QSO Narrow [OIII] Line Width and Host Galaxy Luminosity

Abstract

Galaxy bulge luminosity L, black hole mass (Mbh), and stellar velocity dispersion (sigma_*) increase together in a way suggesting a close evolutionary relationship. Measurements of the Mbh-sigma_* relationship as a function of cosmic time may shed light on the origin of this relationship. Direct measurements of sigma_* at high redshift are difficult, and the width of the narrow emission lines of AGN has been proposed as a surrogate. We investigate the utility of using sigma_[OIII] for sigma_* by examining host galaxy magnitudes and [OIII] line widths for low redshift QSOs. For radio-quiet QSOs, sigma_[OIII] is consistent in the mean with the value of sigma_* predicted by the Faber-Jackson relation. For our limited range of host luminosity, scatter obscures the expected increase of sigma_[OIII] with host luminosity. However, for a sample of AGN covering a wide range of measured or inferred sigma_*, there is a clear increase of sigma_[OIII] with sigma_*. Radio-loud QSOs on average have sigma_* smaller by ~0.1 dex than radio-quiet QSOs of similar host luminsotiy, at least for luminosities typical of PG QSOs. Star formation rates in our low redshift QSOs are smaller than required to maintain the typical observed ratio of bulge mass to black hole mass.