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Register a new userThe relationship between radio luminosity and black-hole mass in optically-selected quasars
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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.
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We investigate the relationship between the mass of the central supermassive black hole, M_bh, and the host galaxy luminosity, L_gal, in a sample of quasars from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). We use composite quasar spectra binned by black hole mass and redshift to assess galaxy features that would otherwise be overwhelmed by noise in individual spectra. The black hole mass is calculated using the photoionization method, and the host galaxy luminosity is inferred from the depth of the Ca II H + K features in the composite spectra. We evaluate the evolution in the M_bh - L_gal relationship by examining the redshift dependence of Delta log M_bh, the offset in black hole mass from the local black hole - bulge relationship. There is little systematic trend in Delta log M_bh out to z = 0.8. Using the width of the [O III] emission line as a proxy for the stellar velocity dispersion, sigma_*, we find agreement of our derived host luminosities with the locally-observed Faber-Jackson relation. This supports the utility of the width of the [O III] line as a proxy for sigma_* in statistical studies.
A sample of 103 quasars from the Large Bright Quasar Survey (LBQS) has been observed with the VLA at 8.4 GHz to study the evolution of the radio luminosity distribution and its dependence on absolute magnitude. Radio data from pointed observations are now available for 359 of the 1055 LBQS quasars. The radio-loud fraction is constant at ~10% over the absolute magnitude range -28 <= MB <= -23, and it rises to ~20% (log R > 1) or ~35% (log L > 25) at the brightest absolute magnitudes in the sample. This nearly flat distribution differs markedly from those of the optically selected Palomar-Green (PG) Bright Quasar Survey and the X-ray selected Extended Medium Sensitivity Survey (EMSS), both of which have lower radio-loud fractions for absolute magnitudes fainter than MB = -24 and higher fractions at brighter magnitudes. The reason for the high radio-loud fraction at bright absolute magnitudes in the PG, compared to the LBQS and other optically selected quasar surveys, is unknown. The trend of increasing radio-loud fraction with absolute magnitude in the EMSS is due at least in part to a correlation between X-ray and radio luminosity. Combining the LBQS data with radio studies of high-redshift quasars leads to the conclusion that the radio-loud fraction in optically selected quasars does not appear to evolve significantly, aside from a modest increase at z ~1, from z = 0.2 to redshifts approaching 5, a result that is contrary to previous studies which found a decrease in radio-loud fraction with increasing redshift by comparing the low-z fraction in the PG to higher redshift samples.
We describe a correlation between the mass M_BH of a galaxys central black hole and the luminosity-weighted line-of-sight velocity dispersion sigma_e within the half-light radius. The result is based on a sample of 26 galaxies, including 13 galaxies with new determinations of black hole masses from Hubble Space Telescope measurements of stellar kinematics. The best-fit correlation is M_BH = 1.2 (+-0.2) x 10^8 M_sun (sigma_e/200 km/s)^(3.75 (+-0.3))over almost three orders of magnitude in M_BH; the scatter in M_BH at fixed sigma_e is only 0.30 dex and most of this is due to observational errors. The M_BH-sigma_e relation is of interest not only for its strong predictive power but also because it implies that central black hole mass is constrained by and closely related to properties of the host galaxys bulge.
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.
We have investigated the relationship between the 2-10 keV X-ray variability amplitude and black hole mass for a sample of 46 radio-quiet active galactic nuclei observed by ASCA. Thirty-three of the objects in our sample exhibited variability over a time-scale of ~40 ks, and we found a significant anti-correlation between excess variance and mass. Unlike most previous studies, we have quantified the variability using nearly the same time-scale for all objects. Moreover, we provide a prescription for estimating the uncertainties in excess variance which accounts both for measurement uncertainties and for the stochastic nature of the variability. We also present an analytical method to predict the excess variance from a model power spectrum accounting for binning, sampling and windowing effects. Using this, we modelled the variance-mass relation assuming all objects have a universal twice-broken power spectrum, with the position of the breaks being dependent on mass. This accounts for the general form of the relationship but there is considerable scatter. We investigated this scatter as a function of the X-ray photon index, luminosity and Eddington ratio. After accounting for the dependence of excess variance on mass, we find no significant correlation with either luminosity or X-ray spectral slope. We do find an anti-correlation between excess variance and the Eddington ratio, although this relation might be an artifact owing to the uncertainties in the mass measurements. It remains to be established that enhanced X-ray variability is a property of objects with steep X-ray slopes or large Eddington ratios.
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