Shadows In The Dark: Low-Surface-Brightness Galaxies Discovered In The Dark Energy Survey

We present a catalog of 23,790 extended low-surface-brightness galaxies (LSBGs) identified in similar to 5000 deg(2) from the first three years of imaging data from the Dark Energy Survey (DES). Based on a single-component Sersic model fit, we define extended LSBGs as galaxies with g-band effective radii R-eff (g) > 2.'' 5 and mean surface brightness (mu) over bar (eff)(g) > 24.2 mag arcsec(-2). We find that the distribution of LSBGs is strongly bimodal in (g-r) versus (g-i) color space. We divide our sample into red (g-i >= 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 similar to 33% of our LSBG sample, and similar to 30% of these are located within 1 degrees of low-redshift galaxy groups and clusters (compared to similar to 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 ultradiffuse galaxies, defined as LSBGs with projected physical effective radii R-eff > 1.5 kpc and central surface brightness mu(0) g > 24.0 mag arcsec(-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.