2025MNRAS.536.2072C

We report the spectroscopic analysis of 10 satellite galaxy candidates in the sphere of influence of the Sombrero galaxy (M104, NGC4594), based on data obtained with IFUM (integral field units for Magellan). Based on their newly observed recessional velocities, we confirm that nine of these candidates are satellite galaxies of M104, with one being a background dwarf galaxy. All 10 dwarfs have stellar masses $2\times 10^{7}$ to $1\times 10^{9}\, {\rm M}_{\odot }$ and mean weighted metallicities $-1.7\lt \langle {[\mathrm{M/H}]}\rangle \lt -0.3$. Although these dwarfs are predominantly old, with stellar populations $\sim 5{\!-\!}11\,$ Gyr. However, this sample contains a local example of a low-mass 'green pea' candidate, it exhibits extreme optical emission features and broad emission line features ($\sigma \sim 250\, \mathrm{km\, s^{-1}}$) reminiscent of high-redshift Ly $\alpha$/Ly C photon leaking galaxies. Using the newly acquired recessional velocities of the nine satellites of M104, we find no evidence of coherent satellite motions unlike other nearby $L_*$ galaxy environments. Given the small sample, this result does not statistically rule out such coherent motions. There remain 60 satellite candidates of M104 for which future spectroscopy can more reliably test for such motion. Using the observed dwarf galaxies as tracers of the gravitational potential of M104, we estimate the dynamical mass of M104, $M_{\rm dyn}=(12.4\pm 6.5)\times 10^{12}\,{\rm M}_{\odot }$, and find that, making a reasonable estimate of M104's gas mass, $\gt 90$ per cent of its baryons are missing. These results agree with previous measurements of M104's dynamical mass.