References of "Pierre, M"
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See detailThe XXL survey: First results and future
Pierre, M.; Adami, C.; Birkinshaw, M. et al

in Astronomische Nachrichten (2017), 338

The XXL survey currently covers two 25 sq. deg. patches with XMM observations of ~10ks. We summarise the scientific results associated with the first release of the XXL data set, that occurred mid 2016 ... [more ▼]

The XXL survey currently covers two 25 sq. deg. patches with XMM observations of ~10ks. We summarise the scientific results associated with the first release of the XXL data set, that occurred mid 2016. We review several arguments for increasing the survey depth to 40 ks during the next decade of XMM operations. X-ray (z<2) cluster, (z<4) AGN and cosmic background survey science will then benefit from an extraordinary data reservoir. This, combined with deep multi-$\lambda$ observations, will lead to solid standalone cosmological constraints and provide a wealth of information on the formation and evolution of AGN, clusters and the X-ray background. In particular, it will offer a unique opportunity to pinpoint the z>1 cluster density. It will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA and Euclid missions. [less ▲]

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See detailThe XXL Survey: I. Scientific motivations - XMM-Newton observing plan - Follow-up observations and simulation programme
Pierre, M.; Pacaud, F.; Adami, C. et al

in Astronomy and Astrophysics (2016), 592

Context. The quest for the cosmological parameters that describe our universe continues to motivate the scientific community to undertake very large survey initiatives across the electromagnetic spectrum ... [more ▼]

Context. The quest for the cosmological parameters that describe our universe continues to motivate the scientific community to undertake very large survey initiatives across the electromagnetic spectrum. Over the past two decades, the Chandra and XMM-Newton observatories have supported numerous studies of X-ray-selected clusters of galaxies, active galactic nuclei (AGNs), and the X-ray background. The present paper is the first in a series reporting results of the XXL-XMM survey; it comes at a time when the Planck mission results are being finalised. Aims. We present the XXL Survey, the largest XMM programme totaling some 6.9 Ms to date and involving an international consortium of roughly 100 members. The XXL Survey covers two extragalactic areas of 25 deg2 each at a point-source sensitivity of ∼5 × 10-15 erg s-1 cm-2 in the [0.5-2] keV band (completeness limit). The survey's main goals are to provide constraints on the dark energy equation of state from the space-time distribution of clusters of galaxies and to serve as a pathfinder for future, wide-area X-ray missions. We review science objectives, including cluster studies, AGN evolution, and large-scale structure, that are being conducted with the support of approximately 30 follow-up programmes. Methods. We describe the 542 XMM observations along with the associated multi-λ and numerical simulation programmes. We give a detailed account of the X-ray processing steps and describe innovative tools being developed for the cosmological analysis. Results. The paper provides a thorough evaluation of the X-ray data, including quality controls, photon statistics, exposure and background maps, and sky coverage. Source catalogue construction and multi-λ associations are briefly described. This material will be the basis for the calculation of the cluster and AGN selection functions, critical elements of the cosmological and science analyses. Conclusions. The XXL multi-λ data set will have a unique lasting legacy value for cosmological and extragalactic studies and will serve as a calibration resource for future dark energy studies with clusters and other X-ray selected sources. With the present article, we release the XMM XXL photon and smoothed images along with the corresponding exposure maps. © ESO, 2016. [less ▲]

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See detailThe XXL Survey XIV. AAOmega Redshifts for the Southern XXL Field
Lidman, C.; Ardila, F.; Owers, M. et al

in Publications of the Astronomical Society of Australia (2016), 33

We present a catalogue containing the redshifts of 3 660 X-ray selected targets in the XXL southern field. The redshifts were obtained with the AAOmega spectrograph and 2dF fibre positioner on the Anglo ... [more ▼]

We present a catalogue containing the redshifts of 3 660 X-ray selected targets in the XXL southern field. The redshifts were obtained with the AAOmega spectrograph and 2dF fibre positioner on the Anglo-Australian Telescope. The catalogue contains 1 515 broad line AGN, 528 stars, and redshifts for 41 out of the 49 brightest X-ray selected clusters in the XXL southern field. Copyright © Astronomical Society of Australia 2016. [less ▲]

