A survey of hard spectrum ROSAT sources - II. Optical identification of hard sources

Page, M. J.; Mittaz, J. P. D.; Carrera, Francisco J.

doi:10.1046/j.1365-8711.2001.04436.x

Cited by 34 publications

(49 citation statements)

References 34 publications

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“…No object with N H > 10 22 cm À2 shows broad lines in its optical spectrum. Nevertheless, 9% (8/86) of the BL AGNs in our sample do show some intrinsic absorption in their X-ray spectra (see also Mittaz et al 1999;Fiore et al 2001;Page et al 2001;Schartel et al 1997;Tozzi et al 2001;Mainieri et al 2002;Brusa et al 2003;Perola et al 2004;Mateos et al 2005b). In Figure 10 we show the distributions of the RÀK ( Vega) colors for the sources with PL as best-fit model (open histogram) and for the ones that instead require an absorbed power law (hatched histogram).…”

Section: Spectral Properties Of the Samplementioning

confidence: 59%

The XMM‐Newton Wide‐Field Survey in the COSMOS Field. IV. X‐Ray Spectral Properties of Active Galactic Nuclei

Mainieri

Hasinger

Cappelluti

et al. 2007

ASTROPHYS J SUPPL S

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We present a detailed spectral analysis of pointlike X-ray sources in the XMM-Newton COSMOS field. Our sample of 135 sources only includes those that have more than 100 net counts in the 0.3Y10 keV energy band and have been identified through optical spectroscopy. The majority of the sources are well described by a simple power-law model with either no absorption (76%) or a significant intrinsic, absorbing column (20%). The remaining $4% of the sources require a more complex modeling by incorporating additional components to the power law. For sources with more than 180 net counts (bright sample), we allowed both the photon spectral index À and the equivalent hydrogen column N H to be free parameters. For fainter sources, we fix À to the average value and allow N H to vary. The mean spectral index of the 82 sources in the bright sample is À h i ¼ 2:06 AE 0:08, with an intrinsic dispersion of $0.24. Each of these sources has fractional errors on the value of À below 20%. As expected, the distribution of intrinsic absorbing column densities is markedly different between AGNs with or without broad optical emission lines. We find within our sample four type 2 QSO candidates (L X > 10 44 ergs s À1 , N H > 10 22 cm À2 ), with a spectral energy distribution well reproduced by a composite Seyfert 2 spectrum, that demonstrates the strength of the wide-field COSMOS XMM-Newton survey to detect these rare and underrepresented sources. In addition, we have identified a Compton-thick (N H > 1:5 ; 10 24 cm À2 ) AGN at z ¼ 0:1248. Its X-ray spectrum is well fitted by a pure reflection model and a significant Fe K line at rest-frame energy of 6.4 keV.

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Section: Spectral Properties Of the Samplementioning

confidence: 59%

The XMM‐Newton Wide‐Field Survey in the COSMOS Field. IV. X‐Ray Spectral Properties of Active Galactic Nuclei

Mainieri

Hasinger

Cappelluti

et al. 2007

ASTROPHYS J SUPPL S

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“…In addition, we have selected all the HLIRGs (six) from the Stevens et al (2005) sample of high redshift X-ray Compton-thin absorbed QSO. These sources have been observed in X-rays by ROSAT (Page et al 2001) and by XMM-Newton (Page et al 2007), and by SCUBA in the sub-mm band (Page et al 2004). Table 2 presents the most relevant information about the XMM-Newton observations.…”

