effective in treating PMS (Haggerty, 2012).

Narrative Citations 

In narrative citations, the author name or title of your source appears within your text and the publication date appears in parentheses immediately after the author name. 

• Santa Barbara (2010) noted a decline in the approval of disciplinary spanking of 26 percentage points from 1968 to 1994.

In-Text Citation Checklist

• In-Text Citation Checklist Use this useful checklist from the American Psychological Association to ensure that you've created your in-text citations correctly.

In-Text Citations for Specific Types of Sources

Quotations from Research Participants

Personal Communications

Secondary Sources  

Use NoodleTools to Cite Your Sources  

NoodleTools can help you create your references and your in-text citations.

• NoodleTools Express No sign in required . When you need one or two quick citations in MLA, APA, or Chicago style, simply generate them in NoodleTools Express then copy and paste what you need into your document. Note: Citations are not saved and cannot be exported to a word processor using NoodleTools Express.
• NoodleTools (Login Full Database) This link opens in a new window Create and organize your research notes, share and collaborate on research projects, compose and error check citations, and complete your list of works cited in MLA, APA, or Chicago style using the full version of NoodleTools. You'll need to Create a Personal ID and password the first time you use NoodleTools.

See How to Use NoodleTools Express to Create a Citation in APA Format

Additional NoodleTools Help

• NoodleTools Help Desk Look up questions and answers on the NoodleTools Web site
• << Previous: MLA Style (8th/9th ed.)
• Next: Chicago Style >>
• Last Updated: Sep 10, 2024 12:08 PM
• URL: https://libguides.mjc.edu/citeyoursources

Except where otherwise noted, this work is licensed under CC BY-SA 4.0 and CC BY-NC 4.0 Licenses .

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How to Cite a Research Paper

Last Updated: March 29, 2024 Fact Checked

This article was reviewed by Gerald Posner and by wikiHow staff writer, Jennifer Mueller, JD . Gerald Posner is an Author & Journalist based in Miami, Florida. With over 35 years of experience, he specializes in investigative journalism, nonfiction books, and editorials. He holds a law degree from UC College of the Law, San Francisco, and a BA in Political Science from the University of California-Berkeley. He’s the author of thirteen books, including several New York Times bestsellers, the winner of the Florida Book Award for General Nonfiction, and has been a finalist for the Pulitzer Prize in History. He was also shortlisted for the Best Business Book of 2020 by the Society for Advancing Business Editing and Writing. There are 8 references cited in this article, which can be found at the bottom of the page. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 420,698 times.

When writing a paper for a research project, you may need to cite a research paper you used as a reference. The basic information included in your citation will be the same across all styles. However, the format in which that information is presented is somewhat different depending on whether you're using American Psychological Association (APA), Modern Language Association (MLA), Chicago, or American Medical Association (AMA) style.

Referencing a Research Paper

• In APA style, cite the paper: Last Name, First Initial. (Year). Title. Publisher.
• In Chicago style, cite the paper: Last Name, First Name. “Title.” Publisher, Year.
• In MLA style, cite the paper: Last Name, First Name. “Title.” Publisher. Year.

Citation Help

• For example: "Kringle, K., & Frost, J."

• For example: "Kringle, K., & Frost, J. (2012)."
• If the date, or any other information, are not available, use the guide at https://blog.apastyle.org/apastyle/2012/05/missing-pieces.html .

• For example: "Kringle, K., & Frost, J. (2012). Red noses, warm hearts: The glowing phenomenon among North Pole reindeer."
• If you found the research paper in a database maintained by a university, corporation, or other organization, include any index number assigned to the paper in parentheses after the title. For example: "Kringle, K., & Frost, J. (2012). Red noses, warm hearts: The glowing phenomenon among North Pole reindeer. (Report No. 1234)."

• For example: "Kringle, K., & Frost, J. (2012). Red noses, warm hearts: The glowing phenomenon among North Pole reindeer. (Report No. 1234). Retrieved from Alaska University Library Archives, December 24, 2017."

• For example: "(Kringle & Frost, 2012)."
• If there was no date on the research paper, use the abbreviation n.d. : "(Kringle & Frost, n.d.)."

• For example: "Kringle, Kris, and Jack Frost."

• For example: "Kringle, Kris, and Jack Frost. "Red Noses, Warm Hearts: The Glowing Phenomenon among North Pole Reindeer." Master's thesis."

• For example: "Kringle, Kris, and Jack Frost. "Red Noses, Warm Hearts: The Glowing Phenomenon among North Pole Reindeer." Master's thesis, Alaska University, 2012."

• For example: "Kringle, Kris, and Jack Frost. "Red Noses, Warm Hearts: The Glowing Phenomenon among North Pole Reindeer." Master's thesis, Alaska University, 2012. Accessed at https://www.northpolemedical.com/raising_rudolf."

• Footnotes are essentially the same as the full citation, although the first and last names of the authors aren't inverted.
• For parenthetical citations, Chicago uses the Author-Date format. For example: "(Kringle and Frost 2012)."

• For example: "Kringle, Kris, and Frost, Jack."

• For example: "Kringle, Kris, and Frost, Jack. "Red Noses, Warm Hearts: The Glowing Phenomenon Among North Pole Reindeer.""

• For example, suppose you found the paper in a collection of paper housed in university archives. Your citation might be: "Kringle, Kris, and Frost, Jack. "Red Noses, Warm Hearts: The Glowing Phenomenon Among North Pole Reindeer." Master's Theses 2000-2010. University of Alaska Library Archives. Accessed December 24, 2017."

• For example: "(Kringle & Frost, p. 33)."

• For example: "Kringle K, Frost J."

• For example: "Kringle K, Frost J. Red noses, warm hearts: The glowing phenomenon among North Pole reindeer."

• For example: "Kringle K, Frost J. Red noses, warm hearts: The glowing phenomenon among North Pole reindeer. Nat Med. 2012; 18(9): 1429-1433."

• For example, if you're citing a paper presented at a conference, you'd write: "Kringle K, Frost J. Red noses, warm hearts: The glowing phenomenon among North Pole reindeer. Oral presentation at Arctic Health Association Annual Summit; December, 2017; Nome, Alaska."
• To cite a paper you read online, you'd write: "Kringle K, Frost J. Red noses, warm hearts: The glowing phenomenon among North Pole reindeer. https://www.northpolemedical.com/raising_rudolf"

• For example: "According to Kringle and Frost, these red noses indicate a subspecies of reindeer native to Alaska and Canada that have migrated to the North Pole and mingled with North Pole reindeer. 1 "

Community Q&A

• If you used a manual as a source in your research paper, you'll need to learn how to cite the manual also. Thanks Helpful 0 Not Helpful 0
• If you use any figures in your research paper, you'll also need to know the proper way to cite them in MLA, APA, AMA, or Chicago. Thanks Helpful 0 Not Helpful 0

You Might Also Like

• ↑ https://askus.library.wwu.edu/faq/116659
• ↑ https://guides.libraries.psu.edu/apaquickguide/intext
• ↑ https://owl.purdue.edu/owl/research_and_citation/chicago_manual_17th_edition/cmos_formatting_and_style_guide/general_format.html
• ↑ https://libanswers.snhu.edu/faq/48009
• ↑ https://www.chicagomanualofstyle.org/tools_citationguide/citation-guide-2.html
• ↑ https://owl.purdue.edu/owl/research_and_citation/mla_style/mla_formatting_and_style_guide/mla_in_text_citations_the_basics.html
• ↑ https://morningside.libguides.com/MLA8/location
• ↑ https://owl.purdue.edu/owl/research_and_citation/ama_style/index.html

About This Article

To cite a paper APA style, start with the author's last name and first initial, and the year of publication. Then, list the title of the paper, where you found it, and the date that you accessed it. In a paper, use a parenthetical reference with the last name of the author and the publication year. For an MLA citation, list the author's last name and then first name and the title of the paper in quotations. Include where you accessed the paper and the date you retrieved it. In your paper, use a parenthetical reference with the author's last name and the page number. Keep reading for tips on Chicago and AMA citations and exceptions to the citation rules! Did this summary help you? Yes No

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Research and Citation Resources

Welcome to the Purdue OWL

This page is brought to you by the OWL at Purdue University. When printing this page, you must include the entire legal notice.