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See detailThe XXL Survey: XII. Optical spectroscopy of X-ray-selected clusters and the frequency of AGN in superclusters
Koulouridis, E.; Poggianti, B.; Altieri, B. et al

in Astronomy and Astrophysics (2016), 592

Context. This article belongs to the first series of XXL publications. It presents multifibre spectroscopic observations of three 0.55 deg2 fields in the XXL Survey, which were selected on the basis of ... [more ▼]

Context. This article belongs to the first series of XXL publications. It presents multifibre spectroscopic observations of three 0.55 deg2 fields in the XXL Survey, which were selected on the basis of their high density of X-ray-detected clusters. The observations were obtained with the AutoFib2+WYFFOS (AF2) wide-field fibre spectrograph mounted on the 4.2 m William Herschel Telescope. Aims. The paper first describes the scientific rationale, the preparation, the data reduction, and the results of the observations, and then presents a study of active galactic nuclei (AGN) within three superclusters. Methods. To determine the redshift of galaxy clusters and AGN, we assign high priority to a) the brightest cluster galaxies (BCGs), b) the most probable cluster galaxy candidates, and c) the optical counterparts of X-ray point-like sources. We use the outcome of the observations to study the projected (2D) and the spatial (3D) overdensity of AGN in three superclusters. Results. We obtained redshifts for 455 galaxies in total, 56 of which are counterparts of X-ray point-like sources. We were able to determine the redshift of the merging supercluster XLSSC-e, which consists of six individual clusters at z ~ 0.43, and we confirmed the redshift of supercluster XLSSC-d at z ~ 0.3. More importantly, we discovered a new supercluster, XLSSC-f, that comprises three galaxy clusters also at z ~ 0.3. We find a significant 2D overdensity of X-ray point-like sources only around the supercluster XLSSC-f. This result is also supported by the spatial (3D) analysis of XLSSC-f, where we find four AGN with compatible spectroscopic redshifts and possibly one more with compatible photometric redshift. In addition, we find two AGN (3D analysis) at the redshift of XLSSC-e, but no AGN in XLSSC-d. Comparing these findings with the optical galaxy overdensity we conclude that the total number of AGN in the area of the three superclusters significantly exceeds the field expectations. All of the AGN found have luminosities below 7 × 1042 erg s-1. Conclusions. The difference in the AGN frequency between the three superclusters cannot be explained by the present study because of small number statistics. Further analysis of a larger number of superclusters within the 50 deg2 of the XXL is needed before any conclusions on the effect of the supercluster environment on AGN can be reached. © ESO, 2016. [less ▲]

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See detailSearch for gravitational lens candidates in the XMM-LSS/CFHTLS common field
Elyiv, A.; Melnyk, O.; Finet, F. et al

in Monthly Notices of the Royal Astronomical Society (2013), 434

Our aim was to identify gravitational lens candidates among some 5500 optical counterparts of the X-ray point-like sources in the medium-deep ˜11 deg[SUP]2[/SUP] XMM-LSS survey. We have visually inspected ... [more ▼]

Our aim was to identify gravitational lens candidates among some 5500 optical counterparts of the X-ray point-like sources in the medium-deep ˜11 deg[SUP]2[/SUP] XMM-LSS survey. We have visually inspected the optical counterparts of each QSOs/AGN using CFHTLS T006 images. We have selected compact pairs and groups of sources which could be multiply imaged QSO/AGN. We have measured the colours and characterized the morphological types of the selected sources using the multiple point spread function fitting technique. We found three good gravitational lens candidates: J021511.4-034306, J022234.3-031616 and J022607.0-040301 which consist of pairs of point-like sources having similar colours. On the basis of a colour-colour diagram and X-ray properties we could verify that all these sources are good QSO/AGN candidates rather than stars. Additional secondary gravitational lens candidates are also reported. [less ▲]

