We have found the atomic gas ( \ion H1 ) reservoirs of the blue ultra diffuse galaxy ( UDG ) candidates identified by Róman 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 \ion H1 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 \ion H1 mass – stellar mass plane is consistent with that of the broader gas-rich galaxy population , and both their \ion H1 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 \ion H1 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 .