Beyond the brim of the hat: Kinematics of globular clusters out to large radii in the sombrero galaxy

Abstract

We have obtained radial velocity measurements for 51 new globular clusters around the Sombrero galaxy. These measurements were obtained using spectroscopic observations from the AAOmega spectrograph on the Anglo-Australian Telescope and the Hydra spectrograph at WIYN. Combining our own past measurements and velocity measurements obtained from the literature, we have constructed a large database of radial velocities that contains a total of 360 confirmed globular clusters. Previous studies' analyses of the kinematics and mass profile of the Sombrero globular cluster system have been constrained to the inner 9′ (24 kpc or 5Re ), but our new measurements have increased the radial coverage of the data, allowing us to determine the kinematic properties of M104 out to 15′ (41 kpc or 9Re ). We use our set of radial velocities to study the GC system kinematics and to determine the mass profile and V-band mass-to-light profile of the galaxy. We find that M/LV increases from 4.5 at the center to a value of 20.9 at 41 kpc (9Re or 15′), which implies that the dark matter halo extends to the edge of our available data set. We compare our mass profile at 20 kpc (4Re or 7.′4) to the mass computed from X-ray data and find good agreement. We also use our data to look for rotation in the globular cluster system as a whole, as well as in the red and blue subpopulations. We find no evidence for significant rotation in any of these samples.