The Luminosity Functions and Redshift Evolution of Satellites of
  Low-Mass Galaxies in the COSMOS Survey
  The satellite populations of the Milky Way, and Milky-Way-mass galaxies in
the local universe, have been extensively studied to constrain dark-matter and
galaxy-evolution physics. Recently, there has been a shift to studying
satellites of hosts with stellar masses between that of the Large Magellanic
Cloud and the Milky Way, since they can provide further insight on hierarchical
structure formation, environmental effects on satellites, and the nature of
dark-matter. Most work is focused on the Local Volume, and little is still
known about low-mass host galaxies at higher red-shift. To improve our
understanding of the evolution of satellite populations of low-mass hosts, we
study satellite galaxy populations as a function of host stellar mass $9.5 <
\log(M_*/M_\odot) < 10.5$ and redshifts $0.1 < z < 0.8$ in the COSMOS survey,
making this the first study of satellite systems of low-mass hosts across half
the age of the universe. We find that the satellite populations of low-mass
host galaxies, which we measure down to satellite masses equivalent to the
Fornax dwarf spheroidal satellite of the Milky Way, remain mostly unchanged
through time. We observe a weak dependence between host stellar mass and number
of satellites per host, which suggests that the stellar masses of the hosts are
in the power-law regime of the stellar mass to halo mass relation
$(M_*-M_{\text{halo}})$ for low-mass galaxies. Finally, we test the
constraining power of our measured cumulative luminosity function to calculate
the low-mass end slope of the $M_*-M_\text{halo}$ relation. These new satellite
luminosity function measurements are consistent with ${\Lambda}$CDM
predictions.
