Distance and mass of the M104 (Sombrero) group

Abstract: Distances and radial velocities of galaxies in the vicinity of the luminous early-type galaxy M 104 (Sombrero) are used to derive its dark matter mass. Two dwarf galaxies: UGCA 307 and KKSG 30 situated near M 104 were observed with the Advanced Camera for Surveys on the Hubble Space Telescope. The distances $9.03^{+0.84}_{-0.51}$ Mpc (UGCA 307) and $9.72^{+0.44}_{-0.41}$ Mpc (KKSG 30) were determined using the tip of the red giant branch method. These distances are consistent with the dwarf galaxies being satellites of Sombrero. Using radial velocities and projected separations of UGCA 307, KKSG 30, and a third galaxy with an accurate distance (KKSG 29), as well as 12 other assumed companions with less accurate distances, the total mass of M 104 is estimated to be $(1.55\pm0.49) 10^{13} M_{\odot}$. At the K-band luminosity of the Sombrero galaxy of $2.4 10^{11} L_{\odot}$, its total mass-to-luminosity ratio is $M_T/L_K = (65\pm20)M_{\odot}/L_{\odot}$, which is about three times higher than that of luminous bulgeless galaxies.