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تسجيل مستخدم جديدThe XXL survey XIV. AAOmega redshifts for the southern XXL field
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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.
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An X-ray survey with the XMM-Newton telescope, XMM-XXL, has identified hundreds of galaxy groups and clusters in two 25 deg$^2$ fields. Combining spectroscopic and X-ray observations in one field, we determine how the kinetic energy of galaxies scale
s with hot gas temperature and also, by imposing prior constraints on the relative energies of galaxies and dark matter, infer a power-law scaling of total mass with temperature. Our goals are: i) to determine parameters of the scaling between galaxy velocity dispersion and X-ray temperature, $T_{rm 300kpc}$, for the halos hosting XXL-selected clusters, and; ii) to infer the log-mean scaling of total halo mass with temperature, $langle ln M_{200} , | , T, z rangle$. We apply an ensemble velocity likelihood to a sample of $> 1500$ spectroscopic redshifts within $132$ spectroscopically confirmed clusters with redshifts $z < 0.6$ to model, $langle ln sigma_{rm gal},|,T,zrangle$, where $sigma_{rm gal}$ is the velocity dispersion of XXL cluster member galaxies and $T$ is a 300 kpc aperture temperature. To infer total halo mass we use a precise virial relation for massive halos calibrated by N-body simulations along with a single degree of freedom summarizing galaxy velocity bias with respect to dark matter. For the XXL-N cluster sample, we find $sigma_{rm gal} propto T^{0.63pm0.05}$, a slope significantly steeper than the self-similar expectation of $0.5$. Assuming scale-independent galaxy velocity bias, we infer a mean logarithmic mass at a given X-ray temperature and redshift, $langleln (E(z) M_{200}/10^{14},{rm M}_{odot})|T,zrangle=pi+alpha ln(T/T_p )+betaln (E(z)/E(z_p) )$ using pivot values ${rm k}T_{p}=2.2,{rm keV}$ and $z_p=0.25$, with normalization $pi=0.45pm0.24$ and slope $alpha=1.89pm0.15$. We obtain only weak constraints on redshift evolution, $beta=-1.29pm1.14$.
In the currently debated context of using clusters of galaxies as cosmological probes, the need for well-defined cluster samples is critical. The XXL Survey has been specifically designed to provide a well characterised sample of some 500 X-ray detec
ted clusters suitable for cosmological studies. The main goal of present article is to make public and describe the properties of the cluster catalogue in its present state, as well as of associated catalogues as super-clusters and fossil groups. We release a sample containing 365 clusters in total. We give the details of the follow-up observations and explain the procedure adopted to validate the cluster spectroscopic redshifts. Considering the whole XXL cluster sample, we have provided two types of selection, both complete in a particular sense: one based on flux-morphology criteria, and an alternative based on the [0.5-2] keV flux within one arcmin of the cluster centre. We have also provided X-ray temperature measurements for 80$%$ of the clusters having a flux larger than 9$times$10$^{-15}$$rm thinspace erg , s^{-1} , cm^{-2}$. Our cluster sample extends from z$sim$0 to z$sim$1.2, with one cluster at z$sim$2. Clusters were identified through a mean number of six spectroscopically confirmed cluster members. Our updated luminosity function and luminosity-temperature relation are compatible with our previous determinations based on the 100 brightest clusters, but show smaller uncertainties. We also present an enlarged list of super-clusters and a sample of 18 possible fossil groups. This intermediate publication is the last before the final release of the complete XXL cluster catalogue when the ongoing C2 cluster spectroscopic follow-up is complete. It provides a unique inventory of medium-mass clusters over a 50~dd area out to z$sim$1.
