科研之友
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摘要
We present an analysis of broad emission lines observed in moderate-luminosity active galactic nuclei (AGNs), typical of those found in X-ray surveys of deep fields, with the goal of testing the validity of single-epoch virial black hole mass estimates. We have acquired near-infrared spectra of AGNs up to z similar to 1.8 in the COSMOS and Extended Chandra Deep Field-South Survey, with the Fiber Multi-Object Spectrograph mounted on the Subaru telescope. These near-infrared spectra provide a significant detection of the broad H alpha line, shown to be a reliable probe of black hole mass at low redshift. Our sample has existing optical spectroscopy that provides a detection of Mg II, typically used for black hole mass estimation at z greater than or similar to 1. We carry out a spectral-line fitting procedure using both H alpha and Mg II to determine the virial velocity of gas in the broad-line region, the continuum luminosity at 3000 angstrom, and the total H alpha line luminosity. With a sample of 43 AGNs spanning a range of two decades in luminosity, we find a tight correlation between the ultraviolet and emission-line luminosity. There is also a close one-to-one relationship between the full width at half-maximum of H alpha and Mg II. Both of these then lead to there being very good agreement between H alpha- and Mg II-based masses over a wide range in black hole mass, i.e., M-BH similar to 10(7-9) M-circle dot. In general, these results demonstrate that local scaling relations, using Mg II or H alpha, are applicable for AGNs at moderate luminosities and up to z similar to 2.
- 出版日期2013-7-1
