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The Siena Galaxy Atlas now catalogs 400,000 nearby galaxies

Georgina Torbet
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The universe is vast, likely containing trillions of galaxies — an almost incomprehensible number. But when we focus in on just the nearby galaxies to our Milky Way, we already see a large number and huge diversity of galaxies around us.

A nearby galaxy catalog, the Siena Galaxy Atlas (SGA), was recently updated and now includes almost 400,000 galaxies located within our cosmic neighborhood, and this treasure trove of data is available to the public for free.

A galactic collision of two galaxies which began more than 300 million years ago, NGC 520 is actually made up of two disk galaxies which will eventually merge together to form one larger, more massive system. NGC 520 was discovered by William Herschel in 1784 and is one of the largest and brightest galaxies in the Siena Galaxy Atlas.
A galactic collision of two galaxies that began more than 300 million years ago, NGC 520 is actually made up of two disk galaxies that will eventually merge together to form one larger, more massive system. NGC 520 was discovered by William Herschel in 1784 and is one of the largest and brightest galaxies in the Siena Galaxy Atlas. CTIO/NOIRLab/DOE/NSF/AURA Acknowledgments: PI: J. Moustakas (Siena College) Image Procesing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab) & M. Zamani (NSF’s NOIRLab) & D. de Martin (NSF’s NOIRLab)

The data for the atlas comes from a set of surveys completed between 2014 and 2017, called the DESI Legacy Surveys. These used ground-based telescopes located in Chile and Arizona, including the Dark Energy Camera and others, to plot out the locations of galaxies spread across almost half of the night sky using both optical and infrared wavelengths.

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“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 SGA project leader John Moustakas in a statement. “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.”

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.
Optical mosaics of 42 galaxies from the Siena Galaxy Atlas-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. CTIO/NOIRLab/DOE/NSF/AURA/J. Moustakas

While there are plenty of projects looking at nearby galaxies, such as the Hubble Space Telescope project to image every known nearby galaxy, this atlas aims to provide consistent, accurate information across a massive range of hundreds of thousands of nearby galaxies.

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“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,” NOIRLab astronomer Arjun Dey explained. “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.”

The researchers hope that the atlas will not only be useful for professional astronomers and scientists who are looking for a particular type of galaxy for their research, but also for amateur astronomers and enthusiastic stargazers who want to learn about what they are seeing through their telescopes.

“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 Chris Davis, National Science Foundation 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.”

A paper about the atlas is published in The Astrophysical Journal and the data is available on the SGA website.

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Georgina Torbet
Georgina Torbet
Space Writer
Georgina is the Digital Trends space writer, covering human space exploration, planetary science, and cosmology. She…
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