Optical and infrared properties of active galactic nuclei in the Lockman Hole

Rovilos, E.; Fotopoulou, S.; Salvato, M.; Burwitz, V.; Egami, E.; Hasinger, G.; Szokoly, G.

doi:10.1051/0004-6361/201015763

Cited by 20 publications

(22 citation statements)

References 106 publications

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“…However, there is a dependency of both the reliability and the efficiency of the method with the flux limits used, as previously claimed (e.g. Barmby et al 2006;Brusa et al 2009;Rovilos et al 2011;Mendez et al 2013).…”

Section: Wise Colour-colour Selectionmentioning

confidence: 67%

A wide search for obscured active galactic nuclei using XMM–Newton and WISE

Rovilos¹,

Georgantopoulos²,

Akylas³

et al. 2013

Monthly Notices of the Royal Astronomical Society

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Heavily obscured and Compton-thick AGN are missing even in the deepest X-ray surveys, and indirect methods are required to detect them. Here we use a combination of the XMM-Newton serendipitous X-ray survey with the optical SDSS, and the infrared WISE all-sky survey in order to check the efficiency of the low X-ray to infrared luminosity selection method in finding heavily obscured AGN. We select the sources which are detected in the hard X-ray band (2 − 8 keV), and also have a redshift determination (photometric or spectroscopic) in the SDSS catalogue. We match this sample with the WISE catalogue, and fit the spectral energy distributions (SEDs) of the 2 844 sources which have three, or more, photometric data-points in the infrared. We then select the heavily obscured AGN candidates by comparing their 12 µm AGN luminosity to the observed 2-10 keV X-ray luminosity and the intrinsic relation between the X-ray and the midinfrared luminosities. With this approach we find 20 candidate heavily obscured AGN and we then examine their X-ray and optical spectra. Of the 20 initial candidates, we find nine (64%; out of the 14, for which X-ray spectra could be fit) based on the X-ray spectra, and seven (78%; out of the nine detected spectroscopically in the SDSS) based on the [OIII] line fluxes. Combining all criteria, we determine the final number of heavily obscured AGN to be 12-19, and the number of Compton-thick AGN to be 2-5, showing that the method is reliable in finding obscured AGN, but not Compton-thick. However those numbers are smaller than what would be expected from X-ray background population synthesis models, which demonstrates how the optical-infrared selection and the scatter of the L x −L MIR relation introduced by observational constraints limit the efficiency of the method. Finally, we test popular obscured AGN selection methods based on midinfrared colours, and find that the probability of an AGN to be selected by its mid-infrared colours increases with the X-ray luminosity. The (observed) X-ray luminosities of heavily obscured AGN are relatively low (L 2−10keV < 10 44 erg s −1 ), even though most of them are located in the "QSO locus". However, a selection scheme based on a relatively low X-ray luminosity and mid-infrared colours characteristic of QSOs would not select ∼ 25% of the heavily obscured AGN of our sample.

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Section: Wise Colour-colour Selectionmentioning

confidence: 67%

A wide search for obscured active galactic nuclei using XMM–Newton and WISE

Rovilos¹,

Georgantopoulos²,

Akylas³

et al. 2013

Monthly Notices of the Royal Astronomical Society

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“…In current NuSTAR surveys (generally 10-20 positions; e.g., Harrison et al 2013), the detected sources are typically first matched to Chandra/XMM-Newton (or other X-ray) sources which then are matched to optical/NIR/MIR counterparts. The X-ray sources found in the surveys listed in Table 1 span an extremely broad range of optical/NIR/MIR flux; e.g., the I-band magnitudes for AGNs range from brighter than 15th to fainter than 28th magnitude (e.g., Barger et al 2003b;Szokoly et al 2004;Laird et al 2009;Brusa et al 2010;Luo et al 2010;Pineau et al 2011;Rovilos et al 2011;Xue et al 2011;Trichas et al 2012). Fig.…”

