Constraining the quasar population with the broad-line width distribution

Stephen Fine, Scott Croom, P Hopkins, L Hernquist, Joss Bland-Hawthorn, Matthew Colless, P Hall, L Miller, Adam Myers, Robert Nichol, Kevin Pimbblet, Nic Ross, Donald Schneider, Tom Shanks, Robert Sharp

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In this work, we test the assertion that the scatter in the mass of black holes which drive quasars should be luminosity dependent with less scatter in more luminous objects. To this end, we measure the width of the Mg ii I>2799 line in quasar spectra from the Sloan Digital Sky Survey (SDSS), 2df QSO Redshift survey (2QZ) and 2dF SDSS LRG And QSO (2SLAQ) surveys and, by invoking an unnormalized virial mass estimator, relate the scatter in linewidth to the scatter of mass in the underlying black hole population. We find conclusive evidence for a trend such that there is less scatter in linewidth, and hence black hole mass, in more luminous objects. However, the most luminous objects in our sample show such a low degree of scatter in linewidth that, when combined with measures for the intrinsic scatter in the radius-luminosity relation for the broad-line region (BLR) in active galaxies, an inconsistency arises in the virial technique for estimating black hole masses.
Original languageEnglish
Pages (from-to)1413 - 1429
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 2008
Externally publishedYes

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