We are using STIS spectra to derive the masses of 5 hypermassive black holes (HMBHs). From the observed scaling relations defined by less massive spheroids, these objects are expected to reside at the nuclei of host galaxies with stellar velocity dispersions greater than 320 km/s, i.e., at the very massive limits on the evolution of galaxies. These 5 targets have confirmed regular gas distributions on the scales of the black hole sphere of influence. It is essential that the sphere of influence is resolved for accurate determinations of black hole mass (0.1"). These scales cannot be effectively observed from the ground.
Only the masses of two HMBHs have been modeled so far. It is impossible to draw any general conclusions about the connections between HMBH mass and their massive host galaxies, i.e., place limits on the evolution of galaxies. With these 5 targets we will determine whether these HMBHs deviate from the scaling relations defined by less massive spheroids. A larger sample will allow us to firmly anchor the high mass end of the correlation between black hole mass and stellar velocity dispersion, and other scaling relations. Therefore, we are also conducting a SNAPSHOT program with the hope of detecting a further 24 HMBH candidates for STIS observation in future cycles. At the completion of this project we will have populated the high mass end of the scaling relations with the sample sizes enjoyed by less massive spheroids, and have placed important constraints on the limits of the evolution of galaxies.