Copyright ©1995-2018 by The Writing Lab & The OWL at Purdue and Purdue University. All rights reserved. This material may not be published, reproduced, broadcast, rewritten, or redistributed without permission. Use of this site constitutes acceptance of our terms and conditions of fair use.

If you are having trouble locating a specific resource please visit the  search page  or the  Site Map . The Citation Chart  provides a detailed overview of MLA Style, APA Style, and Chicago Manual of Style source documentation by category.

Conducting Research

These OWL resources will help you conduct research using primary source methods, such as interviews and observations, and secondary source methods, such as books, journals, and the Internet. This area also includes materials on evaluating research sources.

Using Research

These OWL resources will help you use the research you have conducted in your documents. This area includes material on quoting and paraphrasing your research sources, as well as material on how to avoid plagiarism.

APA Style (7th Edition)

These OWL resources will help you learn how to use the American Psychological Association (APA) citation and format style. This section contains resources on in-text citation and the References page, as well as APA sample papers, slide presentations, and the APA classroom poster.

These OWL resources will help you learn how to use the Modern Language Association (MLA) citation and format style. This section contains resources on in-text citation and the Works Cited page, as well as MLA sample papers, slide presentations, and the MLA classroom poster

Chicago Manual of Style

This section contains information on the Chicago Manual of Style method of document formatting and citation. These resources follow the 17th edition of the Chicago Manual of Style, which was issued in 2017.

Institute of Electrical and Electronics Engineers (IEEE) Style

These resources describe how to structure papers, cite sources, format references, and handle the complexities of tables and figures according to the latest Institute of Electrical and Electronics Engineers (IEEE) guidelines.

American Medical Association (AMA) Style

These resources provide guidance on how to cite sources using American Medical Association (AMA) Style, 10th Ed., including examples for print and electronic sources.

Research Overview

We live in an age overflowing with sources of information. With so many information sources at our fingertips, knowing where to start, sorting through it all and finding what we want can be overwhelming! This handout provides answers to the following research-related questions: Where do I begin? Where should I look for information? What types of sources are available?

Conducting Primary Research

Primary research involves collecting data about a given subject directly from the real world. This section includes information on what primary research is, how to get started, ethics involved with primary research and different types of research you can do. It includes details about interviews, surveys, observations, and analysis.

Evaluating Sources of Information

Evaluating sources of information is an important step in any research activity. This section provides information on evaluating bibliographic citations, aspects of evaluation, reading evaluation, print vs. online sources, and evaluating Internet sources.

Searching Online

This section covers finding information online. It includes information about search engines, Boolean operators, Web directories, and the invisible Web. It also includes an extensive, annotated links section.

Internet References

This page contains links and short descriptions of writing resources including dictionaries, style manuals, grammar handbooks, and editing resources. It also contains a list of online reference sites, indexes for writers, online libraries, books and e-texts, as well as links to newspapers, news services, journals, and online magazines.

Archival Research

This resource discusses conducting research in a variety of archives. It also discusses a number of considerations and best practices for conducting archival research.

This resources was developed in consultation with Purdue University Virginia Kelly Karnes Archives and Special Collections staff.

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Organizing Your Social Sciences Research Paper

• 11. Citing Sources
• Purpose of Guide
• Design Flaws to Avoid
• Independent and Dependent Variables
• Glossary of Research Terms
• Reading Research Effectively
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• Common Grammar Mistakes
• Writing Concisely
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• Footnotes or Endnotes?
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A citation is a formal reference to a published or unpublished source that you consulted and obtained information from while writing your research paper. It refers to a source of information that supports a factual statement, proposition, argument, or assertion or any quoted text obtained from a book, article, web site, or any other type of material . In-text citations are embedded within the body of your paper and use a shorthand notation style that refers to a complete description of the item at the end of the paper. Materials cited at the end of a paper may be listed under the heading References, Sources, Works Cited, or Bibliography. Rules on how to properly cite a source depends on the writing style manual your professor wants you to use for the class [e.g., APA, MLA, Chicago, Turabian, etc.]. Note that some disciplines have their own citation rules [e.g., law; medicine].

Citations: Overview. OASIS Writing Center, Walden University; Research and Citation. The Writing Lab and The OWL. Purdue University; Citing Sources. University Writing Center, Texas A&M University.

Citing Your Sources

Reasons for Citing Sources in Your Research Paper

English scientist, Sir Isaac Newton, once wrote, "If I have seen further, it is by standing on the shoulders of giants.”* Citations support learning how to "see further" through processes of intellectual discovery, critical thinking, and applying a deliberate method of navigating through the scholarly landscape by tracking how cited works are propagated by scholars over time and the subsequent ways this leads to the devarication of new knowledge.

Listed below are specific reasons why citing sources is an important part of doing good research.

• Shows the reader where to find more information . Citations help readers expand their understanding and knowledge about the issues being investigated. One of the most effective strategies for locating authoritative, relevant sources about a research problem is to review materials cited in studies published by other authors. In this way, the sources you cite help the reader identify where to go to examine the topic in more depth and detail.
• Increases your credibility as an author . Citations to the words, ideas, and arguments of scholars demonstrates that you have conducted a thorough review of the literature and, therefore, you are reporting your research results or proposing recommended courses of action from an informed and critically engaged perspective. Your citations offer evidence that you effectively contemplated, evaluated, and synthesized sources of information in relation to your conceptualization of the research problem.
• Illustrates the non-linear and contested nature of knowledge creation . The sources you cite show the reader how you characterized the dynamics of prior knowledge creation relevant to the research problem and how you managed to identify the contested relationships between problems and solutions proposed among scholars. Citations don't just list materials used in your study, they tell a story about how prior knowledge-making emerged from a constant state of creation, renewal, and transformation.
• Reinforces your arguments . Sources cited in your paper provide the evidence that readers need to determine that you properly addressed the “So What?” question. This refers to whether you considered the relevance and significance of the research problem, its implications applied to creating new knowledge, and its importance for improving practice. In this way, citations draw attention to and support the legitimacy and originality of your own ideas and assertions.
• Demonstrates that you "listened" to relevant conversations among scholars before joining in . Your citations tell the reader where you developed an understanding of the debates among scholars. They show how you educated yourself about ongoing conversations taking place within relevant communities of researchers before inserting your own ideas and arguments. In peer-reviewed scholarship, most of these conversations emerge within books, research reports, journal articles, and other cited works.
• Delineates alternative approaches to explaining the research problem . If you disagree with prior research assumptions or you believe that a topic has been understudied or you find that there is a gap in how scholars have understood a problem, your citations serve as the source materials from which to analyze and present an alternative viewpoint or to assert that a different course of action should be pursued. In short, the materials you cite serve as the means by which to argue persuasively against long-standing assumptions promulgated in prior studies.
• Helps the reader understand contextual aspects of your research . Cited sources help readers understand the specific circumstances, conditions, and settings of the problem being investigated and, by extension, how your arguments can be fully understood and assessed. Citations place your line of reasoning within a specific contextualized framework based on how others have studied the problem and how you interpreted their findings in support of your overall research objectives.
• Frames the development of concepts and ideas within the literature . No topic in the social and behavioral sciences rests in isolation from research that has taken place in the past. Your citations help the reader understand the growth and transformation of the theoretical assumptions, key concepts, and systematic inquiries that emerged prior to your engagement with the research problem.
• Underscores sources that were most important to you . Your citations represent a set of choices made about what you determined to be the most important sources for understanding the topic. They not only list what you discovered, but why it matters and how the materials you chose to cite fit within the broader context of your research design and arguments. As part of an overall assessment of the study’s validity and reliability , the choices you make also helps the reader determine what sources of research may have been excluded.
• Provides evidence of interdisciplinary thinking . An important principle of good research is to extend your review of the literature beyond the predominant disciplinary space where scholars have previously examined a topic. Citations provide evidence that you have integrated epistemological arguments, observations, and/or methodological strategies of other disciplines into your paper, thereby demonstrating that you understand the complex, interconnected nature of contemporary research topics.
• Forms the basis for bibliometric analysis of research . Bibliometric analysis is a quantitative method used, for example, to identify and predict emerging trends in research, document patterns of collaboration among scholars, explore the intellectual structure of a specific domain of research, map the development of research within and across disciplines, or identify gaps in knowledge within the literature. Bibliometric data can also be used to visually map relationships among published studies. Citations to books, journal articles, research reports, and other publications represent the raw data used in bibliometric research.
• Reveals possible adherence to the principles of citational justice. Citational justice refers to equity in the inclusion of sources published by authors who are members of marginalized or underrepresented groups that are often under-cited because of their background, community of origin, identity, or location. In so doing, this movement “challenges entrenched hierarchies and biases in knowledge production.” ** Within this context, the sources cited in your paper can help the reader obtain a more inclusive divergency of voices and perspectives about how a research problem can be understood, contextualized, and investigated.
• Supports critical thinking and independent learning . Evaluating the authenticity, reliability, validity, and originality of prior research is an act of interpretation and introspective reasoning applied to assessing whether a source of information will contribute to understanding the problem in ways that are persuasive and align with your overall research objectives. Reviewing and citing prior studies represents a deliberate act of critically scrutinizing each source as part of your overall assessment of how scholars have confronted the research problem.
• Honors the achievements of others . As Susan Blum recently noted, *** citations not only identify sources used, they acknowledge the achievements of scholars within the larger network of research about the topic. Citing sources is a normative act of professionalism within academe and a way to highlight and recognize the work of scholars who likely do not obtain any tangible benefits or monetary value from their research endeavors. Your citations help to validate the work of others.

