Shadows in the Dark: Low-Surface-Brightness Galaxies Discovered in the Dark Energy Survey

Abstract

We present a catalog of 23,790 extended low-surface-brightness galaxies (LSBGs) identified in $\sim 5000\hat{A}{°}^2$ from the first three years of imaging data from the Dark Energy Survey (DES). Based on a single-component Sérsic model fit, we define extended LSBGs as galaxies with $g$-band effective radii $R_{eff}(g)>2.5^{\prime \prime }$ and mean surface brightness $\bar{\hat{I}}{¼}_{eff}(g)>24.2mag\grave{E}\S rcse{c}^{-2}$. We find that the distribution of LSBGs is strongly bimodal in $(g-r)$ vs.\ $(g-i$) color space. We divide our sample into red ($g-i\ge 0.60$) and blue ($g-i<0.60$) galaxies and study the properties of the two populations. Redder LSBGs are more clustered than their blue counterparts and are correlated with the distribution of nearby ($z<0.10$) bright galaxies. Red LSBGs constitute $\sim 33\%$ of our LSBG sample, and $\sim 30\%$ of these are located within 1 deg of low-redshift galaxy groups and clusters (compared to $\sim 8\%$ of the blue LSBGs). For nine of the most prominent galaxy groups and clusters, we calculate the physical properties of associated LSBGs assuming a redshift derived from the host system. In these systems, we identify 41 objects that can be classified as ultra-diffuse galaxies, defined as LSBGs with projected physical effective radii $R_{eff}>1.5kpc$ and central surface brighthness $\hat{I}{¼}_0(g)>24.0magarcse{c}^{-2}$. The wide-area sample of LSBGs in DES can be used to test the role of environment on models of LSBG formation and evolution.

31 pages, 19 figures. Version accepted for publication in ApJS. Data products related to this work can be found in: https://des.ncsa.illinois.edu/releases/other/y3-lsbg