Cl 1205+44, a fossil group at z = 0.59

This is a report of Chandra, XMM-Newton, HST and ARC observations of an extended X-ray source at z = 0.59. The apparent member galaxies range from spiral to elliptical and are all relatively red (i'-Ks about 3). We interpret this object to be a fossil group based on the difference between the brightness of the first and second brightest cluster members in the i'-band, and because the rest-frame bolometric X-ray luminosity is about 9.2x10^43 h70^-2 erg s^-1. This makes Cl 1205+44 the highest redshift fossil group yet reported. The system also contains a central double-lobed radio galaxy which appears to be growing via the accretion of smaller galaxies. We discuss the formation and evolution of fossil groups in light of the high redshift of Cl 1205+44.Comment: 21 pages, 13 figures, minor corrections to match published ApJ versio

The Representative XMM-Newton Cluster Structure Survey (REXCESS) of an X-ray Luminosity Selected Galaxy Cluster Sample

The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure, and of the scaling relations between observables and cluster mass. To improve on this situation we have started an XMM-Newton Large Programme for the in-depth study of a representative sample of 33 galaxy clusters, selected in the redshift range z=0.055 to 0.183 from the REFLEX Cluster Survey, having X-ray luminosities above 0.4 X 10^44 h_70^-2 erg s^-1 in the 0.1 - 2.4 keV band. This paper introduces the sample, compiles properties of the clusters, and provides detailed information on the sample selection function. We describe the selection of a nearby galaxy cluster sample that makes optimal use of the XMM-Newton field-of-view, and provides nearly homogeneous X-ray luminosity coverage for the full range from poor clusters to the most massive objects in the Universe. For the clusters in the sample, X-ray fluxes are derived and compared to the previously obtained fluxes from the ROSAT All-Sky Survey. We find that the fluxes and the flux errors have been reliably determined in the ROSAT All-Sky Survey analysis used for the REFLEX Survey. We use the sample selection function documented in detail in this paper to determine the X-ray luminosity function, and compare it with the luminosity function of the entire REFLEX sample. We also discuss morphological peculiarities of some of the sample members. The sample and some of the background data given in this introductory paper will be important for the application of these data in the detailed studies of cluster structure, to appear in forthcoming publications.Comment: 17 pages, 17 figures; to appear in A&A. A pdf version with full-quality figures can be found at ftp://ftp.xray.mpe.mpg.de/people/gwp/xmmlp/xmmlp.pd

The XMM Cluster Survey: New evidence for the 3.5-keV feature in clusters is inconsistent with a dark matter origin

There have been several reports of a detection of an unexplained excess of X-ray emission at $\simeq$3.5 keV in astrophysical systems. One interpretation of this excess is the decay of sterile neutrino dark matter. The most influential study to date analysed 73 clusters observed by the XMM-Newton satellite. We explore evidence for a â 3.5-keV excess in the XMM-PN spectra of 117 redMaPPer galaxy clusters (0.1 < z < 0.6). In our analysis of individual spectra, we identify three systems with an excess of flux at $\simeq$3.5 keV. In one case (XCS J0003.3+0204), this excess may result from a discrete emission line. None of these systems are the most dark matter dominated in our sample. We group the remaining 114 clusters into four temperature (TX) bins to search for an increase in â 3.5-keV flux excess with TX-a reliable tracer of halo mass. However, we do not find evidence of a significant excess in flux at â 3.5 keV in any TX bins. To maximize sensitivity to a potentially weak dark matter decay feature at â 3.5 keV, we jointly fit 114 clusters. Again, no significant excess is found at â 3.5 keV. We estimate the upper limit of an undetected emission line at â 3.5 keV to be 2.41 × 10-6 photons cm-2 s-1, corresponding to a mixing angle of sin 2(2θ) = 4.4 × 10-11, lower than previous estimates from cluster studies. We conclude that a flux excess at â 3.5 keV is not a ubiquitous feature in clusters and therefore unlikely to originate from sterile neutrino dark matter decay. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society

Cl1205+44: an atypic cluster/group of galaxies observed with XMM-Newton and Chandra.

