The XMM large scale structure survey: optical vs. X-ray classifications of active galactic nuclei and the unified scheme

Garcet, O.; Gandhi, P.; Gosset, Éric; Sprimont, Pierre-Guillaume; Surdej, Jean; Borkowski, V.; Tajer, M.; Pacaud, F.; Pierre, M.; Chiappetti, L.; Maccagni, D.; Page, M. J.; Carrera, Francisco J.; Tedds, J. A.; Mateos, S.; Krumpe, M.; Contini, T.; Corral, A.; Ebrero, J.; Gavignaud, I.; Schwope, A. D.; Fèvre, O. Le; Polletta, M.; Rosen, S. R.; Lonsdale, C. J.; Watson, M. G.; Borczyk, W.; Vaïsänen, P.

doi:10.1051/0004-6361:20077778

Cited by 38 publications

(54 citation statements)

References 80 publications

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“…However, Risaliti et al (1999) found an even smaller fraction of only 4%. On the contrary, Marinucci et al (2012) claimed that the fraction of unobscured Sy2 in their sample in about 40% and Page et al (2006) and Garcet et al (2007) reported an even higher fraction of about 66%−68%.…”

Section: Introductionmentioning

confidence: 95%

A new sample of X-ray selected narrow emission-line galaxies

Pons

Watson

2016

A&A

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A sample of X-ray and optically selected narrow emission-line galaxies (769 sources) from the 3XMM catalogue cross-correlated with SDSS (DR9) catalogue has been studied. Narrow-emission line active galactic nuclei (AGN; type-2) have been selected on the basis of their emission line ratios and/or X-ray luminosity. We have looked for X-ray unobscured type-2 AGN. As X-ray spectra were not available for our whole sample, we have checked the reliability of using the X-ray hardness ratio (HR) as a probe of the level of obscuration and we found a very good agreement with full spectral fitting results, with only 2% of the sources with apparently unobscured HR turning out to have an obscured spectrum. Despite the fact that type-2 AGN are supposed to be absorbed based on the Unified Model, about 60% of them show no sign or very low level of X-ray obscuration. After subtraction of contaminants to the sample, that is Narrow-Line Seyfert 1 and Compton-thick AGN, the fraction of unobscured Sy2 drops to 47%. For these sources, we were able to rule out dust reddening and variability for most of them as an explanation of the absence of optical broad emission-lines. The main explanations remaining are the dilution of weak/very broad emission-lines by the host galaxy and the intrinsic absence of the broad-line region (BLR) due to low accretion rates (i.e. True Sy2). However, the number of True Sy2 strongly depends on the method used to verify the intrinsic lack of broad lines. Indeed using the optical continuum luminosity to predict the BLR properties gives a much larger fraction of True Sy2 (about 90% of the unobscured Sy2 sample) than the use of the X-ray 2 keV luminosity (about 20%). Nevertheless the number of AGN we securely detected as True Sy2 is at least three times larger that the previously confirmed number of True Sy2.

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Section: Introductionmentioning

confidence: 95%

A new sample of X-ray selected narrow emission-line galaxies

Pons

Watson

2016

A&A

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“…We also report in this diagram the values obtained for a sample of the brightest 99 hard X-ray sources detected in the XMM-LSS survey (e.g. Garcet et al 2007). This survey covers ∼6 deg 2 and, therefore, is one of the surveys with the widest coverage area in X-rays.…”

Section: X-ray To Optical Flux Ratiomentioning

confidence: 99%

Revealing X-ray obscured quasars in SWIRE sources with extreme mid-IR/optical flux ratios