*Vernon. Jamie L. "On the Shoulder of Giants." American Scientist 105 (July-August 2017): 194.

**Dadze Arthur, Abena and Mary S. Mangai. "The Journal and the Quest for Epistemic Justice." Public Administration and Development 44 (2024): 11.

***Blum, Susan D. "In Defense of the Morality of Citation.” Inside Higher Ed , January 29, 2024.

Aksnes, Dag W., Liv Langfeldt, and Paul Wouters. "Citations, Citation Indicators, and Research Quality: An Overview of Basic Concepts and Theories." Sage Open 9 (January-March 2019): https://doi.org/10.1177/2158244019829575; Blum, Susan Debra. My Word!: Plagiarism and College Culture . Ithaca, NY: Cornell University Press, 2009; Bretag, Tracey., editor. Handbook of Academic Integrity . Singapore: Springer Singapore, 2020; Ballenger, Bruce P. The Curious Researcher: A Guide to Writing Research Papers . 7th edition. Boston, MA: Pearson, 2012; D'Angelo, Barbara J. "Using Source Analysis to Promote Critical Thinking." Research Strategies 18 (Winter 2001): 303-309; Kwon, Diana. “The Rise of Citational Justice.” Nature 603 (March 24, 2022): 568-572; Donthu, Naveen et al. “How to Conduct a Bibliometric Analysis: An Overview and Guidelines.” Journal of Business Research 133 (2021): 285-296; Mauer, Barry and John Venecek. “Scholarship as Conversation.” Strategies for Conducting Literary Research, University of Central Florida, 2021; Öztürk, Oguzhan, Ridvan Kocaman, and Dominik K. Kanbach. "How to Design Bibliometric Research: An Overview and a Framework Proposal." Review of Managerial Science (2024): 1-29; Why Cite? Poorvu Center for Teaching and Learning, Yale University; Citing Information. The Writing Center. University of North Carolina; Harvard Guide to Using Sources. Harvard College Writing Program. Harvard University; Newton, Philip. "Academic Integrity: A Quantitative Study of Confidence and Understanding in Students at the Start of Their Higher Education."  Assessment and Evaluation in Higher Education 41 (2016): 482-497; Referencing More Effectively. Academic Skills Centre. University of Canberra; Using Sources. Yale College Writing Center. Yale University; Vosburgh, Richard M. "Closing the Academic-practitioner Gap: Research Must Answer the “SO WHAT” Question." H uman Resource Management Review 32 (March 2022): 100633; When and Why to Cite Sources. Information Literacy Playlists, SUNY, Albany Libraries.

Structure and Writing Style

Referencing your sources means systematically showing what information or ideas you acquired from another author’s work, and identifying where that information come from . You must cite research in order to do research, but at the same time, you need to delineate what are your original thoughts and ideas and what are the thoughts and ideas of others. Citations establish the demarcation between each set of statements. Procedures used to cite sources vary among different fields of study. If not outlined in your course syllabus or writing assignment, always speak with your professor about what writing style for citing sources should be used for the class because it is important to fully understand the citation rules that should be used in your paper and to apply them consistently. If your professor defers and tells you to "choose whatever you want, just be consistent," then choose the citation style you are most familiar with or that is appropriate to your major [e.g., use Chicago style if you are majoring in history; use APA if its an education course; use MLA if it is a general writing course].

For examples of common citation styles, GO HERE .

GENERAL GUIDELINES

1. Are there any reasons I should avoid referencing other people's work? No. If placed in the proper context, r eferencing other people's research is never an indication that your work is substandard or lacks originality. In fact, the opposite is true. If you write your paper without adequate references to previous studies, you are signaling to the reader that you are not familiar with the literature on the topic, thereby, undermining the validity of your study and your credibility as a researcher. Including references in academic writing is one of the most important ways to demonstrate your knowledge and understanding of how the research problem has been addressed. It is the intellectual packaging around which you present your thoughts, ideas, and arguments to the reader.

2. What should I do if I find out that my great idea has already been studied by another researcher? It can be frustrating to come up with what you believe is a great topic for your paper only to discover that it's already been thoroughly studied. However, do not become frustrated by this. You can acknowledge the prior research by writing in the text of your paper [see also Smith, 2002], then citing the complete source in your list of references. Use the discovery of prior studies as an opportunity to demonstrate the significance of the problem being investigated and, if applicable, as a means of delineating your analysis from those of others [e.g., the prior study is ten years old and doesn't take into account new variables]. Strategies for responding to prior research can include: stating how your study updates previous understandings about the topic, offering a new or different perspective, applying a different or innovative method of gathering and interpreting data, and/or describing a new set of insights, guidelines, recommendations, best practices, or working solutions.

3. What should I do if I want to use an adapted version of someone else's work? You still must cite the original work. For example, you use a table of statistics from a journal article published in 1996 by author Smith, but you have altered or added new data to it. Reference the revised chart, such as, [adapted from Smith, 1996], then cite the original source in your list of references. You can also use other terms in order to specify the exact relationship between the original source and the version you have presented, such as, "based on data from Smith [1996]...," or "summarized from Smith [1996]...." Citing the original source helps the reader locate where the information was first presented and under what context it was used as well as to evaluate how effectively you adapted it to your own research.

4. What should I do if several authors have published very similar information or ideas? You can indicate that the topic, idea, concept, or information can be found in the works of others by stating something similar to the following example: "Though many scholars have applied rational choice theory to understanding economic relations among nations [Smith, 1989; Jones, 1991; Johnson, 1994; Anderson, 2003; Smith, 2014], little attention has been given to applying the theory to examining the influence of non-governmental organizations in a globalized economy." If you only reference one author or only the most recent study, then your readers may assume that only one author has published on this topic, or more likely, they will conclude that you have not conducted a thorough review of the literature. Referencing all relevant authors of prior studies gives your readers a clear idea of the breadth of analysis you conducted in preparing to study the research problem. If there has been a significant number of prior studies on the topic [i.e., ten or more], describe the most comprehensive and recent works because they will presumably discuss and reference the older studies. However, note in your review of the literature that there has been significant scholarship devoted to the topic so the reader knows that you are aware of the numerous prior studies.

5. What if I find exactly what I want to say in the writing of another researcher? In the social sciences, the rationale in duplicating prior research is generally governed by the passage of time, changing circumstances or conditions, or the emergence of variables that necessitate new investigations . If someone else has recently conducted a thorough investigation of precisely the same research problem that you intend to study, then you likely will have to revise your topic, or at the very least, review this literature to identify something new to say about the problem. However, if it is someone else's particularly succinct expression, but it fits perfectly with what you are trying to say, then you can quote from the author directly, referencing the source. Identifying an author who has made the exact same point that you want to make can be an opportunity to validate, as well as reinforce the significance of, the research problem you are investigating. The key is to build on that idea in new and innovative ways. If you are not sure how to do this, consult with a librarian .