Aims: We investigate the properties of the polarised radio population in the central 6.5 deg$^{2}$ of the XXL-South field observed at 2.1 GHz using the Australia Telescope Compact Array (ATCA) in 81 pointings with a synthesised beam of FWHM 5.2. We a
lso investigate the ATCAs susceptibility to polarisation leakage. Methods: We performed a survey of a 5.6 deg$^{2}$ subregion and calculated the number density of polarised sources. We derived the total and polarised spectral indices, in addition to comparing our source positions with those of X-ray-detected clusters. We measured the polarisation of sources in multiple pointings to examine leakage in the ATCA. Results: We find 39 polarised sources, involving 50 polarised source components, above a polarised flux density limit of 0.2 mJy at 1.332 GHz. The number density of polarised source components is comparable with recent surveys, although there is an indication of an excess at $sim1$ mJy. We find that those sources coincident with X-ray clusters are consistent in their properties with regard to the general population. In terms of the ATCA leakage response, we find that ATCA mosaics with beam separation of $lesssim 2/3$ of the primary beam FWHM have off-axis linear polarisation leakage $lesssim 1.4$ % at 1.332 GHz.
Context. Distant galaxy clusters provide an effective laboratory in which to study galaxy evolution in dense environments and at early cosmic times. Aims. We aim to identify distant galaxy clusters as extended X-ray sources coincident with overdensit
ies of characteristically bright galaxies. Methods. We use optical and near-infrared (NIR) data from the Hyper Suprime-Cam (HSC) and VISTA Deep Extragalactic Observations (VIDEO) surveys to identify distant galaxy clusters as overdensities of bright, $z_{phot}geq 0.8$ galaxies associated with extended X-ray sources detected in the ultimate XMM extragalactic survey (XXL). Results. We identify a sample of 35 candidate clusters at $0.80leq zleq 1.93$ from an approximately 4.5 deg$^2$ sky area. This sample includes 15 newly discovered candidate clusters, ten previously detected but unconfirmed clusters, and ten spectroscopically confirmed clusters. Although these clusters host galaxy populations that display a wide variety of quenching levels, they exhibit well-defined relations between quenching, cluster-centric distance, and galaxy luminosity. The brightest cluster galaxies (BCGs) within our sample display colours consistent with a bimodal population composed of an old and red subsample together with a bluer, more diverse subsample. Conclusions. The relation between galaxy masses and quenching seem to be already in place at $zsim 1$, although there is no significant variation of the quenching fraction with the cluster-centric radius. The BCG bimodality might be explained by the presence of a younger stellar component in some BCGs but additional data are needed to confirm this scenario.
Traditionally, galaxy clusters have been expected to retain all the material accreted since their formation epoch. For this reason, their matter content should be representative of the Universe as a whole, and thus their baryon fraction should be clo
se to the Universal baryon fraction. We make use of the sample of the 100 brightest galaxy clusters discovered in the XXL Survey to investigate the fraction of baryons in the form of hot gas and stars in the cluster population. We measure the gas masses of the detected halos and use a mass--temperature relation directly calibrated using weak-lensing measurements for a subset of XXL clusters to estimate the halo mass. We find that the weak-lensing calibrated gas fraction of XXL-100-GC clusters is substantially lower than was found in previous studies using hydrostatic masses. Our best-fit relation between gas fraction and mass reads $f_{rm gas,500}=0.055_{-0.006}^{+0.007}left(M_{rm 500}/10^{14}M_odotright)^{0.21_{-0.10}^{+0.11}}$. The baryon budget of galaxy clusters therefore falls short of the Universal baryon fraction by about a factor of two at $r_{rm 500}$. Our measurements require a hydrostatic bias $1-b=M_X/M_{rm WL}=0.72_{-0.07}^{+0.08}$ to match the gas fraction obtained using lensing and hydrostatic equilibrium. Comparing our gas fraction measurements with the expectations from numerical simulations, our results favour an extreme feedback scheme in which a significant fraction of the baryons are expelled from the cores of halos. This model is, however, in contrast with the thermodynamical properties of observed halos, which might suggest that weak-lensing masses are overestimated. We note that a mass bias $1-b=0.58$ as required to reconcile Planck CMB and cluster counts should translate into an even lower baryon fraction, which poses a major challenge to our current understanding of galaxy clusters. [Abridged]
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