We selected a number of distant cluster candidates from ROSAT PSPC data in the SHARC survey; part of these were observed with optical and infrared imaging through various filters. Optical colours indicate that galaxies in Cl1205+44 are very red and suggest a redshift greater than 1. However, optical redshifts of galaxies obtained very recently by J. Mulchaey in this area show a concentration of galaxies around z=0.33. Our recent observations of this object with XMM-Newton and Chandra confirm the presence of a faint extended X-ray source; if the redshift is fixed to 0.33, the X-ray gas has a temperature of 2.7 keV, and a bolometric luminosity of 2.4 10**43 ergs. Cl1205+44 seems therefore to be a poor structure at redshift 0.33. Several points make it, however, remarkable. Galaxies are very red for a z=0.33 structure. There is only a very low number of galaxies in the X-ray emission area, consistently with what would happen with a poor group or a fossil group of galaxies. However, the (Lx/Tx) value for Cl1205+44 does not follow the relation for nearby groups or clusters (Jones L.R. et al. 2003), while it falls on the Lx/Tx relation for intermediate redshift (z=0.3) rich clusters (Novicki et al. 2002), without being rich enough to be such a rich structure. This possibly suggests an evolution of the Lx-Tx relation for both groups and clusters of galaxies. We present here an analysis of the main X-ray properties of Cl1205+44 and explain why this structure is possibly filling the gap between groups and clusters of galaxies

Probing structure formation physics with the evolution of galaxy cluster properties

XMM-Newton and Chandra observations show that the dark-matter profile of local galaxy clusters is universal, with a central cusp, as predicted by numerical simulations. In contrast, the physics governing the baryonic component remains far from being understood: the gas properties of local clusters do scale self-similarly down to low masses (around 2 keV), but the scaling laws differ from the simplest expectations. It appears that the gas history depends not only on gravitational effects but also on the interplay between cooling and various galaxy feedback mechanisms, none of which are well understood. Recent evolution studies confirm that clusters follow scaling laws up to high redshifts, but the amount of evolution remains uncertain. We were awarded a XMM-Newton Large Programme in AO4 to assess the evolution of the structural and scaling properties of an unbiased sample of 23 clusters at a redshift of 0.5, covering a large mass range (2.5 to 12 keV). In this contribution we describe the initial results of the full sample and compare the cluster properties to local samples. We acknowledge support from NASA grant NNG0-5GL94G and NASA Contract NAS8-39073

Optical and X-ray observations of the merging cluster AS1063

We present the first in-depth analysis of the massive cluster AS1063. This is one of the hottest X-ray clusters discovered to date and is undergoing a major merging event. The average temperature of the hot intracluster medium has been measured, using Chandra/ACIS-I, and found to be >11.5 keV. Optical spectroscopy, from GMOS-S, has provided a mean redshift of 0.3461 and a large velocity dispersion of 1840+230 – 150 km s–1. Both the large velocity dispersion and high X-ray temperature suggest a very massive cluster (M 200 > 2.5 × 1015 M ☉) and/or a merger system. The merger model is supported by a small offset between the galaxy density and the peak of the X-ray emission, the presence of offset and twisted X-ray isophotes, and a non-Gaussian galaxy velocity distribution. We also report that the velocity distribution is better represented by the velocity dispersion produced during a merger than by the velocity distribution of a relaxed cluster. Moreover, we find that two non-concentric beta models are a better description for the distribution of the cluster gas than a single beta model. Therefore, we propose that a recent merger event close to the plane of the sky is responsible for the observed properties of the cluster. In addition, optical imaging, from SuSI2 on the New Technology Telescope and GMOS-S at Gemini, has also uncovered the presence of several gravitational arcs that have been used to further constrain the mass and dynamics of the cluster

The representative XMM-Newton cluster structure survey (REXCESS) of an X-ray luminosity selected galaxy cluster sample

