The quest for Type 2 quasars: Chandra observations of luminous obscured quasars in the Sloan Digital Sky Survey

Abstract

We report on new Chandra exploratory observations of six candidate Type 2 quasars at z=0.49-0.73 selected among the most [OIII] luminous emitters from the Sloan Digital Sky Survey (SDSS). Under the assumption that [OIII] is a proxy for the intrinsic luminosity of the central source, their predicted rest-frame X-ray luminosities are L(2-10keV)~10^45 erg/s. For two of the targets, the photon statistics are good enough to allow for basic X-ray spectral analyses, which indicate the presence of intrinsic absorption (~10^{22-23} cm^-2) and luminous X-ray emission (L_X>10^44 erg/s). Of the remaining four targets, two are detected with only a few (3-6) X-ray counts, and two are undetected by Chandra. If these four sources have the large intrinsic X-ray luminosities predicted by the [OIII] emission, then their nuclei must be heavily obscured (N_H>few 10^23 cm^-2) and some might be Compton thick (N_H>1.5 10^24 cm^-2). We also present the results for two Type 2 quasar candidates serendipitously lying in the fields of the Chandra targets, and provide an up-to-date compilation of the X-ray properties of eight additional SDSS Type 2 quasars from archival Chandra and XMM-Newton observations (five with moderate-quality X-ray data). The combined sample of 16 SDSS Type 2 quasars (10 X-ray detections) provides further evidence that a considerable fraction of optically selected Type 2 quasars are obscured in the X-ray band (at least all the objects with moderate-quality X-ray spectra), lending further support to the findings presented in Vignali, Alexander and Comastri (2004a) and unification schemes of Active Galactic Nuclei, and confirms the reliability of [OIII] emission in predicting the X-ray emission in obscured quasars.

9 pages, 6 figures, 5 tables, accepted by MNRAS

References in corpus (44)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Determination of Cosmological Parameters
• The Sloan Digital Sky Survey: Technical Summary
• The First Data Release of the Sloan Digital Sky Survey
• The Chandra Deep Field-North Survey. XIII. 2 Ms Point-Source Catalogs
• The Chandra Deep Field South: the 1 Million Second
• The Chandra Deep Field South: Optical Spectroscopy I
• A Wavelet-Based Algorithm for the Spatial Analysis of Poisson Data
• The XMM-Newton view of PG quasars I. X-ray continuum and absorption
• Deep Extragalactic X-ray Surveys
• A 3 dimensional diagnostic diagram for Seyfert 2s: probing X-ray absorption and Compton thickness
• 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 Spectra of a large sample of Quasars with ASCA
• Candidate Type II Quasars from the Sloan Digital Sky Survey: I. Selection and Optical Properties of a Sample at 0.3<Z<0.83
• Absolute measurement of the unresolved cosmic X-ray background in the 0.5-8 keV band with Chandra
• On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies
• Optical and Infrared Properties of the 2 Ms Chandra Deep Field-North X-ray Sources
• The Fall of AGN and the Rise of Star-Forming Galaxies: A Close Look at the Chandra Deep Field X-ray Number Counts
• 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
• Testing current synthesis models of the X-ray background
• The Chandra Deep Field North Survey. VI. The Nature of the Optically Faint X-ray Source Population
• Chandra Detection of a TypeII Quasar at z=3.288
• XMM-Newton spectroscopy of high-redshift QSOs
• Type II Quasars from the Sloan Digital Sky Survey: V. Imaging host galaxies with the Hubble Space Telescope
• Candidate Type II Quasars from the SDSS: III. Spectropolarimetry Reveals Hidden Type I Nuclei
• Chandra Observations of the Highest Redshift Quasars from the Sloan Digital Sky Survey
• Candidate Type II Quasars from the Sloan Digital Sky Survey: II. From Radio to X-Rays
• The Correlation of Narrow Line Emission and X-ray Luminosity in Active Galactic Nuclei
• The HELLAS2XMM survey: VI. X-ray absorption in the 1dfAGN sample through a spectral analysis
• X-ray Lighthouses of the High-Redshift Universe. II. Further Snapshot Observations of the Most Luminous z>4 Quasars with Chandra
• The XMM-Newton HBS28 sample: studying the obscuration in hard X-ray selected AGNs
• The BeppoSAX High Energy Large Area Survey HELLAS, III: testing synthesis models for the X-ray background
• The X-ray Spectral Properties and Variability of Luminous High-Redshift Active Galactic Nuclei
• The HELLAS2XMM survey. V. Near-Infrared observations of X-ray sources with extreme X/O ratios
• Powerful obscured AGN among X-ray hard, optically-dim serendipitous Chandra sources
• The Chandra Deep Field South/GOODS survey. Optically faint X-ray sources
• Chandra and XMM Observations of Type II Quasars from the SDSS
• Sub-mm detection of a high redshift Type 2 QSO
• Compton-Thick X-ray Absorption in the Seyfert Galaxies Tololo 0109-383 and ESO 138-G1
• Multi-wavelength observations of serendipitous Chandra X-ray sources in the field of A2390
• Infrared observations of serendipitous hard Chandra X-ray sources
• The HELLAS2XMM survey. IX. Spectroscopic identification of super-EROs hosting AGNs
• Evidence for X-ray Obscuration in Type II Quasar Candidates from the Sloan Digital Sky Survey

