X‐ray and optical properties of X‐ray sources in the 13hr XMM‐Newton/Chandra deep survey

Page, M. J.; McHardy, I. M.; Gunn, K. F.; Loaring, N. S.; Mason, K. O.; Sasseen, T.; Newsam, A. M.; Ware, A.; Kennea, J. A.; Sekiguchi, K.; Takata, Tadafumi

doi:10.1002/asna.200310026

Cited by 29 publications

(22 citation statements)

References 14 publications

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“…Therefore, the dilution of the AGN light by the host galaxy is mainly occurring at small redshift, supporting the fact that the intrinsic luminosity of the AGN has significantly declined as the redshift is decreasing. Page et al (2003) suggested that if the dilution hypothesis holds true, it may explain why a large fraction of unabsorbed X-ray sources lacking broad emission lines in their optical spectra are lying at a low redshift (the majority of our sources of this kind are lying at z < 0.5). The characteristic luminosity of AGN has declined dramatically (by a factor 10) since z = 2 in both the X-ray (Page et al 1997) and in the optical (Boyle et al 2000).…”

Section: Unabsorbed Agn Lacking Broad Emission Linesmentioning

confidence: 99%

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

Garcet

Gandhi

Gosset

et al. 2007

A&A

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Aims. Our goal is to characterize AGN populations by comparing their X-ray and optical classifications within the framework of the standard orientation-based unified scheme. Methods. We present a sample of 99 spectroscopically identified (R ≤ 22 mag) X-ray selected point sources in the XMM-LSS survey which are significantly detected (≥3σ) in the [2−10] keV band with fluxes between 8 × 10 −15 and 8 × 10 −14 erg s −1 cm −2 , and which have more than 80 counts. We have compared their X-ray and optical classifications. To this end, we performed an X-ray spectral analysis for all of these 99 X-ray sources in order to assess whether they are intrinsically absorbed or not. The X-ray classification is based on the measured intrinsic column density. The optical classification is based on the measured FWHM of the permitted emission lines, the absence of broad lines being due to obscuration within the framework of the standard AGN unified scheme. Results. Introducing the fourfold point correlation coefficient r, we find a mild correlation between the X-ray and the optical classifications (r = 0.28), as up to 32 X-ray sources out of 99 have differing X-ray and optical classifications: on one hand, 10% of the type 1 sources (7/32) present broad emission lines in their optical spectra and strong absorption (N H int ≥ 10 22 cm −2 ) in the X-rays. These objects are highly luminous AGN lying at high redshift and thus dilution effects by the host galaxy light are totally ruled out, their discrepant nature being an intrinsic property instead. Their X-ray luminosities and redshifts distributions are consistent with those of the unabsorbed X-ray sources with broad emission lines (L 2−10 ∼ 4 × 10 44 erg s −1 ; z ∼ 1.9). On the other hand, 25/32 are moderate luminosity (L 2−10 ≤ 5 × 10 43 erg s −1 ) AGN, which are both unabsorbed in the X-rays and only present narrow emission lines in their optical spectra. Based on their line ratios in the optical, the majority of them have an optical spectrum which is more representative of the host galaxy rather than of a reddened AGN. We finally infer that dilution of the AGN by the host galaxy seems to account for their nature. 5/25 have been defined as Seyfert 2 based on their optical spectra. In conclusion, most of these 32 discrepant cases can be accounted for by the standard AGN unified scheme, as its predictions are not met for only 12% of the 99 X-ray sources.

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Section: Unabsorbed Agn Lacking Broad Emission Linesmentioning

confidence: 99%

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

Garcet

Gandhi

Gosset

et al. 2007

A&A

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“…Finally, we have tested whether the lack of optical broad emission lines in unabsorbed NELGs can be explained in terms of AGN/host galaxy contrast (Lumsden et al 2001;Moran et al 2002;Page et al 2003;Severgnini et al 2003). To this end, we have compared the 2-10 keV luminosity distributions of two sub-samples of unabsorbed BLAGNs and NELGs detected with redshifts ranging from 0.17 to 0.7, where the redshift distributions of BLAGNs and NELGs overlap (see Fig.…”

Section: Excess Absorptionmentioning

confidence: 99%

“…Alternatively some objects might host an AGN with a non-standard accretion disk (Yuan & Narayan 2004). A final possibility is that some ALGs may have normal (unabsorbed) AGNs that could be hidden if the host galaxy is bright enough (Severgnini et al 2003;Page et al 2003).…”

Section: Algs X-ray Spectramentioning

confidence: 99%

“…Recent Chandra and XMM-Newton studies have revealed that the widely accepted correlation between the optical obscuration and X-ray absorption (type 1 AGN being unabsorbed and type 2 AGN being absorbed) is not always true. Several cases of type 1 AGN suffering from significant X-ray absorption have been found (Mittaz et al 1999;Fiore et al 2001;Page et al 2001;Schartel et al 2001;Tozzi et al 2001;Mainieri et al 2002;Brusa et al 2003;Page et al 2003;Carrera et al 2004;Perola et al 2004), as well as Seyfert 2 galaxies unabsorbed in X-rays (Pappa et al 2001;Panessa et al 2002;Barcons et al 2003).…”

Section: Introductionmentioning

confidence: 99%

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X-ray spectra of XMM-Newton serendipitous medium flux sources