Lanzuisi

Piconcelli²,

Fiore³

et al. 2009

A&A

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Recent works have suggested that selection criteria based on mid-IR properties, i.e. extreme colors and bright flux levels, can be used to reveal a population of dust-enshrouded, extremely-luminous quasars at z ∼ 1-2. However, the X-ray spectral properties of these intriguing objects still remain largely unexplored. We have performed an X-ray study of a large sample of bright mid-IR (F 24 μm > 1.3 mJy) galaxies showing an extreme MIR/Optical flux ratio (F 24 μm /F R > 2000) in order to confirm the presence of a luminous active nucleus in these very red objects. Sampling of a large area is required to pick up objects at the highest luminosities given their low surface density. Accordingly, we have applied our selection criteria to an area of ∼6 deg 2 covered by XMM-Newton/Chandra observations within the ∼50 deg 2 SWIRE survey, resulting in a final sample of 44 objects. The vast majority of the source redshifts, both spectroscopic and photometric, are in the range 0.7 < ∼ z < ∼ 2.5. The X-ray coverage of the sample is highly inhomogeneous (from snap-shot 5 ks Chandra observations to medium-deep XMM-Newton exposures of 70 ks) and, consequently, a sizable fraction of them (≈43%) remains undetected in the 0.5-10 keV band. Using spectral or hardness information we were able to estimate the value of the absorbing column density in 23 sources. 95% of them are consistent with being obscured by neutral gas with an intrinsic column density of N H ≥ 10 22 cm −2 . Remarkably, we also find that ∼55% of these sources can be classified as type 2 quasars on the basis of their absorption properties and X-ray luminosity. Moreover, most of the X-ray undetected sources show extreme mid-IR colors, consistent with being luminous AGN-powered objects, suggesting they might host heavily obscured (possibly Compton-thick) quasars in X-rays. This demonstrates that our selection criteria applied to a wide area survey is very efficient in finding a large number of type 2 quasars at z > ∼ 1. The existence of this class of very powerful, obscured quasars at high z could have important implications in the context of the formation and cosmological evolution of accreting supermassive black holes and their host galaxies.

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“…The median value of probXO for ext, ptl, stars, and mcl objects is 0.018, 0.009, 0.0002 and 0.109, respectively. Tajer et al (2007) and Garcet et al (2007) ranked the probability of counterparts as good (probXY < 0.01), fair (0.01 < probXY < 0.03) and bad (probXY > 0.03). We thus see that our mcl objects naturally fall in the latter category.…”

Section: The Sample Of X-ray Sources and Their Counterpartsmentioning

confidence: 99%

“…deg XMM-Large Scale Structure (LSS) medium-deep extragalactic survey. Earlier versions of our survey over a lower solid angle and a variety of analyses can be found in Chiappetti et al (2005), Gandhi et al (2006), Pierre et al (2007), Tajer et al (2007), Polletta et al (2007), Garcet et al (2007), Tasse et al (2008a,b) and Nakos et al (2009).…”

Section: Introductionmentioning

confidence: 99%

Classification and environmental properties of X-ray selected point-like sources in the XMM-LSS field

Мelnyk

Plionis

Elyiv

et al. 2013

A&A

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Context. The XMM-Large Scale Structure survey, covering an area of 11.1 sq. deg., contains more than 6000 X-ray point-like sources detected with the XMM-Newton to a flux of 3 × 10 −15 erg s −1 cm −2 in the [0.5−2] keV band. The vast majority of these sources have optical (CFHTLS), infrared (SWIRE IRAC and MIPS), near-infrared (UKIDSS), and/or ultraviolet (GALEX) counterparts. Aims. We wish to investigate the environmental properties of the different types of the XMM-LSS X-ray sources by defining their environment using the i -band CFHTLS W1 catalog of optical galaxies to a magnitude limit of 23.5 mag. Methods. We have classified 4435 X-ray selected sources on the basis of their spectra, SEDs, and X-ray luminosity, and estimated their photometric redshifts, which have a 4−11 band photometry with an accuracy of σ z/(1+zsp) = 0.076 with 22.6% outliers for i < 26 mag. We estimated the local overdensities of 777 X-ray sources that have spectro-z or photo-z calculated by using more than seven bands (accuracy of σ z/(1+zsp) = 0.061 with 13.8% outliers) within the volume-limited region defined by 0.1 ≤ z ≤ 0.85 and −23.5 < M i < −20. Results. Although X-ray sources may be found in variety of environments, a high fraction ( > ∼ 55−60%), as verified by comparing with the random expectations, reside in overdense regions. The galaxy overdensities within which X-ray sources reside show a positive recent redshift evolution (at least for the range studied; z < ∼ 0.85). We also find that X-ray selected galaxies, when compared to AGN, inhabit significantly higher galaxy overdensities, although their spatial extent appear to be smaller than that of AGN. Hard AGN (HR ≥ −0.2) are located in more overdense regions than soft AGN (HR < −0.2), which is clearly seen in both redshift ranges, although it appears to be stronger in the higher redshift range (0.55 < z < 0.85). Furthermore, the galaxy overdensities (with δ > ∼ 1.5) within which soft AGN are embedded appear to evolve more rapidly compared to the corresponding overdensities around hard AGN.

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The XMM large scale structure survey: optical vs. X-ray classifications of active galactic nuclei and the unified scheme

Cited by 38 publications

References 80 publications

A new sample of X-ray selected narrow emission-line galaxies

A new sample of X-ray selected narrow emission-line galaxies

Revealing X-ray obscured quasars in SWIRE sources with extreme mid-IR/optical flux ratios

Classification and environmental properties of X-ray selected point-like sources in the XMM-LSS field

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