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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Matsuoka, K., Silverman, J.D., Schramm, M., Steinhardt, C.L., Nagao, T., Kartaltepe, J., Sanders, D.B., Treister, E., Hasinger, G., Akiyama, M., Ohta, K., Ueda, Y., Bongiorno, A., Brandt, W.N., Brusa, M., Capak, P., Civano, F., Comastri, A., Elvis, M., Lilly, S.J., Mainieri, V., Masters, D., Mignoli, M., Salvato, M., Trump, J.R., Taniguchi, Y., Zamorani, G., Alexander, D.M. & Schawinski, K. (2013). A comparative analysis of virial black hole mass estimates of moderate-luminosity active galactic nuclei using Subaru/FMOS. The astrophysical journal 771(1): 64.

Author(s) from Durham


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 ~ 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 Hα 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 >~ 1. We carry out a spectral-line fitting procedure using both Hα and Mg II to determine the virial velocity of gas in the broad-line region, the continuum luminosity at 3000 Å, and the total Hα 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 Hα and Mg II. Both of these then lead to there being very good agreement between Hα- and Mg II-based masses over a wide range in black hole mass, i.e., M BH ~ 107-9 M ⊙. In general, these results demonstrate that local scaling relations, using Mg II or Hα, are applicable for AGNs at moderate luminosities and up to z ~ 2.