Context. The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure, and of the scaling relations between observables and cluster mass. Aims. To improve on this situation we have started an XMM-Newton Large Programme for the in-depth study of a representative sample of 33 galaxy clusters, selected in the redshift range z = 0.055 to 0.183 from the REFLEX Cluster Survey, having X-ray luminosities above 0.4 x 10(44) h(70)(-2) erg s(-1) in the 0.1-2.4 keV band. This paper introduces the sample, compiles properties of the clusters, and provides detailed information on the sample selection function. Methods. We describe the selection of a nearby galaxy cluster sample that makes optimal use of the XMM-Newton field-of-view, and provides nearly homogeneous X-ray luminosity coverage for the full range from poor clusters to the most massive objects in the Universe. Results. For the clusters in the sample, X-ray fluxes are derived and compared to the previously obtained fluxes from the ROSAT All-Sky Survey. We find that the fluxes and the flux errors have been reliably determined in the ROSAT All-Sky Survey analysis used for the REFLEX Survey. We use the sample selection function documented in detail in this paper to determine the X-ray luminosity function, and compare it with the luminosity function of the entire REFLEX sample. We also discuss morphological peculiarities of some of the sample members. Conclusions. The sample and some of the background data given in this introductory paper will be important for the application of these data in the detailed studies of cluster structure, to appear in forthcoming publications

The XMM Cluster Survey: new evidence for the 3.5-keV feature in clusters is inconsistent with a dark matter origin

There have been several reports of a detection of an unexplained excess of X-ray emission at ?3.5 keV in astrophysical systems. One interpretation of this excess is the decay of sterile neutrino dark matter. The most influential study to date analysed 73 clusters observed by the XMM–Newton satellite. We explore evidence for a ?3.5-keV excess in the XMM-PN spectra of 117 redMaPPer galaxy clusters (0.1 < z < 0.6). In our analysis of individual spectra, we identify three systems with an excess of flux at ?3.5 keV. In one case (XCS J0003.3+0204), this excess may result from a discrete emission line. None of these systems are the most dark matter dominated in our sample. We group the remaining 114 clusters into four temperature (TX) bins to search for an increase in ?3.5-keV flux excess with TX – a reliable tracer of halo mass. However, we do not find evidence of a significant excess in flux at ?3.5 keV in any TX bins. To maximize sensitivity to a potentially weak dark matter decay feature at ?3.5 keV, we jointly fit 114 clusters. Again, no significant excess is found at ?3.5 keV. We estimate the upper limit of an undetected emission line at ?3.5 keV to be 2.41 × 10-6 photons cm-2 s-1, corresponding to a mixing angle of sin?2(2?) = 4.4 × 10-11, lower than previous estimates from cluster studies. We conclude that a flux excess at ?3.5 keV is not a ubiquitous feature in clusters and therefore unlikely to originate from sterile neutrino dark matter decay

The representative XMM-Newton cluster structure survery (REXCESS) of an X-ray luminosity selected galaxy cluster sample

The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure, and of the scaling relations between observables and cluster mass. To improve on this situation we have started an XMM-Newton Large Programme for the in-depth study of a representative sample of 33 galaxy clusters, selected in the redshift range z=0.055 to 0.183 from the REFLEX Cluster Survey, having X-ray luminosities above 0.4 X 10^44 h_70^-2 erg s^-1 in the 0.1 - 2.4 keV band. This paper introduces the sample, compiles properties of the clusters, and provides detailed information on the sample selection function. We describe the selection of a nearby galaxy cluster sample that makes optimal use of the XMM-Newton field-of-view, and provides nearly homogeneous X-ray luminosity coverage for the full range from poor clusters to the most massive objects in the Universe. For the clusters in the sample, X-ray fluxes are derived and compared to the previously obtained fluxes from the ROSAT All-Sky Survey. We find that the fluxes and the flux errors have been reliably determined in the ROSAT All-Sky Survey analysis used for the REFLEX Survey. We use the sample selection function documented in detail in this paper to determine the X-ray luminosity function, and compare it with the luminosity function of the entire REFLEX sample. We also discuss morphological peculiarities of some of the sample members. The sample and some of the background data given in this introductory paper will be important for the application of these data in the detailed studies of cluster structure, to appear in forthcoming publications.Comment: 17 pages, 17 figures; to appear in A&A. A pdf version with full-quality figures can be found at ftp://ftp.xray.mpe.mpg.de/people/gwp/xmmlp/xmmlp.pd