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

We present dynamical models of the nearby compact elliptical galaxy M32, using high-quality kinematic measurements, obtained with the integral-field spectrograph SAURON mounted on the William Herschel Telescope on La Palma. We also include STIS data obtained previously by Joseph et al. We find a best-fitting black hole mass of M• = (2.5 ± 0.5) × 10 6 Mand a stellar I-band mass-to-light ratio of (1.85 ± 0.15) M � /L � . For the first time, we are also able to constrain the inclination along which M32 is observed to 70 ◦ ± 5 ◦ . Assuming that M32 is indeed axisymmetric, the averaged observed flattening of 0.73 then corresponds to an intrinsic flattening of 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-fitting model and in- vestigate the effect of regularization on the orbit distribution.

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