HI-bearing ultra-diffuse ALFALFA galaxies

We select sources from ALFALFA with surface brightnesses, magnitudes, and radii consistent with other samples of ultra-diffuse galaxies (UDGs) without restrictions on their isolation or environment, more than doubling the previously reported ALFALFA sample.

We quantify the galactic environment of HUDs using several metrics, including n^th^ nearest neighbour, tidal influence, membership in a group/cluster, and distance from nearest group/cluster or filament. We find that HUDs inhabit the same environments as other samples of HI-selected galaxies and that they show no environmental preference in any metric. We suggest that these results are consistent with a picture of the extreme properties of HUDs being driven by internal mechanisms and that they are largely unperturbed by environmental impacts.