Rp. Vandermarel et al., VELOCITY PROFILES OF GALAXIES WITH CLAIMED BLACK-HOLES .2. F(E, L(Z))MODELS FOR M32, Monthly Notices of the Royal Astronomical Society, 271(1), 1994, pp. 99-117
The galaxy M32 has been claimed to contain a massive central black hol
e. A major uncertainity in the existing models for M32 is the absence
of observational constraints on the dynamical structure and velocity d
ispersion anisotropy. Here we determine such constraints for the first
time. We recently measured kinematical quantities and line-of-sight v
elocity profile shapes for M32 along five different slit positions (Pa
per I). We construct axisymmetric dynamical models with distribution f
unctions of the form f(E, L(z)) for these data. Such models have sigma
(R) = sigma(z), and are flattened by an excess of azimuthal motion. We
explore two approaches, one based on a set of constant mass-to-light
ratio 'power-law' models recently discussed by Evans, the other based
on the moment equations of the collisionless Boltzmann equation. In th
e latter approach we take into account the central surface brightness
cusp observed with the HST, and we include a central black hole. We co
mpare the even and the odd parts of the observed and predicted velocit
y profiles separately, and derive independent information on the parts
of the distribution function that are even and odd in L(z), respectiv
ely. Models with f(E, L(z)) and no central black hole cannot fit the o
bserved central peak in the rms line-of-sight velocity and the steep c
entral rotation velocity gradient. A good fit to the data in the centr
al arcsec is obtained when M32 is assumed to have a central black hole
with mass M(BH) almost-equal-to 1.8 x 10(6) M(.). The major axis rota
tion velocity of M32 is approximately 90 per cent of that of a maximal
ly streaming f(E, L(z)) model. Outside the central arcsec, most of the
data are remarkably well fitted by the f(E, L(z)) models, with two ex
ceptions. First, the even parts of the observed major axis velocity pr
ofiles are slightly more flat-topped than is predicted by the models.
Secondly, the models predict too much mean streaming on the intermedia
te axis (major +/- 45-degrees), relative to the major axis. So, both t
he even and the odd parts of the distribution function of M32 must in
fact depend on a third integral of motion. Our models indicate that M3
2 most likely has a velocity distribution with upsilon(phi)2BAR > upsi
lon(theta)2BAR greater-than-or-similar-to upsilon(r)2BAR outside of th
e central arcsec. Our models are more realistic than most previous mod
els in that they take proper account of flattening, rotation and veloc
ity profile data. Yet the models still require the presence of a massi
ve central black hole. To fit the M32 data without a black hole requir
es a radially anisotropic velocity distribution in the outer region. T
he measured excess of azimuthal motion outside the central arcsec is n
ot inconsistent with this picture. However, the required excess of rad
ial motion in the central region may be implausible, given that the ce
ntral two-body relaxation time in the absence of a central black hole
is a factor approximately 10(2) shorter than the Hubble time.