Atomic Gas in Blue Ultra Diffuse Galaxies around Hickson Compact Groups
  We have found the atomic gas (HI) reservoirs of the blue ultra diffuse galaxy
(UDG) candidates identified by R\'oman and Trujillo in images near Hickson
Compact Groups (HCGs). We confirm that all of the objects are indeed UDGs with
effective radii R_e > 1.5 kpc. Three of them are likely to be gravitationally
bound to the HCG near which they project, one is plausibly gravitationally
bound to the nearest HCG, and one is in the background. We measure HI masses
and velocity widths for each object directly from the spectra, and use the
widths together with the UDG effective radii to estimate dynamical masses and
halo spin parameters. The location of the blue UDGs in the HI mass - stellar
mass plane is consistent with that of the broader gas-rich galaxy population,
and both their HI masses and gas richnesses are correlated with their effective
radii. The blue UDGs appear to be low-mass objects with high-spin halos,
although their properties are not as extreme as those of the faintest diffuse
objects found in HI searches. The data presented here highlight the potential
of single-dish radio observations for measuring the physical properties of blue
diffuse objects detected in the optical.
