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[*] 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

[*] Citations to 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, marel@stsci.edu.
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