Improved Evidence for a 3 × 10[TSUP]6[/TSUP] [ITAL]M[/ITAL][TINF]⊙[/TINF] Black Hole in M32: Canada-France-Hawaii Telescope Spectroscopy with FWHM = 0[farcs]47 Resolution

Abstract

We present improved spectroscopy of M32 with the Canada-France-Hawaii Telescope and Subarcsecond Imaging Spectrograph. Tip-tilt guiding provides a resolution of FWHM = 047 or σ_* = 020 (σ_* = Gaussian dispersion radius of the point-spread function). The observed central velocity dispersion, σ 92 ± 5 km s^-1, and the maximum rotation velocity, V_max = 55 ± 3 km s^-1, are larger than at lower resolution. In addition, the measured line-of-sight velocity distributions indicate the possible presence of broad wings at radii r 02, with significant numbers of stars at ΔV 200 km s^-1 from the mean velocity. Two-integral dynamical models fit these data provided that M32 contains a central dark object, probably a black hole, of mass M_• (3.0 ± 0.5) × 10⁶ M_☉. This confirms detections based on lower resolution spectra by Tonry, Dressler, Richstone, van der Marel, Dehnen, and collaborators. The available spatial resolution has now improved by a factor of 3 since Tonry's discovery observations; each improvement in resolution has strengthened the case for a black hole in M32.