6. Should I cite a source even if it was published long ago? Any source used in writing your paper should be cited, regardless of when it was written. However, in building a case for understanding prior research about your topic, it is generally true that you should focus on citing more recently published studies because they presumably have built upon the research of older studies. When referencing prior studies, use the research problem as your guide when considering what to cite. If a study from forty years ago investigated the same topic, it probably should be examined and considered in your list of references because the research may have been foundational or groundbreaking at the time, even if its findings are no longer relevant to current conditions or reflect current thinking [one way to determine if a study is foundational or groundbreaking is to examine how often it has been cited in recent studies using the "Cited by" feature of Google Scholar ]. However, if an older study only relates to the research problem tangentially or it has not been cited in recent studies, then it may be more appropriate to list it under further readings .

7. Can I cite unusual and non-scholarly sources in my research paper? The majority of the citations in a research paper should be to scholarly [a.k.a., academic; peer-reviewed] studies that rely on an objective and logical analysis of the research problem based on empirical evidence that reliably supports your arguments. However, any type of source can be considered valid if it brings relevant understanding and clarity to the topic. This can include, for example, non-textual elements such as photographs, maps, or illustrations. A source can include materials from special or archival collections, such as, personal papers, manuscripts, business memorandums, the official records of an organization, or digitized collections. Citations can also be to unusual items, such as, an audio recording, a transcript from a television news program, a unique set of data, or a social media post. The challenge is knowing how to cite unusual and non-scholarly sources because they often do not fit within consistent citation rules of books or journal articles. Given this, consult with a librarian if you are unsure how to cite a source.

NOTE:   In any academic writing, you are required to identify which ideas, facts, thoughts, concepts, or declarative statements are yours and which are derived from the research of others. The only exception to this rule is information that is considered to be a commonly known fact [e.g., "George Washington was the first president of the United States"] or a statement that is self-evident [e.g., "Australia is a country in the Global South"]. Appreciate, however, that any "commonly known fact" or self-evidencing statement is culturally constructed and shaped by specific social and aesthetical biases . If you have any doubt about whether or not a fact is considered to be widely understood knowledge, provide a supporting citation, or, ask your professor for clarification about whether the statement should be cited.

ANOTHER NOTE:   What is a foundational or groundbreaking study? In general, this refers to a study that investigated a research problem which , up to that point, had never been clearly defined or explained. If you trace a research topic back in time using citations as your guide, you will often discover an original study or set of studies that was the first to identify, explain the significance, and thoroughly investigate a problem. It is considered f oundational or groundbreaking because it pushed the boundaries of existing knowledge and influenced how researchers thought about the problem in new or innovative ways. Evidence of  foundational or groundbreaking research is the number of times a study has been subsequently cited, and continues to be cited, since it was first published.

Ballenger, Bruce P. The Curious Researcher: A Guide to Writing Research Papers . 7th edition. Boston, MA: Pearson, 2012; Blum, Susan Debra. My Word!: Plagiarism and College Culture . Ithaca, NY: Cornell University Press, 2009; Bretag, Tracey., editor. Handbook of Academic Integrity . Singapore: Springer Singapore, 2020; Carlock, Janine. Developing Information Literacy Skills: A Guide to Finding, Evaluating, and Citing Sources . Ann Arbor, MI: University of Michigan Press, 2020; Harvard Guide to Using Sources. Harvard College Writing Program. Harvard University; How to Cite Other Sources in Your Paper. The Structure, Format, Content, and Style of a Journal-Style Scientific Paper. Department of Biology. Bates College; Lunsford, Andrea A. and Robert Connors; The St. Martin's Handbook . New York: St. Martin's Press, 1989; Mills, Elizabeth Shown. Evidence Explained: Citing History Sources from Artifacts to Cyberspace . 3rd edition. Baltimore, MD: Genealogical Publishing Company, 2015; Research and Citation Resources. The Writing Lab and The OWL. Purdue University; Writing Tutorial Services, Center for Innovative Teaching and Learning. Indiana University; Why Cite? Poorvu Center for Teaching and Learning, Yale Univeraity.

Other Citation Research Guides

The following USC Libraries research guide can help you properly cite sources in your research paper:

• Citation Guide

The following USC Libraries research guide offers basic information on using images and media in research:

Listed below are particularly well-done and comprehensive websites that provide specific examples of how to cite sources under different style guidelines.

• Purdue University Online Writing Lab
• Southern Cross University Harvard Referencing Style
• University of Wisconsin Writing Center

This is a useful guide concerning how to properly cite images in your research paper.

• Colgate Visual Resources Library, Citing Images

This guide provides good information on the act of citation analysis, whereby you count the number of times a published work is cited by other works in order to measure the impact of a publication or author.

Measuring Your Impact: Impact Factor, Citation Analysis, and other Metrics: Citation Analysis [Sandy De Groote, University of Illinois, Chicago]

Automatic Citation Generators

The links below lead to systems where you can type in your information and have a citation compiled for you. Note that these systems are not foolproof so it is important that you verify that the citation is correct and check your spelling, capitalization, etc. However, they can be useful in creating basic types of citations, particularly for online sources.

• BibMe -- APA, MLA, Chicago, and Turabian styles
• DocsCite -- for citing government publications in APA or MLA formats
• EasyBib -- APA, MLA, and Chicago styles
• Son of Citation Machine -- APA, MLA, Chicago, and Turabian styles

NOTE:   Many companies that create the research databases the USC Libraries subscribe to, such as ProQuest , include built-in citation generators that help take the guesswork out of how to properly cite a work. When available, you should always utilize these features because they not only generate a citation to the source [e.g., a journal article], but include information about where you accessed the source [e.g., the database].

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• Boston University Libraries

WR151: The World of Higher Education

Citing your sources.

• Finding Scholarly Books & Articles
• Finding News
• Finding Data
• Finding Art, Images, Sound & Video
• Search Strategies

Proper citation is an essential aspect of scholarship. Citing properly allows your reader or audience to locate the materials you have used. Most importantly, citations give credit to the authors of quoted or consulted information.

For detailed instructions on how to cite within the text of your paper, please consult a style manual listed below. Although these sources do not cover every possibility you might encounter when trying to cite your sources, a style manual can help you  create your bibliography.

Here are some easy web options .

MLA (Modern Language Association) Style

• Purdue OWL (Online Writing Lab) MLA Style Introduction

APA (American Psychological Association) Style

• Purdue OWL (Online Writing Lab) APA Style Introduction
• APA Reference examples

American Psychological Association

Chicago Style

• Purdue OWL (Online Writing Lab) Chicago Manual of Style

Need help? 

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• Email   Get answers within 24 hours. ( [email protected] )
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APA 7th Edition Citation Examples

• Volume and Issue Numbers
• Page Numbers
• Undated Sources
• Citing a Source Within a Source

Citing a Source within a Source

• In-Text Citations
• Academic Journals
• Encyclopedia Articles
• Book, Film, and Product Reviews
• Online Classroom Materials
• Conference Papers
• Technical + Research Reports
• Court Decisions
• Treaties and Other International Agreements
• Federal Regulations: I. The Code of Federal Regulations
• Federal Regulations: II. The Federal Register
• Executive Orders
• Charter of the United Nations
• Federal Statutes
• Dissertations and Theses
• Interviews, E-mail Messages + Other Personal Communications
• Social Media
• Business Sources
• PowerPoints
• AI: ChatGPT, etc.

Scenario: You read a 2007 article by Linhares and Brum that cites an earlier article, by Klein. You want to cite Klein's article, but you have not read Klein's article itself.

Reference list citation

Linhares, A., & Brum, P. (2007). Understanding our understanding of strategic scenarios: What role do chunks play? Cognitive Science , 31 (6), 989-1007. https://doi.org/10.1080/03640210701703725

Your Reference list will contain the article you read, by Linhares and Brum. Your Reference list will NOT contain a citation for Klein's article.

In-text citation

Klein's study (as cited in Linhares & Brum, 2007) found that...

Your in-text citation gives credit to Klein and shows the source in which you found Klein's ideas.

See  Publication Manual , p. 258.

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Citing Sources: Citation Styles

Citation manuals & resources.

