H I properties of satellite galaxies around local volume hosts

We present neutral atomic hydrogen (H I) observations using the Robert C. Byrd Green Bank Telescope along the lines of sight to 49 confirmed or possible dwarf satellite galaxies around eight Local Volume systems (M104, M51, NGC 1023, NGC 1156, NGC 2903, NGC 4258, NGC 4565, and NGC 4631). We detect the H I reservoirs of two candidates (dw0934+2204 and dw1238−1122) and find them to be background sources relative to their nearest foreground host systems. The remaining 47 satellite candidates are not detected in H I, and we place stringent 5σ upper limits on their H I mass. We note that some (15/47) of our non-detections stem from satellites being occluded by their putative host’s H I emission. In addition to these new observations, we compile literature estimates on the H I mass for an additional 17 satellites. We compare the H I properties of these satellites to those within the Local Group, finding broad agreement between them. Crucially, these observations probe a ‘transition’ region between −10 ≳ M_V ≳ −14 where we see a mixture of gas-rich and gas-poor satellites. While there are many gas-poor satellites within this region, some are gas-rich and this suggests that the transition towards predominantly gas-rich satellites occurs at L_V ∼ 10⁷L_☊, in line with simulations. The observations presented here are a key step toward characterizing the properties of dwarf satellite galaxies around Local Volume systems and future wide-field radio surveys with higher angular resolution (e.g. WALLABY) will vastly improve upon the study of such systems.