Discovery of optically faint obscured quasars with Virtual Observatory tools

Abstract

We use Virtual Observatory (VO) tools to identify optically faint, obscured (i.e., type 2) active galactic nuclei (AGN) in the two Great Observatories Origins Deep Survey (GOODS) fields. By employing publicly available X-ray and optical data and catalogues we discover 68 type 2 AGN candidates. The X-ray powers of these sources are estimated by using a previously known correlation between X-ray luminosity and X-ray-to-optical flux ratio. Thirty-one of our candidates have high estimated powers (Lx > 10^44 erg/s) and therefore qualify as optically obscured quasars, the so-called ``QSO 2''. Based on the derived X-ray powers, our candidates are likely to be at relatively high redshifts, z ~ 3, with the QSO 2 at z ~ 4. By going ~ 3 magnitudes fainter than previously known type 2 AGN in the two GOODS fields we are sampling a region of redshift - power space which was previously unreachable with classical methods. Our method brings to 40 the number of QSO 2 in the GOODS fields, an improvement of a factor ~ 4 when compared to the only 9 such sources previously known. We derive a QSO 2 surface density down to 10^-15 erg/cm^2/s in the 0.5 - 8 keV band of >~ 330/deg^2, ~ 30% of which is made up of previously known sources. This is larger than current estimates and some predictions and suggests that the surface density of QSO 2 at faint flux limits has been underestimated. This work demonstrates that VO tools are mature enough to produce cutting-edge science results by exploiting astronomical data beyond ``classical'' identification limits (R <~ 25) with interoperable tools for statistical identification of sources using multiwavelength information.

arXiv comment16 pages, 6 figures, accepted for publication in Astronomy & Astrophysics. PDF file with higher resolution figures available at http://www.eso.org/~ppadovan/AVO-paper.pdf

References in corpus (21)

• Unified Schemes for Radio-Loud Active Galactic Nuclei
• The Great Observatories Origins Deep Survey: Initial Results From Optical and Near-Infrared Imaging
• The VizieR database of Astronomical Catalogues
• Bayesian photometric redshift estimation
• The Chandra Deep Field-North Survey. XIII. 2 Ms Point-Source Catalogs
• The Chandra Deep Field South: the 1 Million Second
• ANNz: estimating photometric redshifts using artificial neural networks
• Optical and Infrared Properties of the 2 Ms Chandra Deep Field-North X-ray Sources
• The Team Keck Treasury Redshift Survey of the GOODS-North Field
• The HELLAS2XMM survey: IV. Optical identifications and the evolution of the accretion luminosity in the Universe
• A Classic Type 2 QSO
• Testing current synthesis models of the X-ray background
• "Hidden" Seyfert 2 Galaxies and the X-ray Background
• Photometric Redshifts for Galaxies in the GOODS Southern Field
• The HELLAS2XMM survey: VI. X-ray absorption in the 1dfAGN sample through a spectral analysis
• A multivariate statistical analysis of spiral galaxy luminosities. I. Data and results
• The BeppoSAX High Energy Large Area Survey HELLAS, III: testing synthesis models for the X-ray background
• The Space Density of High-Redshift QSOs in the GOODS Survey
• Powerful obscured AGN among X-ray hard, optically-dim serendipitous Chandra sources
• Photometric redshifts in the Hubble Deep Fields: evolution of extinction and the star-formation rate
• Star Formation and X-ray Emission in Distant Star Forming Galaxies

Cited by in corpus (22)

• Passively Evolving Early-type Galaxies at 1.4<z<2.5 in the Hubble Ultra Deep Field
• VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open cluster
• 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
• X-ray spectral properties of AGN in the Chandra Deep Field South
• The Fall of AGN and the Rise of Star-Forming Galaxies: A Close Look at the Chandra Deep Field X-ray Number Counts
• A mean redshift of 2.8 for Swift gamma-ray bursts
• Chandra and Spitzer unveil heavily obscured quasars in the SWIRE/Chandra Survey
• X-ray Emission from Optically Selected Radio-Intermediate and Radio-Loud Quasars
• XMM-Newton observations of Extremely Red Objects and the link with luminous, X-ray obscured Quasars
• The XMM Large Scale Structure Survey: Properties and Two-Point Angular Correlations of Point-like Sources
• Young stars and brown dwarfs surrounding Alnilam (eps Ori) and Mintaka (del Ori)
• X-ray spectral analysis of optically faint sources in the Chandra Deep Fields
• Chandra and Spitzer observations of CDFS X-ray obscured QSOs
• A z=3.045 Lyman alpha emitting halo hosting a QSO and a possible candidate for AGN-triggered star-formation
• Using VO tools to investigate distant radio starbursts hosting obscured AGN in the HDF(N) region
• The XMM-Newton spectrum of the high-z optically-obscured QSO RX J1343.4+0001: a classic radio quiet QSO
• Euro-VO - Coordination of Virtual Observatory activities in Europe
• VisIVOWeb: A WWW Environment for Large-Scale Astrophysical Visualization
• Quasars and their host galaxies
• Searching for gravitational waves emitted by binaries with spinning components
• High-energy Astrophysics and the Virtual Observatory