There are varying ways to cite sources. Usually, a short form of the citation is included within the text of the paper (referred to as in-text or parenthetical citations) and then the full citation is given on the last page of the paper, sometimes referred to as a "Works Cited" page, a "References," list or a "Bibliography." Also, there are different styles to citing sources. The following styles are commonly used:

• APA (American Psychological Association) Format is generally used to cite sources within the social sciences.
• MLA (Modern Language Association) Format is generally used to cite sources within the humanities and liberal arts.

Print Citation Guides:

• MLA Handbook Library Reference Z253 .M634 2021
• Publication Manual of the American Psychological Association Library Reference Z253 .P83 2020
• Turabian Style Manual: A Manual for Writers of Term Papers, Theses, and Dissertations Library Reference Z253 .T8 2013
• The Chicago Manual of Style Library Reference Z253 .U69 2017

Citation Guides Online:

• MLA Formatting and Style Guide
• From OWL Purdue University Online Writing Lab
• APA Style and Grammar Guide From the American Psychological Association
• Chicago Manual of Style Online
• Guide to Turabian Style
• "Citing Information: Introduction" Self-paced instructional tutorials for various citation styles, as well as an introduction to citation. (From the Libraries of University of North Carolina at Chapel Hill)

Parts of a Citation

Plagiarism - what it is and how to avoid it.

Whether intentional or accidental, plagiarism is a violation of Salve Regina University's Academic Honor Code, which states that

"all students are expected to accept and abide by the values of honesty, integrity, and truthfulness in their academic pursuits." Penalties for violating the Academic Honor Code can range from failure for the assignment involved to failure of the course.Any violation can result in dismissal from the University."

• Copying, quoting, paraphrasing, or summarizing from any source without giving proper credit.
• Submitting another's work as your own.
• Purchasing or downloading a paper and turning it in as your own work.

      (Source: Taken from "Preventing Plagiarism: A Guide for Students" from the Staley Library at Millikin University)

• Directly quote another person's written or spoken words. Be sure to enclose these words and/or sentences in quotations marks!
• Paraphrase another person's spoken or written words. Paraphrase means to re-write in your own words; merely reordering or substituting words is still considered plagiarism!
• Use theories, ideas, opinions, research, etc. that are not your own.
• Use historical, statistical, or scientific facts or data that are not your own.

        (Source: Taken from "Plagiarism: What It is and How to Recognize and Avoid It" from Writing Tutorial Services at Indiana University)

Why do I need to cite sources?

• anyone reading your paper can easily find your sources
• the words and ideas used from your sources are not assumed to be your own
• authors and researchers are properly credited for their original work

Where can I find more information on plagiarism?

• "Using Research" (From the Online Writing Lab (OWL) at Purdue University)
• "Research 101: Plagiarism" (From Ithaca College Library)
• "Avoiding Plagiarism - A Guide for Students" (From University of Oregon Libraries)

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The American Astronomical Society (AAS) , established in 1899 and based in Washington, DC, is the major organization of professional astronomers in North America. Its membership of about 7,000 individuals also includes physicists, mathematicians, geologists, engineers, and others whose research and educational interests lie within the broad spectrum of subjects comprising contemporary astronomy. The mission of the AAS is to enhance and share humanity's scientific understanding of the universe.

The Institute of Physics (IOP) is a leading scientific society promoting physics and bringing physicists together for the benefit of all. It has a worldwide membership of around 50 000 comprising physicists from all sectors, as well as those with an interest in physics. It works to advance physics research, application and education; and engages with policy makers and the public to develop awareness and understanding of physics. Its publishing company, IOP Publishing, is a world leader in professional scientific communications.

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Resolving a Candidate Dual Active Galactic Nucleus with ∼100 pc Separation in MCG-03-34-64

Anna Trindade Falcão 1 , T. J. Turner 2 , S. B. Kraemer 3 , J. Reeves 3,4 , V. Braito 3,4,5 , H. R. Schmitt 6 , and L. Feuillet 3

Published 2024 September 9 • © 2024. The Author(s). Published by the American Astronomical Society. The Astrophysical Journal , Volume 972 , Number 2 Citation Anna Trindade Falcão et al 2024 ApJ 972 185 DOI 10.3847/1538-4357/ad6b91

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Author affiliations.

1 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA

2 Eureka Scientific, Inc., 2452 Delmer St., Suite 100, Oakland, CA 94602, USA

3 Institute for Astrophysics and Computational Sciences, The Catholic University of America, Washington, DC 20064, USA

4 INAF—Osservatorio Astronomico di Brera, Via Bianchi 46, 23807, Merate (LC), Italy

5 Dipartimento di Fisica, Università di Trento, Via Sommarive 14, Trento 38123, Italy

6 Naval Research Laboratory, Washington, DC 20375, USA

Anna Trindade Falcão https://orcid.org/0000-0001-8112-3464

T. J. Turner https://orcid.org/0000-0003-2971-1722

S. B. Kraemer https://orcid.org/0000-0003-4073-8977

J. Reeves https://orcid.org/0000-0003-3221-6765

V. Braito https://orcid.org/0000-0002-2629-4989

H. R. Schmitt https://orcid.org/0000-0003-2450-3246

L. Feuillet https://orcid.org/0000-0002-5718-2402

• Received 2024 May 24
• Revised 2024 July 20
• Accepted 2024 August 4
• Published 2024 September 9

AGN host galaxies ; Seyfert galaxies ; High energy astrophysics

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We report the serendipitous multiwavelength discovery of a candidate dual black hole system with a separation of ∼100 pc, in the gas-rich luminous infrared galaxy MCG-03-34-64 ( z = 0.016). Hubble Space Telescope/Advanced Camera for Surveys observations show three distinct optical centroids in the [O iii ] narrow-band and F814W images. Subsequent analysis of Chandra/ACIS data shows two spatially resolved peaks of equal intensity in the neutral Fe K α (6.2–6.6 keV) band, while high-resolution radio continuum observations with the Very Large Array at 8.46 GHz (3.6 cm band) show two spatially coincident radio peaks. Fast shocks as the ionizing source seem unlikely, given the energies required for the production of Fe K α . If confirmed, the separation of ∼100 pc would represent the closest dual active galactic nuclei reported to date with spatially resolved, multiwavelength observations.

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1. Introduction

The masses of supermassive black holes (SMBHs) in active galactic nuclei (AGNs) correlate with the global properties of their host galaxies' stellar components, such as luminosity, mass, and velocity dispersion, extending over kiloparsec scales (e.g., Kormendy & Ho 2013 ). This correlation highlights the need to understand the mechanisms driving SMBH growth.

Both galactic evolutionary models and observations suggest that a significant fraction of AGNs, particularly those at the center of large-scale structures, undergo major mergers (e.g., De Lucia & Blaizot 2007 ; Hopkins et al. 2008 ; Ginolfi et al. 2017 ; Castignani et al. 2020 ). Hydrodynamical simulations further demonstrate that major mergers induce gas inflows toward galactic centers, potentially triggering both star formation and accretion onto central SMBHs (Mayer et al. 2007 ). However, the overall impact of these events on SMBH growth throughout cosmic time remains poorly constrained.

SMBH pairs, often manifested as dual AGNs, provide distinctive evidence for merger-fueled SMBH growth (e.g., Wassenhove et al. 2012 ). Numerous dual AGN candidates have been identified using various techniques, including optical spectroscopy with emission line ratios (e.g., Liu et al. 2011 ), hard X-ray emission (e.g., Koss et al. 2011 ), and double-peaked narrow emission lines (e.g., Smith et al. 2010 ; Koss et al. 2023 ). Nonetheless, these methods have limitations, and multiwavelength follow-up observations have revealed a substantial number of false positives (e.g., Fu et al. 2011b ).

The advent of gravitational-wave astronomy, with the potential for detection through pulsar timing arrays (e.g., Verbiest et al. 2016 ), has heightened the importance of understanding the formation timescales of binary systems. Studying kiloparsec and subkiloparsec dual AGNs offers a unique window into the final stages of SMBH binary coalescence, a crucial process in gravitational wave astronomy.

