Distance and mass of the M 104 (Sombrero) group

Abstract

Aims: 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.
Methods: 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_-0.51^+0.84 Mpc (UGCA 307) and 9.72_-0.41^+0.44 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.
Results: 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 ± 0.49) × 10¹³ M_⊙. At the K-band luminosity of the Sombrero galaxy of 2.4 × 10¹¹ L_⊙, its total mass-to-luminosity ratio is M_T/L_K = (65 ± 20) M_⊙/L_⊙, which is about three times higher than that of luminous bulgeless galaxies.