2019ApJ...880...30H

Ultra-diffuse galaxies are objects that have very extended morphology and faint central surface brightness. Most UDGs are discovered in galaxy clusters and groups, but some are also found in low-density environments. The diffuse morphology and faint surface brightness make them difficult to distinguish from the sky background. Several previous works have suggested that at least some UDGs are consistent with exponential surface brightness profiles). The surface brightness of exponential disks is enhanced in edge-on systems, so searching for edge-on systems may be an efficient way to select UDGs. In this paper, we focus on searching for edge-on H I-bearing ultra-diffuse sources (HUDS) from the 40% Arecibo Legacy Fast ALFA (ALFALFA) catalog, based on Sloan Digital Sky Survey g- and r-band images. After correcting the observed central surface brightness to a face-on perspective, we discover 11 edge-on HUDS candidates. All these newly discovered HUDS candidates are blue and H I-bearing, similar to other HUDS in 70% ALFALFA catalog, and different from UDGs in clusters.