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See detailClassification and environmental properties of X-ray selected point-like sources in the XMM-LSS field
Melnyk, Olga ULiege; Plionis, M.; Elyiv, Andrii ULiege et al

in Astronomy and Astrophysics (2013), 557(A81),

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See detailThe XMM-LSS catalogue: X-ray sources and associated multiwavelength data. Version II
Chiappetti, L.; Clerc, N.; Pacaud, F. et al

in Monthly Notices of the Royal Astronomical Society (2013), 429

We present the final release of the multi-wavelength XMM-LSS data set,covering the full survey area of 11.1 square degrees, with X-ray data processed with the latest XMM-LSS pipeline version. The present ... [more ▼]

We present the final release of the multi-wavelength XMM-LSS data set,covering the full survey area of 11.1 square degrees, with X-ray data processed with the latest XMM-LSS pipeline version. The present publication supersedes the Pierre et al.(2007) catalogue pertaining to the initial 5 square degrees. We provide X-ray source lists in the customary energy bands (0.5-2 and 2-10 keV) for a total of 6721 objects in the deep full-exposure catalogue and 5572 in the 10ks-limited one, above a detection likelihood of 15 in at least one band. We also provide a multiwavelength catalogue, cross-correlating our list with IR, NIR, optical and UV catalogues. Customary data products (X-ray FITS images, CFHTLS and SWIRE thumbnail images) are made available together with our interactively queriable database in Milan, while a static snapshot of the catalogues will be supplied to CDS, as soon as final acceptance is completed. [less ▲]

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See detailClassification, photo-z and environment of X-ray selected sources in the XMM-LSS field
Melnyk, Olga ULiege; Plionis, M; Elyiv, Andrii ULiege et al

in Proceedings of the XXL Consortium meeting in the Castle of the Meudon observatory, from 9 to 13 July, 2012 (2012, July 09)

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See detailAngular correlation functions of X-ray point-like sources in the full exposure XMM-LSS field
Elyiv, Andrii ULiege; Clerc, N.; Plionis, M. et al

in Astronomy and Astrophysics (2012), 537

<BR /> Aims: Our aim is to study the large-scale structure of different types of AGN using the medium-deep XMM-LSS survey. <BR /> Methods: We measure the two-point angular correlation function of 5700 and ... [more ▼]

<BR /> Aims: Our aim is to study the large-scale structure of different types of AGN using the medium-deep XMM-LSS survey. <BR /> Methods: We measure the two-point angular correlation function of 5700 and 2500 X-ray point-like sources over the 11 sq. deg. XMM-LSS field in the soft (0.5-2 keV) and hard (2-10 keV) bands. For the conversion from the angular to the spatial correlation function we used the Limber integral equation and the luminosity-dependent density evolution model of the AGN X-ray luminosity function. <BR /> Results: We have found significant angular correlations with the power-law parameters γ = 1.81 ± 0.02, θ[SUB]0[/SUB] = 1.3'' ± 0.2'' for the soft, and γ = 2.00 ± 0.04, θ[SUB]0[/SUB] = 7.3'' ± 1.0'' for the hard bands. The amplitude of the correlation function w(θ) is higher in the hard than in the soft band for f[SUB]x[/SUB] ≲ 10[SUP]-14[/SUP] erg s[SUP]-1[/SUP] cm[SUP]-2[/SUP] and lower above this flux limit. We confirm that the clustering strength θ[SUB]0[/SUB] grows with the flux limit of the sample, a trend which is also present in the amplitude of the spatial correlation function, but only for the soft band. In the hard band, it remains almost constant with r[SUB]0[/SUB] ≃ 10h[SUP]-1[/SUP] Mpc, irrespective of the flux limit. Our analysis of AGN subsamples with different hardness ratios shows that the sources with a hard-spectrum are more clustered than soft-spectrum ones. This result may be a hint that the two main types of AGN populate different environments. Finally, we find that our clustering results correspond to an X-ray selected AGN bias factor of 2.5 for the soft band sources (at a median <inline-formula>bar{z} ≃ 1.1) and 3.3 for the hard band sources (at a median <inline-formula>bar{z} ≃ 1), which translates into a host dark matter halo mass of 10[SUP]13[/SUP]h[SUP]-1[/SUP]M[SUB]&sun;[/SUB] and 10[SUP]13.7[/SUP]h[SUP]-1[/SUP]M[SUB]&sun;[/SUB] for the soft and hard bands, respectively. This paper is dedicated to the memory of Olivier Garcet who has initiated the present work just before his sudden death. [less ▲]

