- [*] Gas Kinematics and the Black Hole Mass at the Center of the
Radio Galaxy NGC 4335
- Verdoes Kleijn G., van der Marel R.P., de Zeeuw P.T.,
Noel-Storr J., Baum S.A.
- AJ, 124, 2524-2542, 2002
this paper in the ADS
We investigate the kinematics of the central gas disk of the
radio-loud elliptical galaxy NGC 4335, derived from HST/STIS long-slit
spectroscopic observations of H_alpha+[NII] along 3 parallel slit
positions. The observed mean velocities are consistent with a rotating
thin disk. We model the gas disk in the customary way, taking into
account the combined potential of the galaxy and a putative black hole
with mass M_bh, as well as the influence on the observed kinematics of
the point spread function and finite slit width. This sets a 3-sigma
upper limit of 10^8 solar masses on M_bh. The velocity dispersion at r
< 0.5 arcsec is in excess of that predicted by the thin rotating disk
model. This does not invalidate the model, if the excess dispersion is
caused by localized turbulent motion in addition to bulk circular
rotation. However, if instead the dispersion is caused by the BH
potential then the thin disk model provides an underestimate of
M_bh. A BH mass M_bh = 6 x 10^8 solar masses is inferred by modeling
the central gas dispersion as due to an isotropic spherical
distribution of collisionless gas cloudlets. The stellar kinematics
for NGC 4335 are derived from a ground-based (WHT/ISIS) long-slit
observation along the galaxy major axis. A two-integral model of the
stellar dynamics yields M_bh = 3 x 10^9 solar masses. However, there
is reason to believe that this model overestimates M_bh.
Reported correlations between black hole mass and inner stellar
velocity dispersion sigma predict M_bh to be 5.4 x 10^8 solar masses
in NGC 4335. If our standard thin disk modeling of the gas kinematics
is valid, then NGC 4335 has an unusually low M_bh for its velocity
dispersion. If, on the other hand, this approach is flawed, and
provides an underestimate of M_bh, then black hole masses for other
galaxies derived from HST gas kinematics with the same assumptions
should be treated with caution.
In general, a precise determination of the M_bh - sigma relation and
its scatter will benefit from (i) joint measurements of M_bh from gas
and stellar kinematics in the same galaxies and (ii) a better
understanding of the physical origin of the excess velocity dispersion
commonly observed in nuclear gas disks of elliptical galaxies.
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Last modified November 24, 2002.
Roeland van der Marel,