IMPROVED EVIDENCE FOR A 3 X 10~6 SOLAR MASS BLACK HOLE IN M32: CANADA-FRANCE-HAWAII TELESCOPE SPECTROSCOPY WITH FWHM = 0.47″ RESOLUTION

摘要

We present improved spectroscopy of M32 with the Canada-France-Hawaii Telescope and Subarcsecond Imaging Spectrograph. Tip-tilt guiding provides a resolution of FWHM = 0.47″ or σ_* = 0.20″ (σ_* = Gaussian dispersion radius of the point-spread function). The observed central velocity dispersion, σ approx= 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 approx< 0.2″, with significant numbers of stars at ΔV approx= 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_· approx= (3.0 ± 0.5) X 10~6 solar mass. This confirms detections based on lower resolution spectra by Tonry, Dressier, 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.