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See detailXXL Survey XXI. The environment and clustering of X-ray AGN in the XXL-South field
Melnyk, O.; Elyiv, A.; Smolcic, V. et al

in Astronomy and Astrophysics (in press)

This work is part of a series of studies focusing on the environment and the properties of the X-ray selected active galactic nuclei (AGN) population from the XXL survey. The present survey, given its ... [more ▼]

This work is part of a series of studies focusing on the environment and the properties of the X-ray selected active galactic nuclei (AGN) population from the XXL survey. The present survey, given its large area, continuity, extensive multiwavelength coverage, and large-scale structure information, is ideal for this kind of study. Here, we focus on the XXL-South (XXL-S) field. Our main aim is to study the environment of the various types of X-ray selected AGN and investigate its possible role in AGN triggering and evolution. We studied the large-scale (>1 Mpc) environment up to redshift z=1 using the nearest neighbour distance method to compare various pairs of AGN types. We also investigated the small-scale environment (<0.4 Mpc) by calculating the local overdensities of optical galaxies. In addition, we built a catalogue of AGN concentrations with two or more members using the hierarchical clustering method and we correlated them with the X-ray galaxy clusters detected in the XXL survey. It is found that radio detected X-ray sources are more obscured than non-radio ones, though not all radio sources are obscured AGN. We did not find any significant differences in the large-scale clustering between luminous and faint X-ray AGN, or between obscured and unobscured ones, or between radio and non-radio sources. At local scales (<0.4 Mpc), AGN typically reside in overdense regions, compared to non-AGN; however, no differences were found between the various types of AGN. A majority of AGN concentrations with two or more members are found in the neighbourhood of X-ray galaxy clusters within <25-45 Mpc. Our results suggest that X-ray AGN are typically located in supercluster filaments, but they are also found in over- and underdense regions. [less ▲]

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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 detailGRB 061006: optical afterglow.
Malesani, D.; Stella, L.; D'Avanzo, P. et al

in GRB Coordinates Network (2006), 5718

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See detailPhotometric monitoring of the doubly imaged quasar UM 673: possible evidence for chromatic microlensing
Nakos, Theodoros; Courbin, F.; Poels, Joël ULiege et al

in Astronomy and Astrophysics (2005), 441

We present the results of two-band CCD photometric monitoring of the gravitationally lensed quasar Q 0142-100 (UM 673). The data, obtained at ESO-La Silla with the 1.54 m Danish telescope in the Gunn i ... [more ▼]

We present the results of two-band CCD photometric monitoring of the gravitationally lensed quasar Q 0142-100 (UM 673). The data, obtained at ESO-La Silla with the 1.54 m Danish telescope in the Gunn i-band (October 1998-September 1999) and in the Johnson V-band (October 1998 to December 2001), were analyzed using three different photometric methods. The light-curves obtained with all methods show variations, with a peak-to-peak amplitude of 0.14 mag in V. Although it was not possible to measure the time delay between the two lensed QSO images, the brighter component displays possible evidence for microlensing: it becomes bluer as it gets brighter, as expected under the assumption of differential magnification of a quasar accretion disk. [less ▲]

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See detailAn optical time delay for the double gravitational lens system FBQ 0951+2635
Jakobsson, P.; Hjorth, J.; Burud, I. et al

in Astronomy and Astrophysics (2005), 431(1), 103-109

We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay ... [more ▼]

We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay of Deltatau = 16 +/- 2 days (1sigma) is determined from the light curves. New constraints on the lensing geometry are provided by the position and ellipticity of the lensing galaxy. For a (Omega(m), Omega(Lambda)) = (0.3, 0.7) cosmology, the time delay yields a Hubble parameter of H-0 = 60(-7)(+9) (random, 1sigma) +/-2 (systematic) km s(-1) Mpc(-1) for a singular isothermal ellipsoid model and H-0 = 63(-7)(+9) (random, 1sigma) +/-1 (systematic) km s(-1) Mpc(-1) for a constant mass-to-light ratio model. In both models, the errors are mainly due to the time-delay uncertainties. Non-parametric models yield H-0 = 64(-7)(+9) (random, 1sigma) +/- 14 (systematic) km s(-1) Mpc(-1). [less ▲]