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See detailThe XMM-LSS survey: optical assessment and properties of different X-ray selected cluster classes
Adami, C.; Mazure, A.; Pierre, M. et al

in Astronomy and Astrophysics (2011), 526(A18), 36

XMM and Chandra opened a new area for the study of clusters of galaxies. Not only for cluster physics but also, for the detection of faint and distant clusters that were inaccessible with previous ... [more ▼]

XMM and Chandra opened a new area for the study of clusters of galaxies. Not only for cluster physics but also, for the detection of faint and distant clusters that were inaccessible with previous missions. This article presents 66 spectroscopically confirmed clusters (0.05<z<1.5) within an area of 6 deg2 enclosed in the XMM-LSS survey. Almost two thirds have been confirmed with dedicated spectroscopy only and 10% have been confirmed with dedicated spectroscopy supplemented by literature redshifts. Sub-samples, or classes, of extended-sources are defined in a two-dimensional X-ray parameter space allowing for various degrees of completeness and contamination. We describe the procedure developed to assess the reality of these cluster candidates using the CFHTLS photometric data and spectroscopic information from our own follow-up campaigns. Most of these objects are low mass clusters, hence constituting a still poorly studied population. In a second step, we quantify correlations between the optical properties such as richness or velocity dispersion and the cluster X-ray luminosities. We examine the relation of the clusters to the cosmic web. Finally, we review peculiar structures in the surveyed area like very distant clusters and fossil groups. [less ▲]

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See detailThe COSPIX mission: focusing on the energetic and obscured Universe
Ferrando, P.; Goldwurm, A.; Laurent, P. et al

in Rieger, F.; van Eldik, C. (Eds.) 25th Texas Symposium on Relativistic Astrophysics (2011, April 01)

Tracing the formation and evolution of all supermassive black holes, including the obscured ones, understanding how black holes influence their surroundings and how matter behaves under extreme conditions ... [more ▼]

Tracing the formation and evolution of all supermassive black holes, including the obscured ones, understanding how black holes influence their surroundings and how matter behaves under extreme conditions, are recognized as key science objectives to be addressed by the next generation of instruments. These are the main goals of the COSPIX proposal, made to ESA in December 2010 in the context of its call for selection of the M3 mission. In addition, COSPIX, will also provide key measurements on the non thermal Universe, particularly in relation to the question of the acceleration of particles, as well as on many other fundamental questions as for example the energetic particle content of clusters of galaxies. COSPIX is proposed as an observatory operating from 0.3 to more than 100 keV. The payload features a single long focal length focusing telescope offering an effective area close to ten times larger than any scheduled focusing mission at 30 keV, an angular resolution better than 20 arcseconds in hard X-rays, and polarimetric capabilities within the same focal plane instrumentation. In this paper, we describe the science objectives of the mission, its baseline design, and its performances, as proposed to ESA. [less ▲]

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See detailA multi-wavelength survey of AGN in the XMM-LSS field. I. Quasar selection via the KX technique
Nakos, Theodoros; Willis, J. P.; Andreon, S. et al

in Astronomy and Astrophysics (2009), 494

Aims. We present a sample of candidate quasars selected using the KX-technique. The data cover 0.68 deg[SUP]2[/SUP] of the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey area where ... [more ▼]

