The Serendipitous Extragalactic X-Ray Source Identification (SEXSI) Program. III. Optical Spectroscopy

Abstract

We present the catalog of 477 spectra from the Serendipitous Extragalactic X-ray Source Identification (SEXSI) program, a survey designed to probe the dominant contributors to the 2-10 keV cosmic X-ray background. Our survey covers 1 deg^2 of sky to 2-10 keV fluxes of 10^-14 erg cm^-2 s^-1, and 2 deg^2 for fluxes of 3 x 10^-14 erg cm^-2 s^-1. Our spectra reach to R <24 and have produced redshifts for 438 hard X-ray sources. The vast majority of the 2-10 keV-selected sample are AGN with redshifts between 0.1 and 3. We find that few sources at z<1 have high X-ray luminosities, reflecting a dearth of high-mass, high-accretion-rate sources at low redshift, a result consistent with other recent wide-area surveys. Half of our sources show significant obscuration, with N_H>10^22 cm^-2, independent of unobscured luminosity. We classify 168 sources as emission-line galaxies; all are X-ray luminous objects with optical spectra lacking both high-ionization lines and evidence of a non-stellar continuum. The redshift distribution of these emission-line galaxies peaks at a significantly lower redshift than does that of the sources we spectroscopically identify as AGN. We conclude that few of these sources can be powered by starburst activity. Stacking spectra for a subset of these sources, we detect [Ne V] emission, a clear signature of AGN activity, confirming that the majority of these objects are Seyfert 2s in which the high-ionization lines are diluted by stellar emission. We find 33 objects lacking broad lines in their optical spectra which have quasar X-ray luminosities (Lx>10^44 erg s^-1), the largest sample of such objects identified to date. In addition, we explore 17 AGN associated with galaxy clusters and find that the cluster-member AGN sample has a lower fraction of broad-line AGN than does the background sample.

Accepted to ApJ; 57 pages, 25 figures, 5 tables

References in corpus (50)

• Composite Quasar Spectra From the Sloan Digital Sky Survey
• The Chandra Deep Field-North Survey. XIII. 2 Ms Point-Source Catalogs
• High Mass X-ray Binaries as a Star Formation Rate Indicator in Distant Galaxies
• The Chandra Deep Field South: Optical Spectroscopy I
• The 2-10 keV luminosity as a Star Formation Rate indicator
• A Survey of Star-Forming Galaxies in the z=1.4-2.5 `Redshift Desert': Overview
• Deep Extragalactic X-ray Surveys
• 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 Chandra Deep Survey of the Hubble Deep Field North Area. II. Results from the Caltech Faint Field Galaxy Redshift Survey Area
• The HELLAS2XMM survey: IV. Optical identifications and the evolution of the accretion luminosity in the Universe
• A Classic Type 2 QSO
• The evolution of faint AGN between z~1 and z~5 from the COMBO-17 survey
• X-ray Spectroscopy of QSOs with Broad Ultraviolet Absorption Lines
• "Hidden" Seyfert 2 Galaxies and the X-ray Background
• X-Rays from NGC 3256: High-Energy Emission in Starburst Galaxies and Their Contribution to the Cosmic X-Ray Background
• Lx-SFR relation in star forming galaxies
• The HELLAS2XMM survey: II. Multiwavelength observations of P3: an X-ray bright, optically inactive galaxy
• Obscured AGN and the X-ray, Optical and Far-Infrared Number Counts of AGN in the GOODS Fields
• Chandra Detection of a TypeII Quasar at z=3.288
• The RGB Sample of Intermediate BL Lacs
• The Nature of X-ray Bright Optically Normal Galaxies
• Optical Identification of the ASCA Large Sky Survey
• The HELLAS2XMM survey: I. The X-ray data and the Log(N)-Log(S)
• Chandra Multi-wavelength Project (ChaMP). I. First X-ray Source Catalog
• Supermassive Black Hole Accretion History Inferred from a Large Sample of Chandra Hard X-ray Sources
• The HELLAS2XMM survey: VI. X-ray absorption in the 1dfAGN sample through a spectral analysis
• 2-8 keV X-ray number counts determined from Chandra blank field observations
• FIRST-2MASS Sources Below the APM Detection Threshold: A Population of Highly Reddened Quasars
• Hard X-ray emitting Active Galactic Nuclei selected by the Chandra Multi-wavelength Project
• The Sedentary Multi-Frequency Survey. I. Statistical Identification and Cosmological Properties of HBL BL Lacs
• The Chandra Multiwavelength Project: Optical Followup of Serendipitous Chandra Sources
• Optical Identification of the ASCA Medium Sensitivity Survey in the Northern Sky: Nature of Hard X-ray-selected Luminous Active Galactic Nuclei
• A Galaxy at z = 6.545 and Constraints on the Epoch of Reionization
• An Unexpectedly High AGN Fraction in Red Cluster Galaxies
• The Hellas2XMM survey: III. Multiwavelength observations of hard X-ray selected sources in the PKS 0312-77 field
• The BeppoSAX High Energy Large Area Survey -V. The nature of the hard X-ray source populations and its evolution
• The Serendipitous Extragalactic X-Ray Source Identification (SEXSI) Program: I. Characteristics of the Hard X-Ray Sample
• SPICES II. Optical and Near-Infrared Identifications of Faint X-Ray Sources from Deep Chandra Observations of Lynx
• The Chandra Large Area Synoptic X-ray Survey (CLASXS) of the Lockman Hole-Northwest: The X-ray Catalog
• Moderate Temperature Clusters of Galaxies from the RDCS and the High Redshift Luminosity-Temperature Relation
• An Optical Catalog of the Chandra Large Area Synoptic X-ray Survey Sources
• The Chandra Deep Field-North Survey: XVII. Evolution of magnetic activity in old late-type stars
• The Hard X-ray Luminosity of OB Star Populations: Implications for the Contribution of Star Formation to the Cosmic X-ray Background
• Are There Any Type 2 QSOs? The Case of AXJ0341.4-4453
• Optical and Near-Infrared Spectroscopy of a High-Redshift, Hard X-ray Emitting Spiral Galaxy
• The Calan-Yale Deep Extragalactic Research (CYDER) Survey: Optical Properties and Deep Spectroscopy of Serendipitous X-ray Sources
• Spectroscopic Confirmation of a Radio-Selected Galaxy Overdensity at z=1.11
• Obscured AGN: the hidden side of the X-ray Universe
• The Serendipitous Extragalactic X-Ray Source Identification (SEXSI) Program: II. Optical Imaging

