The XMM-Newton Wide-Field Survey in the COSMOS Field. III. Optical Identification and Multiwavelength Properties of a Large Sample of X-Ray-Selected Sources

By M. Brusa, G. Zamorani, A. Comastri, G. Hasinger, N. Cappelluti, F. Civano, A. Finoguenov, V. Mainieri, Mara Salvato, C. Vignali and 24 more. 2006

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We present the optical identification of a sample of 695 X-ray sources detected in the first 1.3 deg2 of the COSMOS XMM-Newton survey, down to a 0.5-2 keV (2-10 keV) limiting flux of ~10-15 erg cm-2 s-1 (~5 × 10-15 erg cm-2 s-1). In order to identify the correct optical counterparts and to assess the statistical significance of the X-ray-to-optical associations we have used the "likelihood ratio technique." Here we present the identification method and its application to the CFHT I-band and photometric catalogs. We were able to associate a candidate optical counterpart to ~90% (626) of the X-ray sources, while for the remaining ~10% of the sources we were not able to provide a unique optical association due to the faintness of the possible optical counterparts (IAB > 25) or to the presence of multiple optical sources, with similar likelihoods of being the correct identification, within the XMM-Newton error circles. We also cross-correlated the candidate optical counterparts with the Subaru multicolor and ACS catalogs and with the Magellan/IMACS, zCOSMOS, and literature spectroscopic data; the spectroscopic sample comprises 248 objects (~40% of the full sample). Our analysis of this statistically meaningful sample of X-ray sources reveals that for ~80% of the counterparts there is a very good agreement between the spectroscopic classification, the morphological parameters as derived from ACS data, and the optical-to-near-infrared colors: the large majority of spectroscopically identified broad-line active galactic nuclei (BL AGNs) have a pointlike morphology on ACS data, blue optical colors in color-color diagrams, and an X-ray-to-optical flux ratio typical of optically selected quasars. Conversely, sources classified as narrow line AGNs or normal galaxies are on average associated with extended optical sources, have significantly redder optical-to-near-infrared colors, and span a larger range of X-ray-to-optical flux ratios. However, about 20% of the sources show an apparent mismatch between the morphological and spectroscopic classifications. All the "extended" BL AGNs lie at redshift <1.5, while the redshift distribution of the full BL AGN population peaks at z ~ 1.5. The most likely explanation is that in these objects the nuclear emission is not dominant with respect to the host galaxy emission in the observed ACS band. Our analysis also suggests that the type 2/type 1 ratio decreases toward high luminosities, in qualitative agreement with the results from X-ray spectral analysis and the most recent modeling of the X-ray luminosity function evolution.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