Cited by in corpus (35)

• Space density of optically-selected type 2 quasars
• The KMOS AGN Survey at High redshift (KASHz): the prevalence and drivers of ionised outflows in the host galaxies of X-ray AGN
• Clustering of obscured and unobscured quasars in the Bootes field: Placing rapidly growing black holes in the cosmic web
• The X-ray to [Ne V]3426 flux ratio: discovering heavily obscured AGN in the distant Universe
• NuSTAR unveils a Compton-thick Type 2 quasar in Mrk 34
• NuSTAR Reveals Extreme Absorption in z < 0.5 Type 2 Quasars
• NuSTAR Observations of Heavily Obscured Quasars at z ~ 0.5
• Mid-infrared spectra of optically selected type 2 quasars
• A Comparison of X-ray and Mid-Infrared Selection of Obscured AGN
• XMM-Newton Observations of a Complete Sample of Optically Selected Type 2 Seyfert Galaxies
• Cross-correlation of the 2XMMi catalogue with Data Release 7 of the Sloan Digital Sky Survey
• A wide search for obscured Active Galactic Nuclei using XMM-Newton and WISE
• The Chandra Deep Fields: Lifting the Veil on Distant Active Galactic Nuclei and X-Ray Emitting Galaxies
• The NuSTAR Serendipitous Survey: Hunting for The Most Extreme Obscured AGN at >10 keV
• The Radio Properties of Type 2 Quasars
• Composite Spectral Energy Distributions and Infrared-Optical Colors of Type 1 and Type 2 Quasars
• Dusty torus formation by anisotropic radiative pressure feedback of active galactic nuclei
• An Archival Chandra and XMM-Newton Survey of Type 2 Quasars
• The space density of Compton-thick AGN at z~0.8 in the zCOSMOS-Bright Survey
• Defocussed Transmission Spectroscopy: A potential detection of sodium in the atmosphere of WASP-12b
• A Search for Optical Variability of Type 2 Quasars in SDSS Stripe 82
• Heavy absorption and soft X-ray emission lines in the XMM-Newton spectrum of the Type 2 radio-loud quasar 3C 234
• Discovery of Compton-thick quasars in the Sloan Digital Sky Survey
• X-ray and multi-epoch optical/UV investigations of BAL to non-BAL quasar transformations
• XMM-Newton reveals a Seyfert-like X-ray spectrum in the z=3.6 QSO B1422+231
• COSMOS2020: Investigating the AGN-obscured accretion phase at $z\sim 1$ via [NeV] selection
• XMM-Newton and NuSTAR Observations of an Optically Quiescent Quasar
• A population of Optically Quiescent Quasars from WISE and SDSS
• On the nature of red galaxies: the Chandra perspective
• The Complex X-ray Obscuration Environment in the Radio Loud Type 2 Quasar 3C 223
• Properties of IR selected Active Galactic Nuclei
• LBT-MODS spectroscopy of high-redshift candidates in the Chandra J1030 field. A newly discovered z$\sim$2.8 large scale structure
• Obscuration by Gas and Dust in Luminous Quasars
• Obscured accretion from AGN surveys
• X-ray selection of Compton Thick AGN at high redshift