Dual AGNs separated by kiloparsec or subkiloparsec scales are inherently more challenging to detect and investigate than wider-separation systems (e.g., >3 kpc). This difficulty arises from increased obscuration in late-stage mergers (e.g., Koss et al. 2016 ; Ricci et al. 2021 ; De Rosa et al. 2022 ), limitations in telescope spatial resolution (particularly at subkiloparsec scales), the scarcity of detected radio-bright dual systems (Burke-Spolaor 2011 ), and the limitations of optical selection using double-peaked narrow emission lines (prone to false positives; see Fu et al. 2011a ). Existing observations of dual AGNs tentatively suggest that AGN triggering becomes more prevalent in advanced mergers with stellar bulge separations <10 kpc (e.g., Koss et al. 2010 ; Fu et al. 2018 ; Stemo et al. 2021 ), aligning with simulations of SMBH accretion and evolution in such mergers (e.g., Blecha et al. 2018 ). Therefore, studying nearby galaxies hosting dual AGNs separated at subkiloparsec scales is crucial for advancing our understanding of the late stages of galaxy mergers, the triggering and fueling of AGN activity, and the dynamics of SMBH pairs (Steinborn et al. 2016 ). These close-separation systems provide a unique window into the processes leading to the eventual coalescence of SMBHs, which is a major source of gravitational waves, and plays a fundamental role in the growth of SMBHs and their host galaxies (Dotti et al. 2012 ; Kharb et al. 2017 ).

While several dual AGN candidates have been proposed at scales of hundreds of parsecs, often supported by single-wave band observations, these have frequently been challenged by subsequent studies. Notable examples include the nearby Seyfert NGC 3393 (Fabbiano et al. 2011 ), SDSS J101022.95 + 141300.9 (Goulding et al. 2019 ), and a third active nucleus in NGC 6240 (Kollatschny et al. 2020 ), later disputed in other works (Koss et al. 2015 ; Veres et al. 2021 ; Treister et al. 2020 ).

In this study, we present the serendipitous discovery of a candidate dual AGN system in MCG-03-34-64 (IRAS 13197-1627), a nearby early-type infrared luminous galaxy at z = 0.01654 (∼78 Mpc, from NASA/IPAC Extragalactic Database). 7 This galaxy is identified as one of the hardest X-ray sources in the local Universe (Tatum et al. 2016 ). Earlier X-ray observations with ASCA, XMM-Newton, and BeppoSAX (Dadina & Cappi 2004 ; Miniutti et al. 2007 ) revealed an extremely hard and complex source spectrum, attributed to heavy absorption from a multilayered and clumpy medium. MCG-03-34-64 also shows extended radio emission (∼300 pc), roughly aligned with the major axis of the host galaxy (Schmitt et al. 2001 ), and ∼2'' extent in mid-infrared aligned in the same direction as the radio structure (Hönig et al. 2010 ).

We have obtained Hubble Space Telescope/Advanced Camera for Surveys (ACS) imaging of MCG-03-34-64 in 2022 June (P.I.: Turner, proposal ID: 16847), and 50 ks of Chandra/ACIS-S observations in 2023 April (obs ids 25253, 27802, and 27803, P.I.: Turner). This paper presents the results of the analysis of these new data sets, combined with existing Very Large Array (VLA) radio, and Hubble Space Telescope (HST) optical imaging of the source. Throughout this paper, we adopt Ω m = 0.3, Ω Λ = 0.7, and H 0 = 70 km s −1 Mpc −1 , and a scale of 340 pc arcsec −1 , based on the redshift at the galaxy's distance.

2. Multiwavelength Observations and Analysis

Table 1 lists all observations used in this paper, including instruments, filters, observation dates, obs ids, and exposure times. Details on the reduction of new HST/ACS and Chandra/ACIS-S observations are provided in Sections 2.1 and 2.2 , respectively. For reduction and analysis of archival HST F814W, VLA 8.46 GHz imaging, and Suzaku and XMM-Newton spectroscopy, see Section 2.3 . All the HST data used in this paper can be found in MAST at doi: 10.17909/53rj-fw34 .

Table 1.  Multiwavelength Observations of MCG-03-34-64

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2.1. Hubble Space Telescope Imaging

HST/ACS observations of MCG-03-34-64 were obtained using the linear ramp filter FR505N (narrow-band [O iii ]) centered at 5089.6 Å, to characterize the morphology of the emission-line gas, while a continuum medium band image was obtained using FR647M, centered at 5590 Å. These filters have bandwidths of 2% and 9%, respectively. Standard HST pipeline procedures were employed for data reduction. The narrow-band and continuum images were acquired sequentially and did not require realignment. Flux calibration was performed using information available on the headers.

2.2. Chandra Imaging and Spectroscopy.

Subpixel imaging binning was employed to effectively oversample the Chandra point-spread function (PSF) and overcome the limitations of the ACIS instrumental pixel size. This method has been extensively used and validated in previous studies examining the subkiloparsec regions around nearby and obscured AGNs (e.g., Maksym et al. 2017 ; Fabbiano et al. 2018a ; Ma et al. 2021 ; Trindade Falcão 2023 ), demonstrating excellent agreement between reconstructed ACIS-S features and those imaged with higher spatial resolution instruments such as HST and VLA (e.g., Wang et al. 2011b ; Paggi et al. 2012 ; Maksym et al. 2019 ; Fabbiano et al. 2018b ). The Chandra PSF was simulated using ChaRT 9 and MARX . 10 This work uses a final Chandra scale of one-eighth of the native ACIS pixel.

2.3. Archival Radio/Optical/X-Ray Observations

In addition to the new Chandra and HST data sets, we analyze archival optical, radio, and X-ray observations of MCG-03-34-64, as listed in Table 1 . These data include 8.46 GHz radio imaging with VLA, optical continuum imaging with HST/ACS F814W, and X-ray spectra from Suzaku and XMM-Newton.

There are four additional archival Chandra observations with MCG-03-34-64 in the field of view (obs ids 27267, 27786, 7373, and 23690). However, three of these observations are not usable due to the galaxy being located at the very edge of the field (observations were optimized for the companion galaxy). The fourth available Chandra observation consists of a 7 ks snapshot (used in Miniutti et al. 2007 ), which has insufficient counts for meaningful imaging analysis.

3.1. Imaging Analysis

3.1.1. hubble space telescope imaging.

The [O iii ] narrow-line region (NLR) in MCG-03-34-64 has a highly unusual morphology, featuring three distinct, and compact emission regions, as shown in Figure 1 . The NLR extends ∼2.3 kpc along the NE–SW direction. In the perpendicular direction (NW–SE), we observe three diffraction spikes characteristic of point sources, while one diffraction spike is observed along the NE–SW cone. These features suggest high concentrations of [O iii ] gas within a relatively small region, a rare occurrence in the local Universe (Fischer et al. 2018 ).

Figure 1.  HST [O iii ] and F814W images of the central region of MCG-03-34-64. Note the prominent diffraction spikes present in the [O iii ] image.

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To examine the overall structure of the NLR, we model the [O iii ] light distribution with GALFIT (Peng et al. 2002 , 2010 ). The modeling was performed with generic Sérsic profiles, and we allow all parameters to freely vary during the fitting process. The background level and standard deviation were determined from blank regions within the image's field of view.

The best-fit GALFIT model consists of four Sérsic components, one for each of the three peaks visible in the [O iii ] surface plot in the leftmost panel of Figure 2 , and an additional larger component to take into account the underlying fainter, more extended emission. In the second panel, we show a zoomed-in image of the [O iii ] emission, and mark the position of each Sérsic component corresponding to a strong peak of [O iii ] emission as green circles. The third panel of Figure 2 shows the best-fit GALFIT model, while the fourth panel shows the residual images from this best-fit model, with the different model components subtracted from the data.

Figure 2.  First panel: surface plot of the [O iii ] flux in the HST/ACS image where three distinct sources are visible. Second panel: HST/ACS [O iii ] image showing the presence of three closely separated emission peaks. We mark the position of each Sérsic component for the emission peaks as green circles. Third panel: best-fit GALFIT model, using four Sérsic components. Fourth panel: residual image after subtraction of the best-fit GALFIT model.

Table 2 lists the best-fit model parameters. The strong [O iii ] peaks of emission are fit with Sérsic components with indices 0.41 ≤ n ≤ 0.51, indicating that they are similar to Gaussians ( n = 0.5), but in two cases show a slightly more centrally concentrated distribution. Given that these components have effective radii ∼2–3 times that of an unresolved source, we opted to not include a PSF component in the fitting model, since it is not expected to significantly change the results.