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See detailAn optical time-delay for the lensed BAL quasar HE 2149-2745
Burud, I.; Courbin, F.; Magain, Pierre ULiege et al

in Astronomy and Astrophysics (2002), 383(1), 71-81

We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149-2745. The data, obtained with the 1.5 m Danish Telescope (ESO-La Silla) between October 1998 and December 2000 ... [more ▼]

We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149-2745. The data, obtained with the 1.5 m Danish Telescope (ESO-La Silla) between October 1998 and December 2000, are the first from a long-term project aimed at monitoring selected lensed quasars in the Southern Hemisphere. A time delay of 103+/-12 days is determined from the light curves. In addition, VLT/FORS1 spectra of HE 2149 2745 are deconvolved in order to obtain the spectrum of the faint lensing galaxy, free of any contamination by the bright nearby two quasar images. By cross-correlating the spectrum with galaxy-templates we obtain a tentative redshift estimate of z = 0.495+/-0:01. Adopting this redshift, a Omega = 0.3, Lambda = 0.7 cosmology, and a chosen analytical lens model, our time-delay measurement yields a Hubble constant of H-0 = 66+/-8 km s(-1) Mpc(-1) (1sigma error) with an estimated systematic error of +/-3 km s(-1) Mpc(-1). Using non-parametric models yields H-0 = 65+/-8 km s(-1) Mpc(-1) (1sigma error) and confirms that the lens exhibits a very dense/concentrated mass profile. Finally, we note, as in other cases, that the flux ratio between the two quasar components is wavelength dependent. While the flux ratio in the broad emission lines-equal to 3.7-remains constant with wavelength, the continuum of the brighter component is bluer. Although the data do not rule out extinction of one quasar image relative to the other as a possible explanation, the effect could also be produced by differential microlensing by stars in the lensing galaxy. [less ▲]

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See detailDeconvolving Spectra: Near-IR Spectroscopy of the Lens and Source in HE 1104-1805
Courbin, F.; Lidman, C.; Meylan, G. et al

in Brainerd, T. G.; Kochanek, C. S. (Eds.) Gravitational Lensing: Recent Progress and Future Go (2001, January 01)

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See detailLensed quasars: a matter of resolution
Courbin, F.; Lidman, C.; Burud, I. et al

in The Messenger (2000), 101

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See detailExploring the gravitationally lensed system HE 1104-1805: near-IR spectroscopy
Courbin, F.; Lidman, C.; Meylan, G. et al

in Astronomy and Astrophysics (2000), 360

A new technique for the spatial deconvolution of spectra is applied to near-IR (0.95-2.50 mum) NTT/SOFI spectra of the lensed, radio-quiet quasar HE 1104-1805. The continuum of the lensing galaxy is ... [more ▼]

