Neutral Hydrogen Clouds in the M81/M82 Group

We have observed a $3^{\circ} \times 3^{\circ}$ area centered on the M81/M82 group of galaxies using the Robert C. Byrd Green Bank Telescope (GBT) in a search for analogs to the High Velocity Clouds (HVCs) of neutral hydrogen found around our galaxy. The velocity range from -605 to -85 km s$^{-1}$ and 25 to 1970 km s$^{-1}$ and over the inner $2^{\circ} \times 2^{\circ}$ the 7$\sigma$ detection threshold of $9.6 \times 10^{5} M_{\odot}$. We detect 5 previously unknown \hone clouds associated with the group, as well as numerous associated filamentary \hone structures, all lying in the range $-140 \leq V_{helio} \leq +240$ km s$^{-1}$. From the small angular distance of the clouds to group members, and the small velocity difference between group members and clouds, we conclude that the clouds are most likely relics of ongoing interactions between galaxies in the group.

The result of the observation, flagging, calibration and image processing is a 3x3 degree calibrated FITS cube. This cube is fully calibrated, including atmospheric attenuation (adopted tau = 0.009) and a GBT efficiency model. The data are presented in units of Jy/Beam.