Aims. We present a sample of candidate quasars selected using the KX-technique. The data cover 0.68 deg[SUP]2[/SUP] of the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey area where overlapping multi-wavelength imaging data permits an investigation of the physical nature of selected sources. Methods: The KX method identifies quasars on the basis of their optical (R and z') to near-infrared (K_s) photometry and point-like morphology. We combine these data with optical (u^*,g', r',i',z') and mid-infrared (3.6-24 mum) wavebands to reconstruct the spectral energy distributions (SEDs) of candidate quasars. Results: Of 93 sources selected as candidate quasars by the KX method, 25 are classified as quasars by the subsequent SED analysis. Spectroscopic observations are available for 12/25 of these sources and confirm the quasar hypothesis in each case. Even more, 90% of the SED-classified quasars show X-ray emission, a property not shared by any of the false candidates in the KX-selected sample. Applying a photometric redshift analysis to the sources without spectroscopy indicates that the 25 sources classified as quasars occupy the interval 0.7 <= z <= 2.5. The remaining 68/93 sources are classified as stars and unresolved galaxies. [less ▲]

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See detailThe XMM-LSS survey: the Class 1 cluster sample over the initial 5 deg(2) and its cosmological modelling
Pacaud, F.; Pierre, M.; Adami, C. et al

in Monthly Notices of the Royal Astronomical Society (2007), 382(3), 1289-1308

We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area of some 5 deg(2) out to a redshift of z = 1.05. The sample clusters, which represent about half of the X-ray clusters ... [more ▼]

We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area of some 5 deg(2) out to a redshift of z = 1.05. The sample clusters, which represent about half of the X-ray clusters identified in the region, follow well-defined X-ray selection criteria and are all spectroscopically confirmed. For all clusters, we provide X-ray luminosities and temperatures as well as masses, obtained from dedicated spatial and spectral fitting. The cluster distribution peaks around z = 0.3 and T = 1.5 keV, half of the objects being groups with a temperature below 2 keV. Our L-X-T(z) relation points towards self-similar evolution, but does not exclude other physically plausible models. Assuming that cluster scaling laws follow self-similar evolution, our number density estimates up to z = 1 are compatible with the predictions of the concordance cosmology and with the findings of previous ROSAT surveys. Our well-monitored selection function allowed us to demonstrate that the inclusion of selection effects is essential for the correct determination of the evolution of the L-X-T relation, which may explain the contradictory results from previous studies. Extensive simulations show that extending the survey area to 10 deg(2) has the potential to exclude the non-evolution hypothesis, but those constraints on more refined intracluster medium models will probably be limited by the large intrinsic dispersion of the L-X-T relation, whatever be the sample size. We further demonstrate that increasing the dispersion in the scaling laws increases the number of detectable clusters, hence generating further degeneracy [in addition to sigma(8), Omega(m), L-X-T(z)] in the cosmological interpretation of the cluster number counts. We provide useful empirical formulae for the cluster mass-flux and mass-count rate relations as well as a comparison between the XMM-LSS mass sensitivity and that of forthcoming Sunyaev-Zel'dovich surveys. [less ▲]

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See detailThe XMM-Large scale structure catalogue: X-ray sources and associated optical data. Version I
Pierre, M.; Chiappetti, L.; Pacaud, F. et al

in Monthly Notices of the Royal Astronomical Society (2007), 382(1), 279-290

Following the presentation of the XMM-Large Scale Structure (XMM-LSS) survey X-ray source detection package by Pacaud et al., we provide the source lists for the first surveyed 5.5 deg(2). The catalogues ... [more ▼]

