Orbit-based dynamical models of the Sombrero Galaxy (NGC4594)

Abstract

We present axisymmetric, orbit-based models to study the central black hole (BH), stellar mass-to-light ratio (M/L), and dark matter (DM) halo of NGC4594 (M104, the Sombrero Galaxy). For stellar kinematics, we use published high-resolution kinematics of the central region taken with the Hubble Space Telescope, newly obtained Gemini long-slit spectra of the major axis, and integral field kinematics from the Spectroscopic Areal Unit for Research on Optical Nebulae instrument. At large radii, we use globular cluster kinematics to trace the mass profile and apply extra leverage to recovering the DM halo parameters. We find a BH of mass M • = (6.6 ± 0.4) × 108 M ⊙ and determine the stellar M/L I = 3.4 ± 0.05 (uncertainties are the 68% confidence band marginalized over the other parameters). Our best-fit DM halo is a cored logarithmic model with asymptotic circular speed Vc = 376 ± 12 km s-1 and core radius rc = 4.7 ± 0.6kpc. The fraction of dark to total mass contained within the half-light radius is 0.52. Taking the bulge and disk components into account in our calculation of σe puts NGC4594 squarely on the M-σ relation. We also determine that NGC4594 lies directly on the M-L relation. © 2011. The American Astronomical Society. All rights reserved.