Given the unique morphology of the optical emission observed in MCG-03-34-64 with HST, we examine other available multiwavelength observations (Table 1 ) to obtain a more comprehensive picture of this inner region.

3.1.2. Chandra Imaging

Figure 3 shows the inner ∼200 pc region of MCG-03-34-64, as observed with Chandra/ACIS in different energy bands. The images are binned at one-eighth of the native pixel to use the full-resolution of the instrument in the high-count inner region, and processed with 1 kernel Gaussian smoothing.

Figure 3.  Chandra/ACIS-S merged data set showing the inner 200 pc region of MCG-03-34-64 in different bands (one-eighth subpixel, and 1 kernel Gaussian smoothing). First panel: soft (0.3–3 keV) X-ray image. Second panel: 3–5 keV hard continuum image. Third panel: Fe K α (6.2–6.6 keV) Chandra image. We show the location of the two Fe K α centroids as blue circles. Fourth panel: 6–7 keV hard band Chandra image.

We measure nearly equal X-ray luminosities in the narrow 6.2–6.6 keV band from the Chandra image for both Fe K α peaks, L (6.2−6.6 keV) ∼ 3.2 ± 0.6 × 10 40 erg s −1 , for D ∼ 78 Mpc (e.g., de Grijp et al. 1992 ; Table 3 ).

Table 3.  Chandra/ACIS-S Merged Data Set—Astrometry, Fluxes, and Luminosities of the Individual Fe K α Regions

Note. The luminosities are calculated for D = 78 Mpc.

To address concerns that the dual morphology might be a spurious detection due to smoothing on scales smaller than the Chandra PSF, we examine the individual Chandra observations (prior to merging) listed in Table 1 , in the Fe K α band (Figure 4 ). These images are binned at one-eighth of the native pixel and smoothed with a 1 kernel Gaussian. As shown, the dual morphology of the Fe K α band is indeed observed in all individual observations, prior to merging, confirming the robustness of the detection. The differences in surface brightness between the individual Chandra exposures seen in Figure 4 for the individual nuclei are most likely due to statistical noise.

3.1.3. VLA Imaging

The morphology of the 8.46 GHz radio continuum emission in MCG-03-34-64 is also analyzed, and shown in Figure 5 . The positions of the two radio centroids identified by Schmitt et al. ( 2001 ) in the inner region are shown as white circles (see their Table 2). The 8.46 GHz emission starts as a linear structure at the position of the northern radio centroid, extending ∼100 pc southwestward to the central radio peak, and then bending southward in the direction of the southern [O iii ] centroid (Figure 5 ). Table 4 lists the positions and fluxes of the individual radio components, as measured in Schmitt et al. ( 2001 ). The separation between the two centroids is 116 ± 14 pc.

Figure 5.  VLA-A 8.46 GHz (3.6 cm) radio continuum image of MCG-03-34-64. White circles mark the position of the two radio peaks, and the [O iii ] centroids are shown in green. The image is shown in log scale.

Table 4.  VLA-A 3.6 cm Radio Continuum Image Decomposition—Position and Fluxes of Individual Components

Note. From Schmitt et al. ( 2001 ).

3.1.4. Astrometry Registration

We initially apply CIAO wavdetect 15 to the merged 0.3–7 keV Chandra image with a >5 σ detection threshold, detecting two faint sources near the edge of the chip array (via comparison with the Vizier source catalog). However, given their faintness, these are not suitable to use as a basis for astrometry correction.

We then create Chandra images in the narrow Fe K α band (6.2–6.6 keV), known to be dominated by nuclear emission in obscured sources (Fabbiano & Elvis 2024 ). Assuming that the radio emission in AGNs also originates from the innermost regions around the SMBH, we correct Chandra's absolute astrometry by aligning the emission peaks seen in the Fe K α band with those in the 8.46 GHz radio image. This alignment method has been used in similar studies, such as in Mrk 78 (Fornasini et al. 2022 ).

We apply a total shift of [Δx, Δy] = [0.1, 0.7] pixels to the Chandra/ACIS data, well within the absolute astrometry accuracy of the telescope. 16 Comparison with available HST observations confirms the accuracy of VLA's astrometry.

3.2. Spectroscopic Analysis

The overall spectral profile observed in the Chandra data is consistent across the earlier NuSTAR and XMM-Newton observations. All three spectra show an absorption feature at 6.8 keV, likely arising from Fe XXV absorption, and suggesting an outflow with v ∼ 5000 km s −1 , as noted in Miniutti et al. ( 2007 ). Below 3 keV, the soft X-ray emission is dominated by photoionized and collisionally ionized emission lines, from Ne, O, and Fe L ions (Miniutti et al. 2007 ).

3.2.1. XMM-Newton and NuSTAR Spectral Fitting

We proceed to model the X-ray spectrum of MCG-03-34-64 with MYTorus (Murphy & Yaqoob 2009 ), a physically motivated model built to describe the interaction of the emission from an X-ray point-source with a surrounding, and homogeneous torus of cold neutral material.

We fit the joint XMM+NuSTAR X-ray spectrum with a source model of the form:

A × TBabs × [ xstar × MYTZ × zpowerlw +( C × ( MYTS + MYTL × gsmooth )+ zpowerlaw _ soft + soft _ emiss )], where TBabs describes the absorption of emission by the Galactic column density, xstar is the photoionized absorber described previously in Miniutti et al. ( 2007 ), [ MYTZ × zpowerlw] describes the intrinsic continuum in transmission absorbed by torus, MYTS is the scattered (reflected) toroidal component off Compton-thick matter, MYTL is the associated Fe/Ni K α /K β line emission, and gsmooth accounts for some Gaussian broadening of the MYTorus line emission, where the upper limit on the line width is σ < 65 eV. The soft X-ray components are zpowerlaw _ soft , which is an unabsorbed scattered power-law component, and soft _ emiss , which is the sum of the photo and collisionally ionized emission components described by Miniutti et al. ( 2007 ). A is the cross normalization factor between NuSTAR and XMM ( A = 1.20 ± 0.05) and C is the offset between reflected/line components and intrinsic continuum components ( C is frozen at 1). The results of the fitting are shown in Figure 6 (center and right panels).

Given the quality and resolution of the X-ray observations used in this work, the spectra and fitting models employed in our analysis account for emission within the entire inner region of MCG-03-34-64, and cannot be performed separately for the individual Fe K α peaks uncovered in the Chandra imaging data. In this case, the resulting configuration suggested by MYTorus requires one where one is looking along the edge (Compton-thin line of sight) of a very Compton-thick absorber overall, which obscures both Fe K α regions.

We also note that the difference observed between the summed Fe K α luminosities derived from the Chandra imaging, ∼6.4 × 10 40 erg s −1 , and the total Fe K α luminosity yielded by the spectral fitting with MYTorus , L (6.2−6.6 keV) = 1.0 × 10 41 erg s −1 , may be attributed to line absorption by the absorber, which in turn implies a higher intrinsic X-ray luminosity, as yielded by the results of the spectral fit.

4. Discussion

The results presented in Section 3 reveal puzzling properties of the emission in MCG-03-34-64. Our imaging analysis identified three [O iii ]-emitting regions in the HST/ACS data, separated by 76 ± 8 and 79 ± 8 pc (Table 2 , Figure 2 ). In X-rays with Chandra/ACIS, two spatially resolved peaks of emission are observed in the narrow 6.2–6.6 keV Fe K α band, separated by 125 ± 21 pc (Table 3 , Figure 3 ). In the radio with VLA-A, Schmitt et al. ( 2001 ) previously identified two distinct radio cores in the 8.46 GHz continuum, separated by 116 ± 14 pc (Table 4 , Figure 5 ).

Figure 7 shows the Chandra/ACIS Fe K α image and the position of these multiwavelength centroids. The image is binned at one-eighth of the native ACIS-S pixel and smoothed with 1 kernel Gaussian.

Figure 7.  Chandra/ACIS-S merged Fe K (6.2–6.6 keV) image of MCG-03-34-64 (one-eighth subpixel, and smoothed with 1 kernel Gaussian). Optical centroids from HST/ACS are shown in red, VLA-A 8.46 GHz centroids in white, and Chandra/ACIS Fe K centroids in blue. The circle sizes reflect uncertainties in the position of the centroids.

