References of "Georgantopoulos, I"
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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 detailX-ray AGN in the XMM-LSS galaxy clusters: No evidence of AGN suppression
Koulouridis, E.; Plionis, M.; Melnyk, O. et al

in Astronomy and Astrophysics (2014), 567

We present a study of the overdensity of X-ray-selected active galactic nuclei (AGN) in 33 galaxy clusters in the XMM-LSS field (The XMM-Newton Large Scale Structure Survey), up to redshift z = 1.05 and ... [more ▼]

We present a study of the overdensity of X-ray-selected active galactic nuclei (AGN) in 33 galaxy clusters in the XMM-LSS field (The XMM-Newton Large Scale Structure Survey), up to redshift z = 1.05 and further divided into a lower (0.14 ≤ z ≤ 0.35) and a higher redshift (0.43 ≤ z ≤ 1.05) subsample. Previous studies have shown that the presence of X-ray-selected AGN in rich galaxy clusters is suppressed, since their number is significantly lower than what is expected from the high galaxy overdensities in the area. In the current study we have investigated the occurrence of X-ray-selected AGN in low (<Lx, bol> = 2.7 - 1043 erg/s) and moderate (<Lx, bol> = 2.4 × 1044 erg/s) X-ray luminosity galaxy clusters in an attempt to trace back the relation between high-density environments and nuclear activity. Owing to the wide contiguous XMM-LSS survey area, we were able to extend the study to the cluster outskirts. We therefore determined the projected overdensity of X-ray point-like sources around each cluster out to 6r500 radius, within δr500 = 1 annulus, with respect to the field expectations based on the X-ray source log N - log S of the XMM-LSS field. To provide robust statistical results we also conducted a consistent stacking analysis separately for the two z ranges. We investigated whether the observed X-ray overdensities are to be expected thanks to the obvious enhancement of galaxy numbers in the cluster environment by also estimating the corresponding optical galaxy overdensities, and we assessed the possible enhancement or suppression of AGN activity in clusters. We find a positive X-ray projected overdensity in both redshift ranges at the first radial bins, which however has the same amplitude as that of optical galaxies. Therefore, no suppression (or enhancement) of X-ray AGN activity with respect to the field is found, in sharp contrast to previous results based on rich galaxy clusters, implying that the mechanisms responsible for the suppression are not as effective in lower density environments. After a drop to roughly the background level between 2 and 3r500, the X-ray overdensity exhibits a rise at larger radii, significantly greater than the corresponding optical overdensity. The radial distance of this overdensity "bump", corresponding to ∼1.5-3 Mpc, depends on the richness of the clusters, as well as on the overall X-ray overdensity profile. Finally, using the redshift information, photometric or spectroscopic, of the optical counterparts, we derive the spatial overdensity profile of the clusters.We find that the agreement between X-ray and optical overdensities in the first radial bins is also suggested in the 3-dimensional analysis. However, we argue that the X-ray overdensity "bump" at larger radial distance is at least partially a result of flux boosting by gravitational lensing of background quasi-stellar objects, confirming previous results. For high-redshift clusters, the enhancement of X-ray AGN activity in their outskirts appears to be intrinsic. We argue that a spatial analysis is crucial for disentangling irrelevant phenomena affecting the projected analysis, but we are still not able to report statistically significant results on the spatial overdensity of AGN in clusters or their outskirts because we lack the necessary numbers. © ESO 2014. [less ▲]

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See detailThe European Large Area ISO Survey - VI. Discovery of a new hyperluminous infrared galaxy
Morel, Thierry ULiege; Efstathiou, A.; Serjeant, S. et al

in Monthly Notices of the Royal Astronomical Society (2001), 327

We report the discovery of the first hyperluminous infrared galaxy (HyLIG) in the course of the European Large Area ISO Survey (ELAIS). This object has been detected by ISO at 6.7, 15 and 90μm, and is ... [more ▼]

We report the discovery of the first hyperluminous infrared galaxy (HyLIG) in the course of the European Large Area ISO Survey (ELAIS). This object has been detected by ISO at 6.7, 15 and 90μm, and is found to be a broad-line, radio-quiet quasar at a redshift [formmu4]z=1.099. From a detailed multicomponent model fit of the spectral energy distribution, we derive a total IR luminosity L[SUB]IR[/SUB] [formmu5](1-1000μm)~1.0à 10[SUP]13[/SUP]h65-2L[SUB]solar[/SUB] [formmu6](q[SUB]0[/SUB]=0.5), and discuss the possible existence of a starburst contributing to the far-IR output. Observations to date present no evidence for lens magnification. This galaxy is one of the very few HyLIGs with a X-ray detection. On the basis of its soft X-ray properties, we suggest that this broad-line object may be the face-on analogue of narrow-line, Seyfert-like HyLIGs. [less ▲]

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