A new technique for the spatial deconvolution of spectra is applied to near-IR (0.95-2.50 mum) NTT/SOFI spectra of the lensed, radio-quiet quasar HE 1104-1805. The continuum of the lensing galaxy is revealed between 1.5 mum and 2.5 mum. Although the spectrum does not show strong emission features, it is used in combination with previous optical and IR photometry to infer a plausible redshift in the range 0.8 < z < 1.2. Modeling of the system shows that the lens is complex, probably composed of the red galaxy seen between the quasar images and a more extended component associated with a galaxy cluster with fairly low velocity dispersion (~ 575 km s[SUP]-1[/SUP]). Unless more constrains can be put on the mass distribution of the cluster, e.g. from deep X-ray observations, HE 1104-1805 will not be a good system to determine H[SUB]0[/SUB]. We stress that multiply imaged quasars with known time delays may prove more useful as tools for detecting dark mass in distant lenses than for determining cosmological parameters. The spectra of the two lensed images of the source are of great interest. They show no trace of reddening at the redshift of the lens nor at the redshift of the source. This supports the hypothesis of an elliptical lens. Additionally, the difference between the spectrum of the brightest component and that of a scaled version of the faintest component is a featureless continuum. Broad and narrow emission lines, including the FeII features, are perfectly subtracted. The very good quality of our spectrum makes it possible to fit precisely the optical Fe II feature, taking into account the underlying continuum over a wide wavelength range. HE 1104-1805 can be classified as a weak Fe II emitter. Finally, the slope of the continuum in the brightest image is steeper than the continuum in the faintest image and supports the finding by Wisotzki et al. (1993) that the brightest image is microlensed. This is particularly interesting in view of the new source reconstruction methods from multiwavelength photometric monitoring. While HE 1104- 1805 does not seem the best target for determining cosmological parameters, it is probably the second most interesting object after Q 2237+0305 (the Einstein cross), in terms of microlensing. Based on observations collected with the ESO New Technology Telescope (program 61.B-0413) [less ▲]

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See detailDeconvolving spectra of lensing galaxies, QSO hosts, and more ...
Courbin, F.; Magain, Pierre ULiege; Sohy, Sandrine ULiege et al

in The Messenger (1999), 97

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See detailBIMA and Keck Imaging of the Radio Ring PKS 1830-211
Frye, B. L.; Courbin, F.; Broadhurst, T. J. et al

in Carilli, C. L.; Radford, S. J. E.; Menten, K. M. (Eds.) et al Highly Redshifted Radio Lines (1999)

We discuss BIMA (Berkeley Illinois Maryland Association) data and present new h igh quality optical and near-IR Keck images of the bright radio ring PKS 1830-211. Applying a powerful new deconvolution ... [more ▼]

We discuss BIMA (Berkeley Illinois Maryland Association) data and present new h igh quality optical and near-IR Keck images of the bright radio ring PKS 1830-211. Applying a powerful new deconvolution algorithm we have been able to identify both images of the radio source. In addition we recover an extended source in the optical, consistent with the expected location of the lensing galaxy. The source counterparts are very red, I-K ~7 suggesting strong Galactic absorption with additional absorption by the lensing galaxy at z = 0.885, and consistent with the detection of high redshift molecules in the lens. [less ▲]

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See detailDeep imaging of AXJ2019+112: The luminosity of a ``Dark Cluster''
Benitez, N.; Broadhurst, T.; Rosati, P. et al

in Paul, J.; Montmerle, T.; Aubourg, E. (Eds.) 19th Texas Symposium on Relativistic Astrophysics and Cosmology (1998, December 01)

We detect a distant cluster of galaxies at z ~1 centered on the QSO lens and luminous X-ray source AXJ2019+112 (Hattori et al 1997). The mass-to-light ratio within an aperture of 0.4 h ^{-1}Mpc determined ... [more ▼]

We detect a distant cluster of galaxies at z ~1 centered on the QSO lens and luminous X-ray source AXJ2019+112 (Hattori et al 1997). The mass-to-light ratio within an aperture of 0.4 h ^{-1}Mpc determined using the X-ray temperature is M_x / L_V = 190^{+95}_{-66}h(M/L_V)[SUB]sun[/SUB]. The strong lens model yields a compatible value, M/L_V = 315^{+80}_{-80}h(M/L_V)[SUB]sun[/SUB], whereas an independent weak lensing analysis sets an upper limit of M/L_V < 440 h(M/L_V)[SUB]sun[/SUB]. This confirms that AXJ2019+112 has a M/L ratio similar to that of z < 1 massive clusters. [less ▲]