4.1. Bolometric Luminosity

Table 5.  Joint XMM and NuSTAR Spectral Fitting Results from MYTorus

Notes. We use a correction factor k = 30 (Vasudevan & Fabian 2007 ) to obtain the integrated bolometric luminosity in X-rays.

4.1.1. HST F814W Continuum Fluxes

Our results reveal that the integrated observed fluxes are ≤3% of the integrated intrinsic flux in the band (Table 6 ), with the largest fraction originating from the central region. These fractions are consistent with scattered, hidden continuum (e.g., Pier et al. 1994 ), but could also include contributions from emission lines (e.g., Kraemer & Crenshaw 2000 ) and recombination continuum (Osterbrock & Robertis 1985 ). Therefore, it is unlikely that we will detect AGN continuum emission directly in the optical, and we cannot determine which of these regions harbors the AGN, given that all three regions are consistent with scatter continua from an active nucleus (but see below).

Table 6.  [O iii ] Luminosities Calculated from the Measured [O iii ] Fluxes from Table 2 , and Considering a Distance of D = 78 Mpc

Note We use a correction factor c = 454 (Lamastra et al. 2009 ) to calculate the bolometric luminosity in each [O iii ] region. We also show the measured F814W fluxes for each emitting region.

4.2. Multiwavelength Emission Centroids

The high fluxes and luminosities found in Section 3 for individual emission regions in the optical, X-ray, and radio bands support the presence of an AGN in this system. However, pinpointing the AGN's location is more challenging. We discuss possible interpretations for the system's configuration, based on our results and the limitations of the data.

4.2.1. Single AGN+Shocked Interstellar Medium

One interpretation is that the active nucleus is located at the position of the northern centroids ([O iii ], Fe K α , and radio; see Figure 7 ), based on the fluxes of individual components (Tables 2 , 3 , and 4 ). In this single AGN scenario, the remaining emission centroids (central Fe K α , [O iii ] and radio centroids, and southern [O iii ]) may arise from the interaction between the AGN and the interstellar medium (ISM). This would manifest as a mix of photoionized and collisionally ionized (shocked) gas from an extended NLR, similar to NGC 3393 (e.g., Maksym et al. 2016 ). Such an interpretation is consistent with previous spectral fitting results for this galaxy, which indicate a mix of photoionized and shock-ionized gas in the soft X-ray emission (Miniutti et al. 2007 ). Similarly, it is possible that the AGN in this system is located at the position of the central [O iii ], Fe K α , and radio peaks, while the remaining multiwavelength centroids may be attributed to AGN–ISM shock emission.

4.2.2. Dual AGN+Shocked ISM

Following the discussion in Section 4.2.1 , the high Fe K α luminosities (Table 3 ), and the high energies required for the production of such line emission suggest that both Fe K α regions could be powered by an active SMBH. In this scenario, the northern emission centroids would pinpoint the location of one AGN, while the central emission centroids (radio, Fe K α , and optical) may be associated with a second active SMBH in this system (given the high fluxes found for the central optical region in the F814W continuum band; Table 6 ). The distances measured between the different centroids attributed to each AGN are consistent across different wave bands (Table 7 ), supporting the dual AGN scenario.

Table 7.  Distances between Multiwavelength Centroids Found in This Work: HST/ACS, VLA-A, and Chandra/ACIS-S (Fe K α )

In this scenario, the southern [O iii ] region may arise from collisionally ionized emission in the ISM. Shock emission from jet–ISM interaction at the southern optical centroid location is supported by (1) the morphology of the radio emission at the central radio peak, which is observed to bend southward (Schmitt et al. 2001 ), in the direction of the southern [O iii ] peak (see Figures 5 and 3 , and Section 3.1.3 ); and (2) the morphology of the Chandra 0.3–3 keV (soft) emission, which is also observed to bend southward in the direction of the southern [O iii ] centroid (see Figure 3 , and Section 3.1.3 ). The lack of a corresponding southern radio or hard X-ray counterpart is consistent with the hypothesis that the northern and central [O iii ] centroids are powered by individual AGNs.

The dual AGN scenario is strengthened by the consistent values between the estimated bolometric luminosities derived from [O iii ] and X-rays (Tables 5 and 6 ), and the detection of nearly equal Fe K α emission peaks in the Chandra image, a powerful tool for identifying and confirming dual AGN systems (De Rosa et al. 2022 ). In the 3–5 keV Chandra image (Figure 3 ), the northern nucleus appears brighter than the central nucleus, although some extended emission is observed toward the central nucleus in this band. The column densities in the transmission of the two nuclei may not be the same, i.e., the AGN located at the central Fe K α region could have a higher absorbing column and appear fainter at lower energies. A higher contribution from the photoionized+thermal extended soft X-ray gas is expected at these lower energies. Given the resolution of the analyzed X-ray data, performing a separate spectral analysis of each individual Fe K α region is currently impractical.

5. Summary and Conclusions

We analyze new HST/ACS and Chandra/ACIS observations of the nearby Seyfert galaxy MCG-03-34-64, along with archival HST/ACS, XMM-Newton/Epic-pn, NuSTAR, and VLA-A data sets. Our analysis reveals the following:

In X-rays with Chandra: Two spatially resolved emission centroids are detected in the 6.2–6.6 keV Fe K α image, separated by 125 ± 21 pc. These peaks are evident in individual exposures and the merged data set. The northern and central Fe K α regions have 36 ± 6 and 37 ± 6 counts in the narrow 6.2–6.6 keV band, respectively, corresponding to ≥6 σ detections, and nearly equal Fe K α luminosities, L (6.2−6.6 keV) ∼ 3.2 ± 0.6 × 10 40 erg s −1 .

In the radio with VLA: Two emission regions are observed in the 3.6 cm VLA continuum image (Schmitt et al. 2001 ), spatially colocated with the northern and central Fe K α and [O iii ] regions.

We propose two possible physical interpretations of our results, and discuss these in the context of our analysis:

1. The "single AGN+shocked ISM" scenario, which proposes the existence of a single active nucleus in the system, while the remaining multiwavelength centroids may be attributed to the interaction of the ISM with the radio jet in the NLR.

This scenario is strengthened by:

a. Previous X-ray studies on this source, which find evidence for a mix of collisionally and photoionized X-ray gas in the NLR (Miniutti et al. 2007 ).

This scenario is challenged by:

b. The high Fe K α luminosities derived for individual regions and the energies required for the production of such line emission.

2. The "dual AGN+shocked ISM" scenario, which proposes the existence of a dual SMBH pair in this system separated by just 125 ± 21 pc.

a. The detection of two spatially resolved Fe K α regions in the Chandra imaging data, with high individual luminosities (Table 3 ).

b. The detection of three very bright and compact (<60 pc diameter) [O iii ]-emitting regions in the HST imaging data, and the respective individual bolometric luminosities (Table 6 ).

c. The detection of spatially coincident Fe K α , radio, and [O iii ] centroids at the northern and central regions. This is the first time spatially resolved, multiwavelength emission centroids in X-rays, radio, and optical are detected colocated in a nearby candidate dual AGN. For comparison, the recent study of Koss et al. ( 2023 ), which identified the presence of a dual AGN system separated by ∼230 pc in UGC 4211, detected colocated optical (HST F814W, MUSE AO [O iii ], and H α ), NIR (Keck J and K'), and submillimeter (Atacama Large Millimeter/submillimeter Array continuum at ∼230 GHz) centroids at the position of the two nuclei, but with no confirmation from X-rays or radio observations.

In summary, although we cannot definitively confirm or exclude the physical scenarios presented here, identification of the two nuclei in a deeper Chandra exposure would help to confirm a possible dual black hole system in this galaxy. Analysis of gas kinematics in the nuclear region of MCG-03-34-64 is crucial to determine the nature of the observed structures. Kinematic information obtained with HST/STIS long-slit spectroscopy could reveal disturbed kinematics expected from either the individual outflows of two SMBHs or the highly disturbed kinematics resulting from the merger environment. This information cannot be obtained from the archival X-Shooter data and requires the resolution of HST to probe the ∼100 pc region of interest.

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