AEGIS-X: THE CHANDRA DEEP SURVEY OF THE EXTENDED GROTH STRIP (2008, methodology): “We identify secure optical and IR counterparts to the Chandra X-ray sources using the maximum likelihood (LR) method (Ciliegi et al. 2003, 2005; Brusa et al. 2007).”
The DEIMOS 10K Spectroscopic Survey Catalog of the COSMOS Field (2018, background): “…Spitzer MIPS (Kartaltepe et al. 2010a, 2010b) and Herschel PACS sources (Lee et al. 2013), as well as X-ray sources discovered by XMM-Newton (e.g., Brusa et al. 2007, 2009, 2010; Elvis et al. 2012) and Chandra (e.g., Civano et al. 2012; Marchesi et al. 2016a, 2016b) and to determine the most…”
THE CHANDRA COSMOS SURVEY. I. OVERVIEW AND POINT SOURCE CATALOG (2009, background): “The Chandra sources have already resolved ambiguous source identifications from the XMM-COSMOS survey (Hasinger – 32 – et al. 2007, Brusa et al. 2007, 2008, Cappelluti et al. 2007, 2009).”
Photometric Redshifts of Galaxies in COSMOS (2006, background): “A total of 12 galaxies in the spectroscopic sample (z < 1:2) were identified as AGNs from their X-ray emission (Brusa et al. 2007).”
COSBO: The MAMBO 1.2 Millimeter Imaging Survey of the COSMOS Field (2007, background): “X-Ray Counterparts Wecross-correlated ourMAMBOsourceswith theX-ray source counterparts from the XMM-Newton observations (Hasinger et al. 2007; Brusa et al. 2007).”
The COSMOS2015 galaxy stellar mass function . Thirteen billion years of stellar mass assembly in ten snapshots (2017, background): “They increase the exponential tail of our SMF at least at z 6 3, while at higher redshift the number of sources detected by Chandra or XMM is too small (Fig.”
PHOTOMETRIC REDSHIFT AND CLASSIFICATION FOR THE XMM–COSMOS SOURCES (2008, methodology): “A detailed X–ray to optical association using COSMOS optical, near- and mid-infrared catalogs was performed using the Maximum Likelihood (ML) technique (Brusa et al. 2007, 2008).”
Dusty Star Forming Galaxies at High Redshift (2014, methodology): “This likelihood ratio (LR) method was developed in Sutherland and Saunders (1992) with additional improvements in Ciliegi et al. (2003), Brusa et al. (2007) and – in the context of submillimeter data – in Chapin et al. (2011).”
THE BULK OF THE BLACK HOLE GROWTH SINCE z ∼ 1 OCCURS IN A SECULAR UNIVERSE: NO MAJOR MERGER–AGN CONNECTION (2010, methodology): “We use the catalog presented in Brusa et al. (2010), which provides the most likely optical and infrared counterparts to the XMM sources based on a likelihood ratio technique (see Brusa et al. 2007 for details).”
Mass assembly in quiescent and star-forming galaxies since z ≃ 4 from UltraVISTA (2013, unknown): “We remove the stars and X-ray detected AGNs (Brusa et al. 2007).”
THE CHANDRA COSMOS LEGACY SURVEY: OPTICAL/IR IDENTIFICATIONS (2015, methodology): “This procedure was applied first to the XMM-COSMOS catalog (Brusa et al. 2007, hereafter B07; B10) with a percentage of “reliable identifications” greater than 80%, and later on C-COSMOS with a percentage of “reliable identifications” of ≃96%.”
ACTIVE GALACTIC NUCLEUS HOST GALAXY MORPHOLOGIES IN COSMOS (2009, background): “An object is identified as an AGN candidate through detection as an X-ray point source above the ∼10−15 erg cm−2 s−1 flux limit in the 0.5–2 keV or 2–10 keV flux bands (Cappelluti et al. 2007; Brusa et al. 2007), or a radio source above the 0.1 mJy flux limit at 1.4 GHz (Schinnerer et al. 2007).”
The XMM-Newton Wide-Field Survey in the COSMOS Field. I. Survey Description (2006, methodology): “The diagnostic line ratios log [OIII]/Hβ=0.61 and log [NII]/Hα=0.12 put this object among the bulk of the normal Seyfert–2 galaxies.”
CHASING HIGHLY OBSCURED QSOs IN THE COSMOS FIELD (2008, methodology): “Sources with a direct X-ray detection 232 sources of the COSMOS Bright MIPS sample are present in the C-COSMOS and XMM-COSMOS catalogs (Elvis et al. 2008, Civano et al. 2008, Brusa et al. 2007, 2008a).”
zCOSMOS: A Large VLT/VIMOS Redshift Survey Covering 0 < z < 3 in the COSMOS Field (2006, background): “X-Ray, Radio, and Ultraviolet Selected Targets Target lists of X-ray (Hasinger et al. 2007; Brusa et al. 2007) and radio identifications (Schinnerer et al. 2007), plus a limited number ofGALEX-selected targets (D. Schiminovich et al. 2007, in preparation), are included in the mask design as both…”
GALAXY STELLAR MASS ASSEMBLY BETWEEN 0.2 < z < 2 FROM THE S-COSMOS SURVEY (2009, background): “The 1,887 sources (1% of the total sample) detected with XMM-COSMOS (Hasinger et al. 2007, Brusa et al. 2007, Salvato et al. 2009) were removed from the sample since their optical emissivity is likely dominated by an AGN.”
THE CHANDRA COSMOS SURVEY. III. OPTICAL AND INFRARED IDENTIFICATION OF X-RAY POINT SOURCES (2012, methodology): “It is possible to make a direct comparison with the likelihood threshold values used by Brusa et al. (2007) for XMM-COSMOS because the same input optical catalog was used.”
Deep Spitzer 24 μm COSMOS Imaging. I. The Evolution of Luminous Dusty Galaxies—Confronting the Models (2009, methodology): “The identification of the optical counterparts associated with the remaining 18 XMM objects is considered less secure (Brusa et al. 2007).”
THE XMM-NEWTON WIDE-FIELD SURVEY IN THE COSMOS FIELD (XMM-COSMOS): DEMOGRAPHY AND MULTIWAVELENGTH PROPERTIES OF OBSCURED AND UNOBSCURED LUMINOUS ACTIVE GALACTIC NUCLEI (2010, background): “The present paper, which extends the work presented by Brusa et al. 2007 (hereiafter B07) on the optical identifications of the X–ray point sources in the XMM-COSMOS survey, discusses the multiwavelength properties of this large sample of X-ray selected AGN.”