Obscuration by Gas and Dust in Luminous Quasars

Abstract

We explore the connection between absorption by neutral gas and extinction by dust in mid-infrared (IR) selected luminous quasars. We use a sample of 33 quasars at redshifts 0.7 < z < 3 in the 9 deg^2 Boötes multiwavelength survey field that are selected using Spitzer Space Telescope Infrared Array Camera colors and are well-detected as luminous X-ray sources (with >150 counts) in Chandra observations. We divide the quasars into dust-obscured and unobscured samples based on their optical to mid-IR color, and measure the neutral hydrogen column density N_H through fitting of the X-ray spectra. We find that all subsets of quasars have consistent power law photon indices equal to 1.9 that are uncorrelated with N_H. We classify the quasars as gas-absorbed or gas-unabsorbed if N_H > 10^22 cm^-2 or N_H < 10^22 cm^-2, respectively. Of 24 dust-unobscured quasars in the sample, only one shows clear evidence for significant intrinsic N_H, while 22 have column densities consistent with N_H < 10^22 cm^-2. In contrast, of the nine dust-obscured quasars, six show evidence for intrinsic gas absorption, and three are consistent with N_H < 10^22 cm^-2. We conclude that dust extinction in IR-selected quasars is strongly correlated with significant gas absorption as determined through X-ray spectral fitting. These results suggest that obscuring gas and dust in quasars are generally co-spatial, and confirm the reliability of simple mid-IR and optical photometric techniques for separating quasars based on obscuration.

arXiv comment5 pages, 3 figures

References in corpus (36)

• A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: I. Galaxy Mergers & Quasar Activity
• Cosmological Evolution of the Hard X-ray AGN Luminosity Function and the Origin of the Hard X-ray Background
• Mid-Infrared Selection of Active Galaxies
• Obscured and unobscured active galactic nuclei in the Spitzer Space Telescope First Look Survey
• Toward the Standard Population Synthesis Model of the X-Ray Background: Evolution of X-Ray Luminosity and Absorption Functions of Active Galactic Nuclei Including Compton-Thick Populations
• Luminosity-dependent evolution of soft X-ray selected AGN: New Chandra and XMM-Newton surveys
• The Chandra Deep Field-South Survey: 4 Ms Source Catalogs
• X-ray spectral properties of AGN in the Chandra Deep Field South
• Candidate Type II Quasars from the Sloan Digital Sky Survey: I. Selection and Optical Properties of a Sample at 0.3<Z<0.83
• The incidence of obscuration in active galactic nuclei
• Space density of optically-selected type 2 quasars
• Infrared power-law galaxies in the Chandra Deep Field South: AGN and ULIRGs
• The Massive Hosts of Radio Galaxies Across Cosmic Time
• Spitzer's Contribution to the AGN Population
• Chandra and Spitzer unveil heavily obscured quasars in the SWIRE/Chandra Survey
• The IRAC Shallow Survey
• The Chandra Deep Field North Survey. VI. The Nature of the Optically Faint X-ray Source Population
• AGES: The AGN and Galaxy Evolution Survey
• Obscured AGN and the X-ray, Optical and Far-Infrared Number Counts of AGN in the GOODS Fields
• XBootes: An X-Ray Survey of the NDWFS Bootes Field - Paper I Overview and Initial Results
• Photometric Redshifts in the IRAC Shallow Survey
• Chandra Detection of a TypeII Quasar at z=3.288
• A Characteristic Division Between the Fueling of Quasars and Seyferts: Five Simple Tests
• Reliable Identification of Compton-thick Quasars at z~2: Spitzer Mid-IR spectroscopy of HDF-oMD49
• Candidate Type II Quasars from the SDSS: III. Spectropolarimetry Reveals Hidden Type I Nuclei
• A large population of mid-infrared selected, obscured active galaxies in the Bootes field
• The evolutionary sequence of active galactic nuclei and galaxy formation revealed
• Spectral energy distributions and luminosities of galaxies and AGN in the SPITZER SWIRE Legacy Survey
• Clustering of obscured and unobscured quasars in the Bootes field: Placing rapidly growing black holes in the cosmic web
• Candidate Type II Quasars from the Sloan Digital Sky Survey: II. From Radio to X-Rays
• A population of high-redshift type-2 quasars-I. Selection Criteria and Optical Spectra
• The Chandra-COSMOS survey IV: X-ray spectra of the bright sample
• Does the AGN Unified Model Evolve with Redshift? Utilizing the X-ray Background to Predict the Mid-Infrared Emission of AGN
• The quest for Type 2 quasars: Chandra observations of luminous obscured quasars in the Sloan Digital Sky Survey
• The HELLAS2XMM Survey. XII. The infrared/sub-millimeter view of an X-ray selected Type 2 quasar at z=2
• The OPTX Project III: X-ray versus Optical Spectral Type for AGNs

Cited by in corpus (3)

• A Connection between Obscuration and Star Formation in Luminous Quasars
• The Dust-to-Gas Ratio and the Role of Radiation Pressure in Luminous, Obscured Quasars
• Physical Models for the Clustering of Obscured and Unobscured Quasars