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See detailHigh-Resolution Optical and Near-Infrared Imaging of the Quadruple Quasar RX J0911.4+0551
Burud, I.; Courbin, F.; Lidman, C. et al

in Astrophysical Journal (1998), 501

We report the detection of four images in the recently discovered lensed QSO RX J0911.4+0551. With a maximum angular separation of 3."1, it is the quadruply imaged QSO with the widest known angular ... [more ▼]

We report the detection of four images in the recently discovered lensed QSO RX J0911.4+0551. With a maximum angular separation of 3."1, it is the quadruply imaged QSO with the widest known angular separation. Raw and deconvolved data reveal an elongated lens galaxy. The observed reddening in at least two of the four QSO images suggests differential extinction by this lensing galaxy. We show that both an ellipticity of the galaxy ( epsilon _{{min}}=0.075 ) and an external shear ( gamma _{{min}}=0.15 ) from a nearby mass have to be included in the lensing potential in order to reproduce the complex geometry observed in RX J0911.4+0551. A possible galaxy cluster is detected about 38" from RX J0911.4+0551 and could contribute to the X-ray emission observed by ROSAT in this field. The color of these galaxies indicates a plausible redshift in the range of 0.6-0.8. [less ▲]

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See detailImage Deconvolution of the Radio Ring PKS 1830-211
Courbin, F.; Lidman, C.; Frye, B. L. et al

in Astrophysical Journal (1998), 499

New high-quality Keck and ESO images of PKS 1830-211 are presented. By applying a powerful new deconvolution algorithm to these optical and infrared data, both images of the flat spectrum core of the ... [more ▼]

New high-quality Keck and ESO images of PKS 1830-211 are presented. By applying a powerful new deconvolution algorithm to these optical and infrared data, both images of the flat spectrum core of the radio source have been identified. An extended source is also detected in the optical images which is consistent with the expected location of the lensing galaxy. The source counterparts are very red at I-K~7 , which suggests strong Galactic absorption with additional absorption by the lensing galaxy at z=0.885 and is consistent with the detection of high-redshift molecules in the lens. [less ▲]

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See detailRX J0911.4+0551: a complex quadruply imaged gravitationally lensed QSO.
Burud, I.; Courbin, F.; Lidman, C. et al

in The Messenger (1998), 92

The authors present their first observations of RX J0911.4+0551 at the 2.2-m ESO/MPI IRAC 2b in K-band which made them suspect that the QSO might be quadruple. This was confirmed on the optical data from ... [more ▼]

The authors present their first observations of RX J0911.4+0551 at the 2.2-m ESO/MPI IRAC 2b in K-band which made them suspect that the QSO might be quadruple. This was confirmed on the optical data from the 2.56-m Nordic Optical Telescope, and on the NTT/SOFI data of the object. Careful deconvolution of the data allows to clearly resolve the object into four QSO components and a lensing galaxy. [less ▲]

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See detailDetection of the lensing galaxy in HE 1104-1805
Courbin, F.; Lidman, C.; Magain, Pierre ULiege

in Astronomy and Astrophysics (1998), 330

We report on deep IR imaging of the double quasar HE 1104-1805. A new image deconvolution technique has been applied to the data in order to optimally combine the numerous frames obtained. The resulting J ... [more ▼]

We report on deep IR imaging of the double quasar HE 1104-1805. A new image deconvolution technique has been applied to the data in order to optimally combine the numerous frames obtained. The resulting J and K' images allow us to detect and study the lensing galaxy between the two lensed QSO images. The near infrared images not only confirm the lensed nature of this double quasar, but also support the previous redshift estimate of z=1.66 for the lensing galaxy. No obvious overdensity of galaxies is detected in the immediate region surrounding the lens, down to limiting magnitudes of J=22 and K=20. The geometry of the system, together with the time delays expected for this lensed quasar, make HE 1104-1805 a remarkable target for future photometric monitoring programs, for the study of microlensing and for the determination of the cosmological parameters in the IR and optical domains. Based on observations obtained at ESO, La Silla, Chile [less ▲]

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