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R. F. Green, G. A. Bower (NOAO/KPNO), STIS Team
NGC 4486B is a dwarf companion to M 87. Its projected separation is 7.3\arcmin, or 34 kpc. The radial velocity difference is only some 200 km/s, suggesting that NGC 4486B may be bound to M 87. Lauer et al.~showed from their WFPC2 images that NGC 4486B has a double nucleus reminiscent of that in M 31, and a disk-like central distribution of stars. The two peaks are separated by 10-13 pc, are closely matched in central surface brightness, lie at comparable distances from the photocenter, but do not comprise a distinct nuclear component. NGC 4486B is unique among dwarf galaxies with MB = -17 mag in containing a resolved core. Kormendy et al.~analyzed long-slit spectra from the SIS spectrograph on CFHT. They found fairly rapid central rotation and a steep velocity dispersion gradient. Their model with isotropic velocity dispersion required a central dark mass of 6 \times 108 \ M\odot. This object is a significant outlier in the Faber-Jackson relation and the black hole mass - bulge mass relationship, perhaps due to tidal truncation.
The superior angular resolution of STIS allows a more detailed look at the kinematics of the nuclear region. In particular, we examine the impact of resolution on the measured peak of velocity dispersion and rotation, and on the possible detection of asymmetry in both the velocity dispersion and rotational velocity across the nucleus. The new data will ultimately place stronger constraints on anisotropic models, which currently allow solutions without a central black hole.