Systematically Measuring Ultra Diffuse Galaxies (SMUDGes). I. Survey
  Description and First Results in the Coma Galaxy Cluster and Environs
  We present a homogeneous catalog of 275 large (effective radius $\gtrsim$ 5.3
arcsec) ultra-diffuse galaxy (UDG) candidates lying within an $\approx$ 290
square degree region surrounding the Coma cluster. The catalog results from our
automated postprocessing of data from the Legacy Surveys, a three-band imaging
survey covering 14,000 square degrees of the extragalactic sky. We describe a
pipeline that identifies UDGs and provides their basic parameters. The survey
is as complete in these large UDGs as previously published UDG surveys of the
central region of the Coma cluster. We conclude that the majority of our
detections are at roughly the distance of the Coma cluster, implying effective
radii $\ge 2.5$ kpc, and that our sample contains a significant number of
analogs of DF 44, where the effective radius exceeds 4 kpc, both within the
cluster and in the surrounding field. The $g-z$ color of our UDGs spans a large
range, suggesting that even large UDGs may reflect a range of formation
histories. A majority of the UDGs are consistent with being lower stellar mass
analogs of red sequence galaxies, but we find both red and blue UDG candidates
in the vicinity of the Coma cluster and a relative overabundance of blue UDG
candidates in the lower density environments and the field. Our eventual
processing of the full Legacy Surveys data will produce the largest, most
homogeneous sample of large UDGs.
