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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.
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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.
In order to investigate the dependence of quasar variability on fundamental physical parameters like black hole mass, we have matched quasars from the QUEST1 Variability Survey with broad-lined objects from the Sloan Digital Sky Survey. The matched sample contains approximately 100 quasars, and the Sloan spectra are used to estimate black hole masses and bolometric luminosities. Variability amplitudes are measured from the QUEST1 light curves. We find that black hole mass correlates with several measures of the variability amplitude at the 99% significance level or better. The correlation does not appear to be caused by obvious selection effects inherent to flux-limited quasar samples, host galaxy contamination or other well-known correlations between quasar variability and luminosity/redshift. We evaluate variability as a function of rest-frame time lag using structure functions, and find further support for the variability--black hole mass correlation. The correlation is strongest for time lags of the order a few months up to the QUEST1 maximum temporal resolution of approximately 2 years, and may provide important clues for understanding the long-standing problem of the origin of quasar optical variability. We discuss whether our result is a manifestation of a relation between characteristic variability timescale and black hole mass, where the variability timescale is typical for accretion disk thermal timescales, but find little support for this. Our favoured explanation is that more massive black holes have larger variability amplitudes, and we highlight the need for larger samples with more complete temporal sampling to test the robustness of this result.
Using a sample of more than 6000 quasars from the Sloan digital sky survey (SDSS) we compare the black-hole mass distributions of radio-loud and radio-quiet quasars. Based on the virial black-hole mass estimator the radio-loud quasars (RLQs) are found to harbour systematically more massive black holes than radio-quiet quasars (RQQs) with very high significance (>>99.99%), with mean black-hole masses of <log(M_{bh}/Msun)>=8.89pm0.02 and <log(M_{bh}/Msun)>=8.69pm0.01 for the RLQs and RQQs respectively. Crucially, the new RLQ and RQQ samples have indistinguishable distributions on the redshift-optical luminosity plane, excluding the possibility that either parameter is responsible for the observed black-hole mass difference. Moreover, this black-hole mass difference is shown to be in good agreement with the optical luminosity difference observed between RLQ and RQQ host galaxies at low redshift (i.e. Delta M_{host}=0.4-0.5 magnitudes). Within the SDSS samples, black-hole mass is strongly correlated with both radio luminosity and the radio-loudness $mathcal{R}$ parameter (>7 sigma significance), although the range in radio luminosity at a given black-hole mass is several orders of magnitude. It is therefore clear that the influence of additional physical parameters or evolution must also be invoked to explain the quasar radio-loudness dichotomy.
Mergers of spinning black holes can give recoil velocities from gravitational radiation up to several thousand km/s. A recoiling supermassive black hole in an AGN can retain the inner part of its accretion disk, providing fuel for continuing AGN activity. Using AGN in the Sloan Digital Sky Survey (SDSS) that show velocity shifts of the broad emission lines relative to the narrow lines, we place upper limits on the incidence of high velocity recoils in AGN. Brief but powerful flares in soft X-rays may occur when bound material falls back into the moving accretion disk.
We propose a new method of estimation of the black hole masses in AGN based on the normalized excess variance, sigma_{nxs}^2. We derive a relation between sigma_{nxs}^2, the length of the observation, T, the light curve bin size, Delta t, and the black hole mass, assuming that (i) the power spectrum above the high frequency break, f_{bf}, has a slope of -2, (ii) the high frequency break scales with black hole mass, (iii) the power spectrum amplitude (in frequency x power space) is universal and (iv) sigma_{nxs}^2 is calculated from observations of length T < 1/f_{bf}. Values of black hole masses in AGN obtained with this method are consistent with estimates based on other techniques such as reverberation mapping or the Mbh-stellar velocity dispersion relation. The method is formally equivalent to methods based on power spectrum scaling with mass but the use of the normalized excess variance has the big advantage of being applicable to relatively low quality data.
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