Abstract
The broad emission lines commonly seen in quasar spectra have velocity widths of a few per cent of the speed of light, so special- and general-relativistic effects have a significant influence on the line profile. We have determined the redshift of the broad H-beta line in the quasar rest frame (determined from the core component of the [OIII] line) for over 20,000 quasars from the Sloan Digital Sky Survey DR7 quasar catalog. The mean redshift as a function of line width is approximately consistent with the relativistic redshift that is expected if the line originates in a randomly oriented Keplerian disk that is obscured when the inclination of the disk to the line of sight exceeds ~30-45 degrees, consistent with simple AGN unification schemes. This result also implies that the net line-of-sight inflow/outflow velocities in the broad-line region are much less than the Keplerian velocity when averaged over a large sample of quasars with a given line width.
Highlights
Quasars and other active galactic nuclei (AGNs) are accreting supermassive black holes (BHs)
We present a simple treatment of relativistic effects on the spectrum of the broad-line region (BLR), and use kinematic properties of the broad line to constrain the geometry of the BLR, assuming that the gas is in a steady state and that its kinematics are determined by the gravitational field of the central BH (“virialized”)
Using data from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) quasar catalog, we have argued that the mean redshift in quasar BLRs is largely due to relativistic effects
Summary
Quasars and other active galactic nuclei (AGNs) are accreting supermassive black holes (BHs). The line widths are believed to arise from Doppler shifts, typically thousands of km s−1, due to orbital motion of the gas in the gravitational field of the BH, and/or large-scale inflows or outflows This general picture is supported by measurements of the BLR size through reverberation mapping (RM; see, e.g., Peterson et al 2004; Bentz et al 2009). We present a simple treatment of relativistic effects on the spectrum of the BLR, and use kinematic properties of the broad line (centroid velocity shift and line width) to constrain the geometry of the BLR, assuming that the gas is in a steady state and that its kinematics are determined by the gravitational field of the central BH (“virialized”). We use the large spectroscopic quasar sample from the Sloan Digital Sky Survey (SDSS; Schneider et al 2010), which allows us to average out object-to-object measurement errors and variations in line profile
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