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.

[1]  D. Merritt.  Dynamical mapping of hot stellar systems , 1993 .

[2]  Ortwin Gerhard,et al.  Line-of-sight velocity profiles in spherical galaxies: breaking the degeneracy between anisotropy and mass , 1993 .

[3]  Charles L. Lawson,et al.  Solving least squares problems , 1976, Classics in applied mathematics.

[4]  P. T. de Zeeuw,et al.  Galaxy Mapping with the SAURON Integral-Field Spectrograph: The Star Formation History of NGC 4365 , 2000, astro-ph/0011254.

[5]  M. Schwarzschild,et al.  A numerical model for a triaxial stellar system in dynamical equilibrium , 1979 .

[6]  Tod R. Lauer,et al.  M33: A Galaxy with No Supermassive Black Hole , 2001, astro-ph/0107135.

[7]  H. Bender.  Highly homologous cyclodextrin glycosyltransferases from Bacillus circulans strain 8 and a strain of Bacillus licheniformis , 1990, Applied Microbiology and Biotechnology.

[8]  Herwig Dejonghe,et al.  A completely analytical family of anisotropic Plummer models , 1987 .

[9]  O. Gerhard.  A new family of distribution functions for spherical galaxies , 1991 .

[10]  Roeland P. van der Marel,et al.  accepted for publication in The Astrophysical Journal Supplements Axisymmetric Three-Integral Models for Galaxies , 1999 .

[11]  The Orbital Structure and Potential of NGC 1399 , 1999, astro-ph/9909446.

[12]  J. Tonry.  Evidence for a central mass concentration in M32 , 1984 .

[13]  R. Bender,et al.  The Nuclear Dynamics of M32. I. Data and Stellar Kinematics , 2000, astro-ph/0005530.

[14]  E. Verolme,et al.  Two-integral Schwarzschild models , 2001, astro-ph/0112185.

[15]  J. Bruijne,et al.  Scale-free dynamical models for galaxies : flattened densities in spherical potentials , 1996, astro-ph/9601044.

[16]  B. Madore,et al.  The distance to M31 from infrared photometry of its cepheids , 1986 .

[17]  R. Carlberg,et al.  The Velocity and Mass Distribution of Clusters of Galaxies from the CNOC1 Cluster Redshift Survey , 1999, astro-ph/9910494.

[18]  M. Cappellari.  Efficient multi-Gaussian expansion of galaxies , 2002, astro-ph/0201430.

[19]  A. Dressler,et al.  Constraints on the mass distribution near the centers of M31 and M32 , 1990 .

[20]  The stellar dynamics of M87 , 1996, astro-ph/9610112.

[21]  M. Cappellari,et al.  The Counterrotating Core and the Black Hole Mass of IC 1459 , 2002, astro-ph/0202155.

[22]  H. Rix,et al.  Velocity profiles of galaxies with claimed black holes — I. Observations of M31, M32, NGC 3115 and NGC 4594 , 1994 .

[23]  S. Tremaine,et al.  Maximum-entropy models of galaxies , 1988 .

[24]  E. Emsellem,et al.  The SAURON project — II. Sample and early results , 2002 .

[25]  O. Gerhard,et al.  Dynamics of the boxy elliptical galaxy NGC 1600 , 1999, astro-ph/9901036.

[26]  J. Tonry.  A central black hole in M32 , 1987 .

[27]  Alan Dressler,et al.  Stellar dynamics in the nuclei of M31 and M32 - evidence for massive black holes , 1988 .

[28]  Martin Schwarzschild,et al.  Triaxial equilibrium models for elliptical galaxies with slow figure rotation , 1982 .

[29]  HongSheng Zhao.  A steady-state dynamical model for the COBE-detected Galactic bar , 1996 .

[30]  W. Dehnen,et al.  Three-integral models of oblate elliptical galaxies , 1993 .

[31]  C. Lawson,et al.  Solving least squares problems , 1976, Classics in applied mathematics.

[32]  R. Davies,et al.  The SAURON project – I. The panoramic integral-field spectrograph , 2001, astro-ph/0103451.

[33]  H. Rix,et al.  Velocity profiles of galaxies with claimed black holes – II. f (E, Lz) models for M32 , 1994 .

[34]  S. Tremaine,et al.  Axisymmetric, Three-Integral Models of Galaxies: A Massive Black Hole in NGC 3379 , 1999, astro-ph/9912026.

[35]  Hans-Walter Rix,et al.  Dynamical Modeling of Velocity Profiles: The Dark Halo around the Elliptical Galaxy NGC 2434 , 1997 .

[36]  H. Rix,et al.  2 Hubble Fellow. , 1997 .

[37]  Breaking the degeneracy between anisotropy and mass: the dark halo of the E0 galaxy NGC 6703 , 1997, astro-ph/9710129.

[38]  T. Lauer,et al.  Planetary camera observations of the central parsec of M32 , 1992 .

[39]  M. Franx,et al.  A new method for the identification of non-Gaussian line profiles in elliptical galaxies , 1993 .

[40]  Ralf Bender,et al.  The Demography of massive dark objects in galaxy centers , 1997, astro-ph/9708072.

[41]  Evidence for a Massive Black Hole in the S0 Galaxy NGC 4342 , 1998, astro-ph/9805324.

[42]  William H. Press,et al.  Numerical recipes , 1990 .

[43]  P. T. de Zeeuw,et al.  Improved Evidence for a Black Hole in M32 from HST/FOS Spectra. II. Axisymmetric Dynamical Models , 1997, astro-ph/9705081.

[44]  P. D. Zeeuw,et al.  Observable properties of the power-law galaxies. , 1994 .

[45]  H. Dejonghe,et al.  The Three-Dimensional Mass Distribution in NGC 1700 , 1998, astro-ph/9810046.