Astrophysical Journal Formatting Requirements: Complete Author Guide

ApJ follows AAS conventions for abstracts.

• Word limit: 250 words for Regular Articles, 150 words for Letters
• Structure: Unstructured (single paragraph)
• Citations: Not typically included (AAS style discourages abstract citations)
• Math: LaTeX equations in the abstract are acceptable

The abstract should state the scientific question, describe the data or methods, and present the main results. Astronomy abstracts routinely include specific numerical results: distances, velocities, temperatures, luminosities, masses. "We detect a transit signal with a depth of 0.8% and derive a planetary radius of 1.3 R_Earth" is standard.

Keywords: ApJ uses the Unified Astronomy Thesaurus (UAT) for keywords. During submission, you select keywords from the UAT rather than providing free-text keywords. The UAT is a controlled vocabulary maintained by the AAS. Select 3-6 UAT concepts that best describe your paper's content.

This keyword system is different from most other journals. You can browse the UAT at astrothesaurus.org before submission to identify the best terms for your paper.

ApJ has well-established figure standards, and the astronomy community generally produces high-quality publication figures.

Figure specifications:

Figure best practices in astronomy:

• Multi-panel figures are very common (4-panel, 6-panel, even 16-panel grids)
• Label axes clearly with units
• Use colorbar legends for heat maps and images
• For spectral plots, label emission/absorption lines directly
• For sky images, include a scale bar and compass (N/E orientation)

Machine-readable tables (MRTs): This is ApJ's most distinctive formatting requirement. Large data tables (more than a few rows of data) must be submitted in machine-readable format.

MRT specifications:

• Plain text format with fixed-width columns
• Standardized header with column descriptions, units, and data types
• Byte-by-byte format description
• Submitted alongside the paper and published in the article
• Deposited in the CDS/VizieR database for community access

The MRT format is unfamiliar to most first-time ApJ authors. AAS provides tools and documentation for creating MRTs, and the AASTeX template includes commands for generating them. A typical MRT might contain photometric measurements, spectral line parameters, or catalog entries for hundreds or thousands of objects.

Small tables (fewer than roughly 10-15 rows) can use standard LaTeX table format. But any table that represents a dataset rather than a summary should be in MRT format.

Table formatting for standard tables:

• Every column must have a header with units
• Use \tablehead and \startdata/\enddata in AASTeX
• Notes below tables using \tablenotetext
• Table title above using \tablecaption

ApJ uses the AAS author-year reference style. This is different from the numbered systems used by ACS, Elsevier, and Wiley journals.

In-text citations: Author-year format.

• One author: (Smith 2024) or Smith (2024)
• Two authors: (Smith & Jones 2024) or Smith & Jones (2024)
• Three or more authors: (Smith et al. 2024) or Smith et al. (2024)

Reference list format (alphabetical by first author):

Smith, A. B., Jones, C. D., & Williams, E. F. 2024, ApJ, 950, 123

Key formatting details:

• Author names: Last name, initials (Smith, A. B.)
• Ampersand before last author
• Year after the author list
• Journal abbreviation (ApJ, MNRAS, A&A, etc.)
• Volume number, then page or article number
• DOIs encouraged but not always listed (ADS links serve this function in astronomy)
• arXiv preprints cited with eprint number

Astronomy has a unique referencing culture because of the NASA Astrophysics Data System (ADS). BibTeX entries for virtually every astronomy paper are available on ADS, and most astronomers build their .bib files by exporting directly from ADS. If you do this, the formatting is automatically correct.

Use the aasjournal.bst BibTeX style file, which comes with AASTeX. It handles all AAS formatting conventions, including the distinctive journal abbreviation macros (\apj, \mnras, \aap, etc.).

There's no reference cap. Published ApJ papers typically cite 30-60 references, but survey papers and reviews can cite 100+.

AAS journals have a well-developed system for supplementary data products, reflecting astronomy's culture of data sharing.

