Orbit-Based Dynamical Models of the Sombrero Galaxy (NGC 4594)
  We present axisymmetric, orbit-based models to study the central black hole,
stellar mass-to-light ratio, and dark matter halo of NGC 4594 (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 SAURON instrument. At large radii, we use globular cluster
kinematics to trace the mass profile and apply extra leverage to recovering the
dark matter halo parameters. We find a black hole of mass M_{\bullet}=(6.6 +/-
0.4) x 10^8 M_{\odot}, 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 dark matter halo is a cored logarithmic model with
asymptotic circular speed V_c=376 +/- 12 km/s and core radius r_c= 4.7 +/- 0.6
kpc. 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 \sigma_e puts NGC 4594 squarely on the M-\sigma relation. We also determine
that NGC 4594 lies directly on the M-L relation.