Mateos

Barcons

Carrera

et al. 2005

A&A

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Abstract. We report on the results of a detailed analysis of the X-ray spectral properties of a large sample of sources detected serendipitously with the XMM-Newton observatory in 25 selected fields, for which optical identification is in progress. The survey covers a total solid angle of ∼3.5 deg 2 and contains 1137 sources with ∼10 −15 < S 0.5−10 < 10 −12 erg cm −2 s −1 with good enough spectral quality as to perform a detailed X-ray spectral analysis of each individual object. We find evidence for hardening of the average X-ray spectra of the sources towards fainter fluxes, and we interpret this as indicating a higher degree of photoelectric absorption amongst the fainter population. Absorption is detected at 95% confidence in 20% of the sources, but it could certainly be present in many other sources below our detection capabilities. For Broad Line AGNs (BLAGNs), we detect absorption in ∼10% of the sources with column densities in the range 10 21 −10 22 cm −2 . The fraction of absorbed Narrow Emission Line galaxies (NELGs, most with intrinsic X-ray luminosities >10 43 erg s −1 , and therefore classified as type 2 AGNs) is significantly higher (40%), with a hint of moderately higher columns. After correcting for absorption, we do not find evidence for a redshift evolution of the underlying power law index of BLAGNs, which stays roughly constant at Γ ∼ 1.9, with intrinsic dispersion of 0.4. A small fraction (∼7%) of BLAGNs and NELGs require the presence of a soft excess, that we model as a black body with temperature ranging from 0.1 to 0.3 keV. Comparing our results on absorption to popular X-ray background synthesis models, we find absorption in only ∼40% of the sources expected. This is due to a deficiency of heavily absorbed sources (with N H ∼ 10 22 −10 24 cm −2 ) in our sample in comparison with the models. We therefore conclude that the synthesis models require some revision in their specific parameters.

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“…However the amount of observational results that cannot be explained in terms of the unified model of AGN is also significant. There is a substantial number of type-1 AGN for which X-ray absorption has been detected (Mittaz et al 1999;Fiore et al 2001;Page et al 2001;Schartel et al 2001;Tozzi et al 2001b;Mainieri et al 2002;Brusa et al 2003;Page et al 2003;Carrera et al 2004;Perola et al 2004;Mateos et al 2005), as well as Seyfert 2 galaxies unabsorbed in X-rays (Pappa et al 2001;Panessa et al 2002;Barcons et al 2003;Mateos et al 2005). The origin of the X-ray absorption in type-1 AGN is still not clear.…”

Section: Introductionmentioning

confidence: 99%

XMM-Newton observations of the Lockman Hole IV: spectra of the brightest AGN

Mateos

Barcons

Carrera

et al. 2005

A&A

110

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This paper presents the results of a detailed X-ray spectral analysis of a sample of 123 X-ray sources detected with XMM-Newton in the Lockman Hole field. This is the deepest observation carried out with XMM-Newton with more that 600 ks of good EPIC-pn data. We have spectra with good signal to noise (>500 source counts) for all objects down to 0.2−12 keV fluxes of ∼5 × 10 −15 erg cm −2 s −1 (flux limit of ∼6 × 10 −16 erg cm −2 s −1 in the 0.5−2 and 2−10 keV bands). At the time of the analysis, we had optical spectroscopic identifications for 60% of the sources, 46 being optical type-1 AGN and 28 optical type-2 AGN. Using a single power law model our sources' average spectral slope hardens at faint 0.5−2 keV fluxes but not at faint 2−10 keV fluxes. We have been able to explain this effect in terms of an increase in X-ray absorption at faint fluxes. We did not find in our data any evidence for the existence of a population of faint intrinsically harder sources. The average spectral slope of our sources is ∼1.9, with an intrinsic dispersion of ∼0.28. We detected X-ray absorption (F-test significance ≥95%) in 37% of the sources, ∼10% in type-1 AGN (rest-frame N H ∼ 1.6 × 10 21 −1.2 × 10 22 cm −2 ) and ∼77% (rest-frame N H ∼ 1.5 × 10 21 −4 × 10 23 cm −2 ) in type-2 AGN. Using X-ray fluxes corrected for absorption, the fraction of absorbed objects and the absorbing column density distribution did not vary with X-ray flux. Our type-1 and type-2 AGN do not appear to have different continuum shapes, but the distribution of intrinsic (rest-frame) absorbing column densities is different among both classes. A significant fraction of our type-2 AGN (5 out of 28) were found to display no substantial absorption (N H < 10 21 cm −2 ). We discuss possible interpretations to this in terms of Compton-thick AGN and intrinsic Broad Line Region properties. An emission line compatible with Fe Kα was detected in 8 sources (1 type-1 AGN, 5 type-2 AGN and 2 unidentified) with rest frame equivalent widths 120−1000 eV. However weak broad components can be easily missed in other sources by the relatively noisy data. The AGN continuum or intrinsic absorption did not depend on X-ray luminosity and/or redshift. Soft excess emission was detected in 18 objects, but only in 9 (including 4 type-1 AGN and 4 type-2 AGN) could we fit this spectral component with a black body model. The measured 0.5−2 keV luminosities of the fitted black body were not significantly different in type-1 and type-2 AGN, although the temperatures of the black body were slightly higher in type-2 AGN ( kT = 0.26 ± 0.08) than in type-1 AGN ( kT = 0.09 ± 0.01). For 9 sources (including 1 type-1 AGN and 3 type-2 AGN) a scattering model provided a better fit of the soft excess emission. We found that the integrated contribution from our sources to the X-ray background in the 2−7 keV band is softer (Γ = 1.5−1.6) than the background itself, implying that fainter sources need to be more absorbed.

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X‐ray and optical properties of X‐ray sources in the 13hr XMM‐Newton/Chandra deep survey

Cited by 29 publications

References 14 publications

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

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

X-ray spectra of XMM-Newton serendipitous medium flux sources

XMM-Newton observations of the Lockman Hole IV: spectra of the brightest AGN

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