Luminosity Functions and Host-to-host Scatter of Dwarf Satellite Systems in the Local Volume

Low-mass satellites around Milky Way (MW)-like galaxies are important probes of small-scale structure and galaxy formation. However, confirmation of satellite candidates with distance measurements remains a key barrier to fast progress in the Local Volume (LV). We measure the surface brightness fluctuation distances to recently cataloged candidate dwarf satellites around 10 massive hosts within D < 12 Mpc to confirm association. The satellite systems of these hosts are complete and mostly cleaned of contaminants down to M-g similar to -9 to -10, within the area of the search footprints. Joining this sample with hosts surveyed to comparable or better completeness in the literature, we explore how well cosmological simulations combined with common stellar to halo mass relations (SHMR) match observed satellite luminosity functions in the classical satellite luminosity regime. Adopting an SHMR that matches hydrodynamic simulations, we find that the predicted overall satellite abundance agrees well with the observations. The MW is remarkably typical in its luminosity function among LV hosts. We find that the host-to-host scatter predicted by the model is in close agreement with the scatter between the observed systems, once the different masses of the observed systems are taken into account. However, we find significant evidence that the observed systems have more bright and fewer faint satellites than the SHMR model predicts, possibly necessitating a higher normalization of the SHMR around halo masses of 10(11) M or significantly greater scatter than present in common SHMRs. These results demonstrate the utility of nearby satellite systems in inferring the galaxy-subhalo connection in the low-mass regime.