Section: Supporting Multiwavelength Observations and Spectroscopic Fomentioning

confidence: 99%

Cosmic X-ray surveys of distant active galaxies

Brandt

Alexander

2015

Astron Astrophys Rev

315

227

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We review results from cosmic X-ray surveys of active galactic nuclei (AGNs) over the past ≈ 15 yr that have dramatically improved our understanding of growing supermassive black holes in the distant universe. First, we discuss the utility of such surveys for AGN investigations and the capabilities of the missions making these surveys, emphasizing Chandra, XMM-Newton, and NuSTAR. Second, we briefly describe the main cosmic X-ray surveys, the essential roles of complementary multiwavelength data, and how AGNs are selected from these surveys. We then review key results from these surveys on the AGN population and its evolution ("demographics"), the physical processes operating in AGNs ("physics"), and the interactions between AGNs and their environments ("ecology"). We conclude by describing some significant unresolved questions and prospects for advancing the field.

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“…With respect to simpler matching approaches, based only on the positional offset between sources in different catalogs, the likelihood ratio technique has the advantage of taking into account, for each possible counterpart, the probability that it is a real or a spurious identification, allowing a much better statistical characterization of the final sample of identifications. This powerful statistical method has become common recently and has been applied first to radio surveys (Ciliegi et al 2005) and to several medium and faint Chandra and XMM-Newton surveys (Cardamone et al 2008, Laird et al 2009, Aird et al 2010, Luo et al 2010, Brusa et al 2010, Rovilos et al 2011.…”

Section: Identification Datasetsmentioning

confidence: 99%

THE CHANDRA COSMOS SURVEY. III. OPTICAL AND INFRARED IDENTIFICATION OF X-RAY POINT SOURCES

Civano

Elvis

Brusa

et al. 2012

ApJS

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223

278

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The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.9 deg 2 of the COSMOS field down to limiting depths of 1.9×10 −16 erg cm −2 s −1 in the soft (0.5-2 keV) band, 7.3×10 −16 erg cm −2 s −1 in the hard (2-10 keV) band, and 5.7×10 −16 erg cm −2 s −1 in the full (0.5-10 keV) band. In this paper we report the i, K and 3.6µm identifications of the 1761 X-ray point sources. We use the likelihood ratio technique to derive the association of optical/infrared counterparts for 97% of the X-ray sources. For most of the remaining 3% , the presence of multiple counterparts or the faintness of the possible counterpart prevented a unique association. For only 10 X-ray sources we were not able to associate a counterpart, mostly due to the presence of a very bright field source close by. Only 2 sources are truly empty fields. The full catalog, including spectroscopic and photometric redshifts and classification described here in detail, is available on-line. Making use of the large number of X-ray sources, we update the "classic locus" of AGN defined 20 years ago in soft X-ray surveys and define a new locus containing 90% of the AGN in the survey with full band luminosity >10 42 erg s −1 . We present the linear fit between the total i band magnitude and the X-ray flux in the soft and hard band, drawn over 2 orders of magnitude in X-ray flux, obtained using the combined C-COSMOS and XMM-COSMOS samples. We focus on the X-ray to optical flux ratio (X/O) and we test its known correlation with redshift and luminosity, and a recently introduced anti-correlation with the concentration index (C). We find a strong anti-correlation (though the dispersion is of the order of 0.5 dex) between C and X/O, computed in the hard band, and that 90% of the obscured AGN in the sample with morphological information live in galaxies with regular morphology (bulgy and disky/spiral), suggesting that secular processes govern a significant fraction of the BH growth at X-ray luminosities of 10 43 − 10 44.5 erg s −1 . We also investigate the degree of obscuration of the sample, using the hardness ratio and we compare the X-ray color with the near-infrared-to-optical one.

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Optical and infrared properties of active galactic nuclei in the Lockman Hole

Cited by 20 publications

References 106 publications

A wide search for obscured active galactic nuclei using XMM–Newton and WISE

A wide search for obscured active galactic nuclei using XMM–Newton and WISE

Cosmic X-ray surveys of distant active galaxies

THE CHANDRA COSMOS SURVEY. III. OPTICAL AND INFRARED IDENTIFICATION OF X-RAY POINT SOURCES

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