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تسجيل مستخدم جديدOn the cosmological evolution of quasar black-hole masses
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Virial black-hole mass estimates are presented for 12698 quasars in the redshift interval 0.1<z<2.1, based on modelling of spectra from the Sloan Digital Sky Survey (SDSS) first data release . The black-hole masses of the SDSS quasars are found to lie between $simeq10^{7}Msun$ and an upper limit of $simeq 3times 10^{9}Msun$, entirely consistent with the largest black-hole masses found to date in the local Universe. The estimated Eddington ratios of the broad-line quasars (FWHM geq2000 km s^{-1}) show a clear upper boundary at L_{bol}/L_{Edd}~1, suggesting that the Eddington luminosity is still a relevant physical limit to the accretion rate of luminous broad-line quasars at $zleq 2$. By combining the black-hole mass distribution of the SDSS quasars with the 2dF quasar luminosity function, the number density of active black holes at $zsimeq 2$ is estimated as a function of mass. By comparing the estimated number density of active black holes at $zsimeq 2$ with the local mass density of dormant black holes, we set lower limits on the quasar lifetimes and find that the majority of black holes with mass $geq 10^{8.5}Msun$ are in place by $simeq 2$.
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