Infrared classification and luminosities for dusty active galactic nuclei and the most luminous quasars

Abstract

Mid-infrared spectroscopic measurements from the Infrared Spectrometer (IRS) on Spitzer are given for 125 hard X-ray active galactic nuclei (AGNs; 14-195 keV) from the Swift Burst Alert Telescope (BAT) sample and for 32 AGNs with black hole masses (BHMs) from reverberation mapping. The 9.7 μm silicate feature in emission or absorption defines an infrared AGN classification describing whether AGNs are observed through dust clouds, indicating that 55% of the BAT AGNs are observed through dust. The mid-infrared dust continuum luminosity is shown to be an excellent indicator of intrinsic AGN luminosity, scaling closely with the hard X-ray luminosity, log νL ν(7.8 μm)/L(X) = -0.31 ± 0.35, and independent of classification determined from silicate emission or absorption. Dust luminosity scales closely with BHM, log νL ν(7.8 μm) = (37.2 ± 0.5) + 0.87 log BHM for luminosity in erg s-1 and BHM in M⊙. The 100 most luminous type 1 quasars as measured in νL ν(7.8 μm) are found by comparing Sloan Digital Sky Survey (SDSS) optically discovered quasars with photometry at 22 μm from the Wide-Field Infrared Survey Explorer (WISE), scaled to rest frame 7.8 μm using an empirical template determined from IRS spectra. The most luminous SDSS/WISE quasars have the same maximum infrared luminosities for all 1.5 < z < 5, reaching total infrared luminosity L IR= 1014.4 L. Comparing with dust-obscured galaxies from Spitzer and WISE surveys, we find no evidence of hyperluminous obscured quasars whose maximum infrared luminosities exceed the maximum infrared luminosities of optically discovered quasars. Bolometric luminosities L bolestimated from rest-frame optical or ultraviolet luminosities are compared to L IR. For the local AGN, the median log LIR/L bol= -0.35, consistent with a covering factor of 45% for the absorbing dust clouds. For the SDSS/WISE quasars, the median log LIR/L bol= 0.1, with extremes indicating that ultraviolet-derived L bolcan be seriously underestimated even for type 1 quasars. © 2012. The American Astronomical Society. All rights reserved..