Section: The Hlirg Samplementioning

confidence: 96%

An XMM-Newtonstudy of hyper-luminous infrared galaxies

Ruiz

Carrera²,

Panessa

2007

A&A

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Aims. Hyper-Luminous Infrared Galaxies (HLIRGs) are the most luminous persistent objects in the Universe. They exhibit extremely high star formation rates, and most of them seem to harbor an Active Galactic Nucleus (AGN). They are unique laboratories to investigate ultimate star formation, and its connection to super-massive black hole growth. X-ray studies of HLIRGs have the potential to unravel the AGN contribution to the bolometric output from these bright objects. Methods. We have selected a sample of 14 HLIRGs observed by XMM-Newton (type 1, type 2 AGN and starburst), 5 of which are candidates to be Compton-thick objects. This is the first time that a systematic study of this type of objects has been carried out in the X-ray spectral band. Their X-ray spectral properties have been correlated with their infrared luminosities, estimated by IRAS, ISO and sub-millimeter observations. Results. The X-ray spectra of HLIRGs present heterogeneous properties. All our X-ray detected HLIRGs (10) have AGN-dominated X-ray spectra. The hard X-ray luminosity of 8 of them is consistent with a pure AGN contribution, while in the remaining 2 sources, both an AGN and a starburst seem to contribute to the overall emission. We found soft excess emission in 5 sources. In one of them it is consistent with a pure starburst origin, while in the other 4 sources it is consistent with an AGN origin. The observed X-ray emission is systematically below that expected for a standard local QSO of the same IR luminosity, suggesting the possible presence of absorption in type 2 objects and/or a departure from a standard spectral energy distribution of QSO. The X-ray-to-IR-luminosity ratio is constant with redshift, indicating similar evolutions for the AGN and starburst component, and that their respective power sources could be physically related.

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“…Therefore the increasing hardness of the source spectra at fainter fluxes observed in the Chandra deep fields (Giacconi et al 2001;Tozzi et al 2001;Brandt et al 2001) is probably due to intrinsic absorption and not to an intrinsically hard power law. Several teams (Della Ceca et al 1999b;Akiyama et al 2000;Fiore et al 2001;Maiolino et al 2001a;Page et al 2001;Reeves et al 2000;Risaliti et al 2001) reported the existence of AGN optically classified as Type-1 but with an indication of absorption in their X-ray spectra. In our sample, there are seven objects with an intrinsic absorption between 10 21 and 10 22 cm −2 which are optically classified as Type-1 AGN.…”

Section: Spectral Parametersmentioning

confidence: 99%

XMM-Newton observation of the Lockman Hole

Mainieri

Bergeron

Hasinger

et al. 2002

A&A

202

295

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Abstract. We present the results of the X-ray spectral analysis of the first deep X-ray survey with the XMM-Newton observatory during Performance Verification. The X-ray data of the Lockman Hole field and the derived cumulative source counts were reported by Hasinger et al. (2001). We restrict the analysis to the sample of 98 sources with more than 70 net counts (flux limit in the [0.5-7] keV band of 1.6 × 10 −15 erg cm −2 s −1 ) of which 61 have redshift identification. We find no correlation between the spectral index Γ and the intrinsic absorption column density N H and, for both the Type-1 and Type-2 AGN populations, we obtain Γ 2. The progressive hardening of the mean X-ray source spectrum with decreasing flux is essentially due to an increase in intrinsic absorption. The marked separation between the two AGN populations in several diagnostics diagrams, involving X-ray colour, X-ray flux, optical/near IR colour and optical brightness, is also a consequence of different absorption column densities and enables the classification of optically faint obscured AGN. The Type-2 and obscured AGN have weaker soft X-ray and optical fluxes and redder R − K colours. They follow the evolutionary tracks of their host galaxies in a colorredshift diagram. About 27% of the subsample with R − K colour are EROs (R − K ≥ 5) and most of these 18 X-ray selected EROs contain an obscured AGN as revealed by their high X-ray-to-optical/near IR flux ratios. There are six sources in our sample with L X [0.5−10] > 10 44 erg s −1 and log(N H ) > 10 22 cm −2 : which are likely Type-2 QSOs and we thus derive a density of ∼69 objects of this class per square degree.

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A survey of hard spectrum ROSAT sources - II. Optical identification of hard sources

Cited by 34 publications

References 34 publications

The XMM‐Newton Wide‐Field Survey in the COSMOS Field. IV. X‐Ray Spectral Properties of Active Galactic Nuclei

The XMM‐Newton Wide‐Field Survey in the COSMOS Field. IV. X‐Ray Spectral Properties of Active Galactic Nuclei

An XMM-Newtonstudy of hyper-luminous infrared galaxies

XMM-Newton observation of the Lockman Hole

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