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

Abstract

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 $10^{9.5}<M_{\star ,\text{host}}<10^{10.5}{\text{M}}_{\odot }$ at redshifts $0.07<z<0.09$, all selected to be central galaxies. Merian's medium-band imaging isolates H$\alpha$ and [O \textsc{iii}] emission lines for galaxies in this redshift range, enabling efficient selection of star-forming satellites down to $M_{\star ,\text{sat}}\gtrsim 10^{7.5}{\text{M}}_{\odot }$. 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 $148\pm 7$ satellite candidates associated with the host sample. We find that $\sim 60\%$ of hosts have $N_{\mathrm{sat}}<1$ massive satellites within their virial radii, $\sim 22\%$ have $1\le N_{\mathrm{sat}}<2$, $\sim 10\%$ have $2\le N_{\mathrm{sat}}<3$, and $\sim 8\%$ have $N_{\mathrm{sat}}>3$. 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.

arXiv comment12 pages, 7 figures, 1 appendix, submitted to ApJ