Following the presentation of the XMM-Large Scale Structure (XMM-LSS) survey X-ray source detection package by Pacaud et al., we provide the source lists for the first surveyed 5.5 deg(2). The catalogues pertain to the [0.5-2] and [2-10] keV bands and contain in total 3385 pointlike or extended sources above a detection likelihood of 15 in either band. The agreement with deep log N-log S is excellent. The main parameters considered are position, count rate, source extent with associated likelihood values. A set of additional quantities such as astrometric corrections and fluxes are further calculated while errors on the position and count rate are deduced from simulations. We describe the construction of the band-merged catalogue allowing rapid subsample selection and easy cross-correlation with external multiwavelength catalogues. A small optical Canada-France-Hawaii Telescope Legacy Survey multiband subset of objects are associated with each source along with an X-ray/optical overlay. We make the full X-ray images available in FITS format. The data are available at the Centre de Donnees de Strasbourg and, in a more extended form, at the Milan XMM-LSS survey data base. [less ▲]

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See detailXMM-LSS survey: AGN classifications (Garcet+, 2007)
Garcet, O.; Gandhi, P.; Gosset, Eric ULiege et al

Textual, factual or bibliographical database (2007)

We have used the most up-to-date X-ray catalog (Pierre et al., 2007, Cat. J/MNRAS/382/279) to define a sample of 612 X-ray selected point-like sources which have both a log-likelihood of detection >20 ... [more ▼]

We have used the most up-to-date X-ray catalog (Pierre et al., 2007, Cat. J/MNRAS/382/279) to define a sample of 612 X-ray selected point-like sources which have both a log-likelihood of detection >20 (this roughly corresponds to >3{sigma}) in the [2-10]keV band (see Pacaud et al., 2006MNRAS.372..578P, for full details), and a total number of counts >80 in the [0.5-10]keV band. (1 data file). [less ▲]

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See detailXMM-LSS catalogue. Version I. (Pierre+, 2007)
Pierre, M.; Chiappetti, L.; Pacaud, F. et al

Textual, factual or bibliographical database (2007)

We provide the source list for the first 5.5 surveyed square degrees of the XMM-LSS, with a total of 3385 point-like or extended sources above a detection likelihood of 15 in either 0.5-2 or 2-10keV bands ... [more ▼]

We provide the source list for the first 5.5 surveyed square degrees of the XMM-LSS, with a total of 3385 point-like or extended sources above a detection likelihood of 15 in either 0.5-2 or 2-10keV bands. The table at CDS contains the main parameters, while further parameters and data products (X-ray images and optical thumbnails) are available in the Milan XMM-LSS database site. (1 data file). [less ▲]

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See detail3{sigma} hard sample of XMDS survey (Tajer+, 2007)
Tajer, M.; Polletta, M.; Chiappetti, L. et al

Textual, factual or bibliographical database (2007)

Our goal is to probe the populations of obscured and unobscured AGN investigating their optical-IR and X-ray properties as a function of X-ray flux, luminosity and redshift within a hard X-ray selected ... [more ▼]

Our goal is to probe the populations of obscured and unobscured AGN investigating their optical-IR and X-ray properties as a function of X-ray flux, luminosity and redshift within a hard X-ray selected sample with wide multiwavelength coverage. We selected a sample of 136 X-ray sources detected at a significance of >=3{sigma} in the 2-10keV band (F[SUB]2-10[/SUB]>~10[SUP]-14[/SUP]erg/cm[SUP]2[/SUP]/s) in a ~1deg[SUP]2[/SUP] area in the XMM Medium Deep Survey (XMDS, Cat. ). The XMDS area is covered with optical photometry from the VVDS and CFHTLS surveys and infrared Spitzer data from the SWIRE survey. Based on the X-ray luminosity and X-ray to optical ratio, 132 sources are likely AGN, of which 122 have unambiguous optical - IR identification. The observed optical and IR spectral energy distributions of all identified sources are fitted with AGN/galaxy templates in order to classify them and compute photometric redshifts. X-ray spectral analysis is performed individually for sources with a sufficient number of counts and using a stacking technique for subsamples of sources at different flux levels. Hardness ratios are used to estimate X-ray absorption in individual weak sources. (1 data file). [less ▲]

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See detailStructure detection in the D1 CFHTLS deep field using accurate photometric redshifts: a benchmark
Mazure, A.; Adami, C.; Pierre, M. et al

in Astronomy and Astrophysics (2007), 467(1), 49-62

Aims. We investigate structures in the D1 CFHTLS deep field to test the method that will be applied to generate homogeneous samples of clusters and groups of galaxies in order to constrain the cosmology ... [more ▼]

