The Merian Survey: A Statistical Census of Bright Satellites of Sub-Milky Way-Mass Galaxies

Satellite populations provide sensitive tests of the galaxy-halo connection, but studies have largely focused on Milky Way (MW)-mass host galaxies or a small number of nearby dwarf galaxy hosts. Here we present a statistical census of bright, star-forming satellite galaxies around sub-MW-mass hosts using the first data release of the Merian Survey. Our sample consists of 357 hosts with stellar mass 10 9.5<M, host<10 10.5 M at redshifts 0.07<z<0.09, all selected to be central galaxies. Merian's medium-band imaging isolates H α and [O iii] emission lines for galaxies in this redshift range, enabling efficient selection of star-forming satellites down to M, sat 10 7.5, M. We identify 471 satellite candidates within the projected virial radii of these hosts. After statistically subtracting the contribution from foreground and background galaxies, we find 148 plus or minus 7 satellite candidates associated with the host sample. We find that 60% of hosts have N sat< 1 massive satellites within their virial radii, 22% have 1 at most N sat< 2, 10% have 2 at most N sat< 3, and 8% have N sat > 3. Satellite abundance increases with host stellar mass across the sub-MW regime, extending the observed trend from dwarf to MW-mass galaxies and broadly agreeing with predictions from the TNG50 simulation. The radial distribution of satellites around sub-MW-mass hosts is similar to that around MW-mass hosts and broadly consistent with TNG50. Together, these results extend our empirical view of satellite populations across the previously sparsely sampled transition between dwarf and MW-mass hosts.