Selections from 2018: A New Dim Galaxy Found


Editor’s note: In these last two weeks of 2018, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

Discovery of a Low-Surface-Brightness Galaxy in the NGC 2655 Field

Published January 2018

Main takeaway:

NGC 2655 field

In the field pictured in the top panel, NGC 2655 is the large galaxy that lies near the bottom left. The red crosshairs indicate the location of the new low-surface-brightness galaxy. Bottom panels show confirmation data and a FITS-cutout from the Pan-STARRS1 Surveys. [Adapted from Steiling and Crowson 2018]

A new low-surface-brightness galaxy has been found within the same field as the lenticular galaxy NGC 2655. This discovery was made by Frederick Steiling and followed up by Dan Crowson, both amateur astronomers and members of the Astronomical Society of Eastern Missouri. The new, dim galaxy is located about 22 arcminutes from NGC 2655.

Why it’s interesting:

The last few years has marked a boom in the discovery of extremely dim, faint, diffuse galaxies. By definition, these bodies are at least one magnitude lower in surface brightness than the ambient night sky; they have very few stars and are generally more than 95% non-baryonic dark matter by mass. This makes them excellent laboratories for exploring the properties of dark matter and dark-matter dominated galaxies.

What else we might learn:

Most low-surface-brightness galaxies are isolated, not lying near any other major galaxies. This has been used as an explanation for why they are so faint: without interactions with other galaxies to trigger star formation, they’ve stayed relatively dark. The newly discovered galaxy, on the other hand, does not appear to be isolated: it lies near the NGC 2655 group of galaxies, a group thought to have recently undergone interactions or mergers. If the low-surface-brightness galaxy is a part of the group (as opposed to appearing nearby by coincidence, which is also a possibility), this unusual association could teach us more about the behavior of diffuse galaxies.


Frederick Steiling and Dan Crowson 2018 Res. Notes AAS 2 11. doi:10.3847/2515-5172/aabf92