We report on a study that finds a positive correlation between black hole mass and variability amplitude in quasars. Roughly 100 quasars at z<0.75 were selected by matching objects from the QUEST1 Variability Survey with broad-lined objects from the
Sloan Digital Sky Survey. Black hole masses were estimated with the virial method using the broad Hbeta line, and variability was characterized from the QUEST1 light curves. The correlation between black hole mass and variability amplitude is significant at the 99% level or better and does not appear to be caused by obvious selection effects inherent to flux-limited samples. It is most evident for rest frame time lags of the order a few months up to the QUEST1 maximum temporal resolution of about 2 years. The correlation between black hole mass and variability amplitude means that the more massive black holes have larger percentage flux variations. Over 2-3 orders of magnitude in black hole mass, the amplitude increases by approximately 0.2 mag. A likely explanation for the correlation is that the more massive black holes are starving and produce larger flux variations because they do not have a steady inflow of gaseous fuel. Assuming that the variability arises from changes in the accretion rate Li & Cao [8] show that flux variations similar to those observed are expected as a consequence of the more massive black holes having cooler accretion disks.
In order to investigate the dependence of quasar optical-UV variability on fundamental physical parameters like black hole mass, we have matched quasars from the QUEST1 variability survey with broad-lined objects from the SDSS. Black hole masses and
bolometric luminosities are estimated from Sloan spectra, and variability amplitudes from the QUEST1 light curves. Long-term variability amplitudes (rest-frame time scales 0.5--2 yrs) are found to correlate with black hole mass at the 99% significance level or better. This means that quasars with larger black hole masses have larger percentage flux variations. Partial rank correlation analysis shows that the correlation cannot explained by obvious selection effects inherent to flux-limited samples. We discuss whether the correlation is a manifestation of a relation between BH mass and accretion disk thermal time scales, or if it is due to changes in the optical depth of the accretion disk with black hole mass. Perhaps the most likely explanation is that the more massive black holes are starving, and produce larger flux variations because they do not have a steady inflow of gaseous fuel.
We have investigated the influence of nuclear parameters such as black hole (BH) mass and photoionizing luminosity on the FRI/FRII transition in a sample of nearby (z<0.2) 3CR radio galaxies. The sample was observed with medium-resolution, optical sp
ectroscopy and contains some galaxies with unpublished velocity dispersion measurements and emission-line fluxes. Measured velocity dispersions are 130-340 km/s with a mean of 216 km/s. Converting to BH mass, we find that the BH mass distribution is identical for FRIs and FRIIs, with a mean of approximately 2.5x10^8 Msun. We convert [OII] and [OIII] emission-line luminosities to photoionizing luminosity under the assumption that the gas is ionized by the nuclear UV continuum. Most of the galaxies with FRI morphology and/or low-excitation emission-line spectra have progressively lower BH masses at lower photoionizing (and jet) luminosities. This agrees with the Ledlow-Owen relation which states that the radio luminosity at the FRI/FRII transition depends on the optical luminosity of the host, L_radio ~ L_optical^1.8, because both L_radio and L_optical relate to AGN nuclear parameters. When recasting the Ledlow-Owen relation into BH mass versus photoionizing and jet luminosity, we find that the recasted relation describes the sample quite well. The FRI/FRII transition occurs at approximately an order of magnitude lower luminosity relative to the Eddington luminosity than the soft-to-hard transition in X-ray binaries. This difference is consistent with the Ledlow-Owen relation, which predicts a weak BH mass dependence in the transition luminosity. We conclude that the FRI/FRII dichotomy is caused by a combination of external and nuclear factors, with the latter dominating.
