Supermassive black holes in bulges

We present spatially extended gas kinematics at parsec-scale resolution for the nuclear regions of four nearby disk galaxies and model them as rotatio n of a gas disk in the joint potential of the stellar bulge and a putative central black hole. The targets were selected from a larger set of long-sli t spectra obtained with the Hubble Space Telescope as part of the Survey of Nearby Nuclei with STIS. They represent the four galaxies (of 24) that dis play symmetric gas velocity curves consistent with a rotating disk. We deri ve the stellar mass distribution from the STIS acquisition images adopting the stellar mass-to-light ratio normalized to match ground-based velocity d ispersion measurements over a large aperture. Subsequently, we constrain th e mass of a putative black hole by matching the gas rotation curve, followi ng two distinct approaches. In the most general case we explore all the pos sible disk orientations; alternatively, we constrain the gas disk orientati on from the dust-lane morphology at similar radii. In the latter case the k inematic data indicate the presence of a central black hole for three of th e four objects, with masses of 10(7)-10(8) M., representing up to similar t o0.025% of the host bulge mass. For one object (NGC 2787) the kinematic dat a alone provide clear evidence for the presence of a central black hole eve n without external constraints on the disk orientation. These results illus trate directly the need to determine black hole masses by differing methods for a large number of objects, demonstrate that the variance in black hole /bulge mass is much larger than previously claimed, and reinforce the recen t finding that the black hole mass is tightly correlated with the bulge ste llar velocity dispersion sigma.