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B. J. Wills, Zhaohui Shang (University of Texas at Austin)
Luminous QSOs, powered by accretion onto supermassive black holes, reach their peak space density by redshifts 2-3. They have faded by the present epoch, but their black hole relics are discovered in nearby massive galaxies. Because the masses of these local black holes are found to be proportional to galaxy bulge masses, the evolutional of QSOs and galaxies must be closely linked. To understand this evolution it is important to measure M\rm BH and Eddington accretion ratio, L/L\rm Edd, over a wide range in redshift.
For low redshift QSOs, it has been demonstrated that M\rm BH can be derived from the velocity width of the broad H\beta emission line, and the distance of the emitting gas ~ luminosity0.6 (e.g., Kaspi et al. 2000). The evidence lies in the agreement between this M\rm BH and that derived from host galaxy masses (e.g., McLure & Dunlop 2002).
How can we measure M\rm BH and L/L\rm Edd at higher redshifts? We discuss several methods, using IR spectra of rest-frame H\beta at redshifts 1.5 -- 2.5 (Yuan, 2002), using widths of broad UV emission lines (redshifts up to 3.2, e.g., Vestergaard 2002, McLure & Jarvis 2002), using X-ray spectral index (to measure L/L\rm Edd), and using Principal Component Analyses of QSOs' UV emission line spectra. We demonstrate the use of the latter two methods, using the UV-optical spectra of the Laor (1994, 1997) PG sample (Shang 2002; see also the AAS dissertation talk to be given by Zhaohui Shang).
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.