The Siena Galaxy Atlas (SGA) is a compilation of data from three surveys completed between 2014 and 2017 known as the DESI Legacy Surveys, which were carried out to identify galaxy targets for the Dark Energy Spectroscopic Instrument (DESI) survey. The data were collected at Cerro Tololo Inter-American Observatory and Kitt Peak National Observatory, both Programs of NSF’s NOIRLab, and at the University of Arizona’s Steward Observatory. The atlas also contains data from a survey by NASA’s Wide-field Infrared Survey Explorer (WISE) satellite.
Optical mosaics of 42 galaxies from the SGA-2020 sorted by increasing angular diameter from the top-left to the bottom-right. Galaxies are chosen randomly from a uniform (flat) probability distribution in angular diameter. The horizontal white bar in the lower-left corner of each panel represents 1 arcminute and the mosaic cutouts range from 3.2 to 13.4 arcminutes. This figure illustrates the tremendous range of types, sizes, colors and surface brightness profiles, internal structure, and environments of the galaxies in the SGA. Image credit: CTIO / NOIRLab / DOE / NSF / AURA / J. Moustakas.
“Nearby large galaxies are important because we can study them in more detail than any other galaxies in the Universe; they are our cosmic neighbors,” said Siena College’s Professor John Moustakas, SGA project leader.
“Not only are they strikingly beautiful, but they also hold the key to understanding how galaxies form and evolve, including our very own Milky Way Galaxy.”
The new atlas builds on several centuries of efforts to chart the night skies.
The iconic Catalogue des Nébuleuses et des Amas d’Étoiles (Catalogue of Nebulae and Star Clusters), published in 1774 by French astronomer Charles Messier, was a major milestone, as was the New General Catalogue of Nebulae and Clusters of Stars (NGC), published in 1888 by John Louis Emil Dreyer.
More recently, in 1991, astronomers assembled the Third Reference Catalog of Bright Galaxies (RC3).
Several other valuable galaxy atlases have been published over the past two decades, but most of them draw on the photographic-plate measurements in the RC3, or are missing significant numbers of galaxies.
Since the SGA uses digital images captured with highly sensitive instruments, it represents a substantial improvement in both data quality and completeness.
“Previous galaxy compilations have been plagued by incorrect positions, sizes and shapes of galaxies, and also contained entries which were not galaxies but stars or artifacts,” said Dr. Arjun Dey, an astronomer at NOIRLab.
“The SGA cleans all this up for a large part of the sky. It also provides the best brightness measurements for galaxies, something we have not reliably had before for a sample of this size.”
This versatile resource will drive progress in numerous branches of astronomy and astrophysics by helping scientists find the best galaxy samples for targeted observation.
For example, the SGA will enhance research into how patterns of star formation vary across different galaxies, the physical processes underlying the diverse array of morphologies that galaxies display, and how the distribution of galaxies is related to how dark matter is spread across the Universe.
By acting as a map, the SGA will also help astronomers pinpoint the sources of transient signals like gravitational waves and understand the events that give rise to them.
“The SGA is going to be the pre-eminent digital galaxy atlas for large galaxies,” Dr. Dey said.
“However, the SGA is not just for academic researchers, it is freely available to view online for anyone wishing to get to know our corner of the Universe better.”
“In addition to its scientific utility, it has a lot of pictures of beautiful galaxies!”
“The public release of these spectacular data contained in the atlas will have a real impact not only on astronomical research, but also on the public’s ability to view and identify relatively nearby galaxies,” said Dr. Chris Davis, NSF Program Director for NOIRLab.
“Dedicated amateur astronomers will particularly love this as a go-to resource for learning more about some of the celestial targets they observe.”
