A Spectroscopic Analysis of Broad-Line Active Galactic Nuclei (AGN) in the COMOS Field
Professor Adi Foord, Department of Physics
Morgan Robbins, Department of Computer Science and Electrical Engineering
Active Galactic Nuclei (AGNs) are extremely luminous objects powered by an accretion disk of gas that trigger growth periods in a supermassive black hole (SMBH) at the center of a galaxy. AGN BH mass estimates are used to track AGN evolution and calculate key values such as Eddington ratios (i.e., the rate of accretion in proportion to a theoretical maximum). AGN activity peaks at redshifts 1 < z < 3, so there is a need for precise BH mass estimates within this redshift range. We calculated single-epoch virial black hole mass estimates for over 150 broad-line AGN (FWHM >= 1200 km/s) at redshifts z < ~ 3 with the majority of the sample falling within the 1 < z < 3 range of peak AGN activity. Our targets were spectroscopically observed in shared-risk mode by the Subaru Prime Focus Spectrograph (PFS) and were previously X-ray selected (L0.5–10 keV > 1043 erg s-1) by the Chandra COSMOS survey. Using PyQSOFit, we modeled the broad components of the Mg II and H-beta line emission complexes with 1-2 Gaussians and the narrow components with 1 Gaussian while constraining flux of the forbidden [O III] λλ 4960, 5008 doublet to a 3:1 ratio. We then measured the FWHM of the Mg II and H-beta line emission complexes and continuum luminosity values (3000 Å, 5100 Å) needed to compute bolometric luminosities. Black hole mass estimates were calculated using the corresponding Wang et al. (2009) mass scaling relations. Preliminary results suggest that the sample has mean log(M_BH/M☉) ~ 8.6 and exists within a relatively narrow band of Eddington ratios 0.01 – 0.1. These measurements extend precise BH mass estimates to the epoch of peak AGN activity and will support studies of AGN growth and evolution.