Aims. We investigate structures in the D1 CFHTLS deep field to test the method that will be applied to generate homogeneous samples of clusters and groups of galaxies in order to constrain the cosmology and detailed physics of groups and clusters. Methods. An adaptive kernel technique was applied to galaxy catalogues. This technique needs none of the usual a-priori assumptions ( luminosity function, density profile, colour of galaxies) made with other methods. Its main drawback ( decrease in efficiency with increasing background) is overcome by the use of narrow slices in photometric redshift space. There are two main concerns in structure detection. One is false detection and the second, the evaluation of the selection function in particular if one wants complete samples. We deal with the first concern using random distributions. For the second, comparison with detailed simulations is foreseen but we used a pragmatic approach by comparing our results to GalICS simulations to check that our detection number is not totally at odds with cosmological simulations. We used the XMM-LSS survey and secured VVDS redshifts up to z similar to 1 to check individual detections. Results. We show that our detection method is basically able to recover 100% of the C1 XMM-LSS X-ray detections ( in the regions in common) in the correct redshift range plus several other candidates. Moreover, when spectroscopic data are available, we confirm our detections, even those without X-ray data. [less ▲]

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See detailObscured and unobscured AGN populations in a hard-X-ray selected sample of the XMDS survey
Tajer, M.; Polletta, M.; Chiappetti, L. et al

in Astronomy and Astrophysics (2007), 467(1), 73-91

Aims. Our goal is to probe the populations of obscured and unobscured AGN investigating their optical-IR and X-ray properties as a function of X-ray flux, luminosity and redshift within a hard X-ray ... [more ▼]

Aims. Our goal is to probe the populations of obscured and unobscured AGN investigating their optical-IR and X-ray properties as a function of X-ray flux, luminosity and redshift within a hard X-ray selected sample with wide multiwavelength coverage. Methods. We selected a sample of 136 X-ray sources detected at a significance of >= 3 sigma in the 2-10 keV band (F2-10 greater than or similar to 10(-1)4 erg cm(-2) s(-1)) in a similar to 1 deg(2) area in the XMM Medium Deep Survey (XMDS). The XMDS area is covered with optical photometry from the VVDS and CFHTLS surveys and infrared Spitzer data from the SWIRE survey. Based on the X-ray luminosity and X-ray to optical ratio, 132 sources are likely AGN, of which 122 have unambiguous optical - IR identification. The observed optical and IR spectral energy distributions of all identified sources are fitted with AGN/galaxy templates in order to classify them and compute photometric redshifts. X-ray spectral analysis is performed individually for sources with a sufficient number of counts and using a stacking technique for subsamples of sources at different flux levels. Hardness ratios are used to estimate X-ray absorption in individual weak sources. Results. 70% of the AGN are fitted by a type 2 AGN or a star forming galaxy template. We group them together in a single class of "optically obscured" AGN. These have "red" optical colors and in about 60% of cases show significant X-ray absorption (N-H > 10(22) cm(-2)). Sources with SEDs typical of type 1 AGN have "blue" optical colors and exhibit X-ray absorption in about 30% of cases. The stacked X-ray spectrum of obscured AGN is flatter than that of type 1 AGN and has an average spectral slope of Gamma = 1.6. The subsample of objects fitted by a star forming galaxy template has an even harder stacked spectrum, with Gamma similar to 1.2-1.3. The obscured fraction is larger at lower fluxes, lower redshifts and lower luminosities. X-ray absorption is less common than "optical" obscuration and its incidence is nearly constant with redshift and luminosity. This implies that at high luminosities X-ray absorption is not necessarily related to optical obscuration. The estimated surface densities of obscured, unobscured AGN and type 2 QSOs are respectively 138, 59 and 35 deg(-2) at F > 10-14 erg cm(-2) s(-1). [less ▲]

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