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• Spectral Energy Distributions of Hard X-ray selected AGNs in the XMDS Survey
• AGN Dusty Tori: II. Observational Implications of Clumpiness
• 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
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• The Evolution of Active Galactic Nuclei in Clusters of Galaxies to Redshift 1.3
• XMM-Newton observations of the Lockman Hole: X-ray source catalogue and number counts
• The Cosmic Evolution of AGN in galaxy clusters
• First Measurement of a Rapid Increase in the AGN Fraction in High-Redshift Clusters of Galaxies
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• Wide-field mid-infrared and millimetre imaging of the high-redshift radio galaxy, 4C41.17
• A new infrared color criterion for the selection of 0<z<7 AGN: application to deep fields and implications for JWST surveys
• The HELLAS2XMM survey.VIII. Optical identifications of the extended sample
• Constraints on the Accretion History of Massive Black Holes from Faint X-ray Counts
• Determining the torus covering factors for a sample of type 1 AGN in the local Universe
• Does the AGN Unified Model Evolve with Redshift? Utilizing the X-ray Background to Predict the Mid-Infrared Emission of AGN
• The XMM large scale structure survey: optical vs. X-ray classifications of active galactic nuclei and the unified scheme
• Obscured and unobscured AGN populations in a hard-X-ray selected sample of the XMDS survey
• Morphologies of Radio, X-Ray, and Mid-Infrared Selected AGN
• The X-ray luminosity function of AGN at z~3
• The XMM-Newton survey of the ELAIS-S1 field II: optical identifications and multiwavelength catalogue of X-ray sources
• Heavy absorption and soft X-ray emission lines in the XMM-Newton spectrum of the Type 2 radio-loud quasar 3C 234
• Outflow vs. Infall in Spiral Galaxies: Metal Absorption in the Halo of NGC 891
• Active galactic nuclei ghosts: A systematic search for faded nuclei
• The Effect of Partial Obscuration on the Luminosity Dependence of the Obscured Fraction in Active Galactic Nuclei
• Early Science Result from the Japanese Virtual Observatory: AGN and Galaxy Clustering at z = 0.3 to 3.0
• The dependency of AGN infrared color-selection on source luminosity and obscuration: An observational perspective in CDFS and COSMOS
• On the fraction of X-ray obscured quasars in the local universe
• X-ray Absorption and Optical Extinction in the Partially Obscured Seyfert Nucleus in Mrk 1393
• The eROSITA Final Equatorial Depth Survey (eFEDS): the hard X-ray selected sample
• Most hard X-ray selected quasars in Chandra Deep Fields are obscured
• Is J 133658.3-295105 a Radio Source at z >= 1.0 or at the Distance of M 83?
• The Evolution of Radio Galaxies and X-ray Point Sources in Coma Cluster Progenitors Since z~1.2
• On the nature of high X-ray luminosities in SDSS galaxies
• Chandra Survey in the AKARI North Ecliptic Pole Deep Field Optical/Infrared Identifications of X-ray Sources