Types of supplementary content:

1. Figure sets: If you have many similar figures (e.g., spectra of 50 objects), AASTeX supports "figure sets" where the full set is published online but only representative examples appear in the printed article.

1. Machine-readable tables: Large data tables published in MRT format (described above).

1. Animations and videos: Supported for online publication. Use standard formats (MP4, GIF).

1. Data behind figures: AAS encourages authors to provide the data underlying each figure as supplementary material.

1. Supplemental text and appendices: Extended derivations, additional analysis, and supporting material.

Data hosting: AAS provides data hosting through the journal's online infrastructure. Large datasets can also be deposited in discipline-specific repositories (MAST, IRSA, NED, CDS/VizieR).

Data availability: ApJ requires that all data used in the paper be available to readers. This can be through supplementary files, public archives, or explicit data sharing statements.

The astronomy community has strong norms around data sharing. ApJ papers routinely include links to reduced data products, code repositories (GitHub, Zenodo), and archival data. If you don't provide access to your data, reviewers will ask for it.

ApJ uses the AAS submission portal at journals.aas.org.

Required components:

• Manuscript source files (.tex, .bib, figure files, MRT files)
• Compiled PDF
• Cover letter (optional but recommended for Letters)

AAS-specific requirements:

• Software citations: AAS strongly encourages citing all software used in the analysis. Use the \software{} command in AASTeX. This is increasingly important and reviewers will note missing software citations.
• Data availability: State where all data can be accessed.
• Object names: Use standard nomenclature from SIMBAD/NED. AASTeX's \objectname{} command creates database links.
• ORCID iDs: Encouraged for all authors.

arXiv posting: Like PRB, ApJ has no embargo policy regarding arXiv. Most astronomy papers appear on arXiv simultaneously with or before journal submission. This is standard practice and expected in the field.

These are the details that experienced ApJ authors know:

AASTeX is not optional in practice. While AAS accepts other formats, the entire production pipeline is built around AASTeX. Using it avoids delays and formatting issues during production.

Machine-readable tables are enforced. If your paper contains a large data table in standard LaTeX format, you'll be asked to convert it to MRT format during review or production. Do it before submission.

Author-year citations, not numbered. Astronomy uses author-year style while most other physical sciences use numbered citations. If you're submitting to ApJ from a physics or chemistry background, switch your citation style.

Journal abbreviation macros. AASTeX includes macros for common journal names (\apj, \apjl, \apjs, \mnras, \aap, \aj, \pasp, etc.). Use them. They ensure consistent abbreviations and look correct in the typeset output.

Software and data citations. AAS has been a leader in promoting software and data citation. Your paper should cite the specific versions of software packages used (e.g., astropy, numpy, matplotlib). These citations go in a separate "Software" section or in the Acknowledgments.

Page charges are real but voluntary. The per-page charge system is unique to AAS journals. You'll receive an invoice after acceptance. Payment is voluntary and doesn't affect publication, but most institutions pay.

Astronomical nomenclature. Use standard naming conventions from the IAU. Don't invent new names for objects. Refer to existing catalogs (2MASS, Gaia DR3, SDSS, etc.) using standard designators.

Figures of merit. Astronomy papers frequently report uncertainties, and ApJ expects them to be presented correctly. Use symmetric errors (5.2 +/- 0.3) or asymmetric errors (5.2 +0.4/-0.2). State confidence intervals explicitly (1-sigma, 3-sigma, 95%).

These trip up ApJ authors:

1. Machine-readable tables. First-time ApJ authors almost always submit large tables in standard LaTeX format and get asked to convert them. Learn the MRT format before submission.

1. UAT keywords. ApJ uses the Unified Astronomy Thesaurus, not free-text keywords. Browse the UAT before submission.

1. Software citations. Increasingly required. List all significant software packages with version numbers.

1. AASTeX version. Use v6.3+, not older versions. Earlier AASTeX versions are missing current features and formatting options.

1. Journal abbreviation macros. Use the built-in macros (\apj, \mnras, etc.) rather than typing abbreviations manually. This ensures consistency.