The Siena Galaxy Atlas (SGA) is a multiwavelength, diameter-limited atlas of nearby galaxies built using the DESI Legacy Imaging Surveys (the Legacy Surveys). For each galaxy, the SGA delivers precise coordinates, multiwavelength mosaics, azimuthally averaged surface-brightness and color profiles, integrated and aperture photometry, and additional metadata. Because large, resolved galaxies trace the foreground extragalactic sky, the SGA also serves as a foundational reference catalog for wide-field cosmological surveys such as the Dark Energy Spectroscopic Instrument (DESI).

The SGA-2020 was released in January 2021 and contains 383,620 galaxies selected primarily from the HyperLeda extragalactic database. It is built on deep grz optical imaging from the Legacy Surveys Data Release 9 (DR9) and all-sky mid-infrared imaging at 3.4–22 microns from unWISE (W1–W4).

SGA-2025 expands the atlas to nearly 500,000 galaxies across approximately 30,000 deg² of the extragalactic sky using the Legacy Surveys DR11. It adds i-band optical mosaics, GALEX near- and far-ultraviolet (NUV/FUV) imaging, and a richer suite of surface-brightness profiles and photometric measurements, making it the most complete census of large, resolved galaxies to date.

The SGA and SGAML Jupyter kernels set three environment variables with NERSC defaults:

SGA_DIR=/dvs_ro/cfs/cdirs/cosmo/work/legacysurvey/sga/2025
SGA_DATA_DIR=/dvs_ro/cfs/cdirs/cosmo/data/sga/2025/data
SGA_HTML_DIR=/dvs_ro/cfs/cdirs/cosmo/work/legacysurvey/sga/2025/html

To override any of these — or to point a kernel at a working branch — create ~/.sga_dev_env; it is sourced by both kernels at startup, after the defaults are set:

# ~/.sga_dev_env — sourced by both SGA and SGAML kernels at startup
export PATH=/global/homes/i/ioannis/code/SGA/bin/SGA2025:$PATH
export PYTHONPATH=/global/homes/i/ioannis/code/SGA/py:$PYTHONPATH
export SGA_DATA_DIR=/pscratch/sd/i/ioannis/SGA2025-v1.6

Any variable set here takes precedence over the kernel defaults. Delete or empty the file to revert to the installed environment.

We gratefully acknowledge funding support for this work from the National Science Foundation under grants AST-1616414 and AST-1909374, and the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Award Number DE-SC0020086.