In Search of the Largest Velocity Dispersion Galaxies

We present Hobby-Eberly Telescope (HET) observations for galaxies at redshift z < 0.3 from the Sloan Digital Sky Survey (SDSS) showing large velocity dispersions while appearing to be single galaxies in HST images. The high signal-to-noise HET spectra provide more definitive velocity dispersions. The maximum velocity dispersion we find is σ* = 444 km s−1. Emission-line widths in QSOs indicate that black holes can exist with masses M• exceeding 5 billion M☉, implying σ* > 500 km s−1 by the local M•-σ* relationship. This suggests either that QSO black hole masses are overestimated or that the black hole-bulge relationship changes at high black hole mass. The latter option is consistent with evidence that the increase in σ* with luminosity levels off for the brightest elliptical galaxies.