A SAURON study of M32: measuring the intrinsic flattening and the central black hole mass

Abstract

We present dynamical models of the nearby compact elliptical galaxy M32, using high quality kinematical measurements, obtained with the integral-field spectrograph SAURON mounted on the William Herschel Telescope on La Palma. We also include STIS data obtained by Joseph et al. We find a best-fit black hole mass of (2.5 +/- 0.5) million solar masses and a stellar I-band mass-to-light ratio of (1.85 +/- 0.15) in solar units. For the first time, we are also able to constrain the inclination along which M32 is observed to (70 +/- 5) degrees. Combined with an averaged observed flattening of 0.73, this corresponds to an intrinsic flattening of approximately 0.68 +/- 0.03. These tight constraints are mainly caused by the use of integral-field data. We show this quantitatively by comparing with models that are constrained by multiple slits only. We show the phase-space distribution and intrinsic velocity structure of the best-fit model and investigate the effect of regularisation on the orbit distribution.