On the fraction of X-ray obscured quasars in the local universe

Abstract

Recent wide area hard X-ray and soft Gamma ray surveys have shown that the fraction of X-ray obscured AGNs in the local universe significantly decreases with intrinsic luminosity. In this letter we point out that two correction have to be made to the samples: 1) radio loud AGNs have to be excluded since their X-ray emission might be dominated by the jet component; 2) Compton thick sources have to be excluded too since their hard X-ray and soft gamma ray emission are also strongly attenuated by Compton scattering. The soft gamma-ray selected AGN samples obtained by SWIFT and INTEGRAL provide the best opportunity to study the fraction of obscured AGN in the local universe in the least biased way. We choose these samples to check if the corrections could alter the above result on the fraction of obscured AGNs. We find that before the corrections both samples show significant anti-correlation between L_X and N_H, indicating obvious decrease in the fraction of obscured AGNs with luminosity. However, after the corrections, we find only marginal evidence of anti-correlation (at 98% confidence level) in the SWIFT sample, and no evidence at all in the INTEGRAL sample which consists of comparable number of objects. We conclude that current samples only show a marginal decrease in the fraction of obscured AGNs in the local universe, and much larger samples are required to reach a more robust conclusion.

arXiv comment13 pages, including 4 figures, ApJ letter accepted

References in corpus (38)

• Cosmological Evolution of the Hard X-ray AGN Luminosity Function and the Origin of the Hard X-ray Background
• The Cosmic Evolution of Hard X-ray Selected Active Galactic Nuclei
• The HELLAS2XMM survey. VII. The hard X-ray luminosity function of AGN up to z=4: more absorbed AGN at low luminosities and high redshifts
• Extreme X-ray spectral variability in the Seyfert 2 Galaxy NGC 1365
• The HELLAS2XMM survey: IV. Optical identifications and the evolution of the accretion luminosity in the Universe
• A Classic Type 2 QSO
• XMM-Newton observation of the Lockman Hole II. Spectral analysis
• The obscuration by dust of most of the growth of supermassive black holes
• The Changing AGN Population
• Chandra Detection of a TypeII Quasar at z=3.288
• The Swift/BAT High Latitude Survey: First Results
• The HELLAS2XMM survey: VI. X-ray absorption in the 1dfAGN sample through a spectral analysis
• The First INTEGRAL AGN Catalog
• The XMM-Newton HBS28 sample: studying the obscuration in hard X-ray selected AGNs
• The XMM-Newton view of Mrk3 and IXO30
• An XMM-Newton observation of Ark 120: the X-ray spectrum of a `bare' Seyfert 1 nucleus
• INTEGRAL/IBIS Extragalactic survey: 20-100 keV selected AGN
• The Serendipitous Extragalactic X-Ray Source Identification (SEXSI) Program. III. Optical Spectroscopy
• On the X-ray Baldwin effect for narrow Fe Kalpha emission line
• The recent X-ray history of NGC 5506
• XMM-Newton observations of a sample of gamma-ray loud active galactic nuclei
• XMM-Newton observations of the heavily absorbed Seyfert 1 galaxy IC 4329A
• Spectral Statistics and Local Luminosity Function of a Hard X-ray Complete Sample of Brightest AGNs
• INTEGRAL and XMM-Newton Spectral Studies of NGC 4388
• BeppoSAX Observation of NGC 7582: Constraints on the X-ray absorber
• The complex X-ray spectrum of NGC 4507
• Are There Any Type 2 QSOs? The Case of AXJ0341.4-4453
• The XMM-Newton View of the Broad-Line Radio Galaxy 3C 120
• XMM-Newton observations of Broad FeKalpha emission from a Seyfert 1.9 galaxy MCG-5-23-16
• A Simultaneous RXTE and XMM-Newton Observation of the Broad-Line Radio Galaxy 3C 111
• The High Energy Spectrum of NGC 4151
• An XMM-Newton Observation of the Seyfert 2 Galaxy NGC 6300. I. The Nucleus
• Chandra LETGS and XMM-Newton observations of NGC 4593
• Chandra High-Resolution X-ray Spectroscopy of the Fe K Line in the Seyfert 1 Galaxy NGC 3783
• XMM-Newton observation of the bright Seyfert 1 galaxy, MCG+8-11-11
• Extranuclear X-ray Emission in the Edge-on Seyfert Galaxy NGC 2992
• Monitoring RXTE Observations of Markarian 348: the origin of the column density variations
• Chandra-LETGS observation of Mrk 279: modeling the AGN internal structure

Cited by in corpus (9)

• An Observational Determination of the Bolometric Quasar Luminosity Function
• Active Galactic Nuclei: what's in a name?
• Half of the Most Luminous Quasars May Be Obscured: Investigating the Nature of WISE-Selected Hot, Dust-Obscured Galaxies
• Constraints on light bending and reflection from the hard X-ray background
• H alpha Star Formation Rates in Massive Galaxies at z ~ 1
• The Effect of Partial Obscuration on the Luminosity Dependence of the Obscured Fraction in Active Galactic Nuclei
• Type 1 Active Galactic Nucleus Fraction in SDSS/FIRST Survey
• Most hard X-ray selected quasars in Chandra Deep Fields are obscured
• Rapidly spinning massive black holes in active galactic nuclei: evidence from the black hole mass function