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Register a new userHigh redshift X-ray galaxy clusters. II. The L_X-T relationship revisited
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M. Branchesi
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In this paper we re-visit the observational relation between X-ray luminosity and temperature for high-z galaxy clusters and compare it with the local L_X-T and with theoretical models. To these ends we use a sample of 17 clusters extracted from the Chandra archive supplemented with additional clusters from the literature, either observed by Chandra or XMM-Newton, to form a final sample of 39 high redshift (0.25 < z < 1.3) objects. Different statistical approaches are adopted to analyze the L_X-T relation. The slope of the L_X-T relation of high redshift clusters is steeper than expected from the self-similar model predictions and steeper, even though still compatible within the errors, than the local L_X-T slope. The distant cluster L_X-T relation shows a significant evolution with respect to the local Universe: high-z clusters are more luminous than the local ones by a factor ~2 at any given temperature. The evolution with redshift of the L_X-T relation cannot be described by a single power law nor by the evolution predicted by the self-similar model. We find a strong evolution, similar or stronger than the self-similar model, from z = 0 to z <0.3 followed by a much weaker, if any, evolution at higher redshift. The weaker evolution is compatible with non-gravitational models of structure formation. According to us a statistically significant sample of nearby clusters (z < 0.25) should be observed with the current available X-ray telescopes to completely exclude observational effects due to different generation detectors and to understand this novel result.
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We describe the ensemble X-ray properties of high redshift clusters with emphasis on changes with respect to the local population. Cluster X-ray luminosity evolution is detected in five nearly independent surveys. The relevant issue now is characterizing this evolution. Cluster temperature evolution provides constraints on the dark matter and dark energy content of the universe. These constraints are complementary to and in agreement with those of the cosmic microwave background and supernovae, showing that the present universe is dominated by a dark energy. X-ray images show that most z > 0.75 clusters are not relaxed, hinting that the cluster formation epoch is z ~ 1.
Galaxy clusters are the most recent, gravitationally-bound products of the hierarchical mass accretion over cosmological scales. How the mass is concentrated is predicted to correlate with the total mass in the clusters halo, with systems at higher mass being less concentrated at given redshift and for any given mass, systems with lower concentration are found at higher redshifts. Through a spatial and spectral X-ray analysis, we reconstruct the total mass profile of 47 galaxy clusters observed with Chandra in the redshift range $0.4<z<1.2$, selected to have no major mergers, to investigate the relation between the mass and the dark matter concentration, and the evolution of this relation with redshift. The sample in exam is the largest one investigated so far at $z>0.4$, and is well suited to provide the first constraint on the concentration--mass relation at $z>0.7$ from X-ray analysis. Under the assumptions that the distribution of the X-ray emitting gas is spherically symmetric and in hydrostatic equilibrium, we combine the deprojected gas density and spectral temperature profiles through the hydrostatic equilibrium equation to recover the parameters that describe a NFW total mass distribution. The comparison with results from weak lensing analysis reveals a very good agreement both for masses and concentrations. Uncertainties are however too large to make any robust conclusion on the hydrostatic bias of these systems. The relation is well described by the form $c propto M^B (1+z)^C$, with $B=-0.50 pm 0.20$, $C=0.12 pm 0.61$ (at 68.3% confidence), it is slightly steeper than the one predicted by numerical simulations ($Bsim-0.1$) and does not show any evident redshift evolution. We obtain the first constraints on the properties of the concentration--mass relation at $z > 0.7$ from X-ray data, showing a reasonable good agreement with recent numerical predictions.
We report on the first results from a redshift survey of a flux-limited sample of X-ray clusters selected serendipitously from the ROSAT PSPC data archive. We spectroscopically confirm 15 clusters in the range 0.3 < z < 0.7, to a flux limit of ~ 3.9 x 10^-14 erg s^-1 cm^-2, over a survey area of 17.2 deg^2. The surface density of clusters in our survey is 2.0 (+0.4,-0.3) deg^-2, in good agreement with the number density of cluster candidates detected using algorithms designed to search for very extended sources. The number of clusters detected between 0.3 < z < 0.7 is consistent with a prediction based on a simple extrapolation of the local X-ray cluster luminosity function, which indicates that over this redshift range no significant evolution in the cluster population has taken place. These results are in conflict with recent claims that the number density of X-ray clusters found in deep ROSAT PSPC pointings evolves rapidly beyond z = 0.3.
We present the analysis of deep X-ray observations of 10 massive galaxy clusters at redshifts $1.05 < z < 1.71$, with the primary goal of measuring the metallicity of the intracluster medium (ICM) at intermediate radii, to better constrain models of the metal enrichment of the intergalactic medium. The targets were selected from X-ray and Sunyaev-Zeldovich (SZ) effect surveys, and observed with both the textit{XMM-Newton} and textit{Chandra} satellites. For each cluster, a precise gas mass profile was extracted, from which the value of $r_{500}$ could be estimated. This allows us to define consistent radial ranges over which the metallicity measurements can be compared. In general, the data are of sufficient quality to extract meaningful metallicity measurements in two radial bins, $r<0.3r_{500}$ and $0.3<r/r_{500}<1.0$. For the outer bin, the combined measurement for all ten clusters, $Z/Z_{odot} = 0.21 pm 0.09$, represents a substantial improvement in precision over previous results. This measurement is consistent with, but slightly lower than, the average metallicity of 0.315 Solar measured at intermediate-to-large radii in low-redshift clusters. Combining our new high-redshift data with the previous low-redshift results allows us to place the tightest constraints to date on models of the evolution of cluster metallicity at intermediate radii. Adopting a power law model of the form $Z propto left(1+zright)^gamma$, we measure a slope $gamma = -0.5^{+0.4}_{-0.3}$, consistent with the majority of the enrichment of the ICM having occurred at very early times and before massive clusters formed, but leaving open the possibility that some additional enrichment in these regions may have occurred since a redshift of 2.
In this paper based on ROSAT/PSPC data we investigate the emission measure profiles of a sample of hot clusters of galaxies (kT>3.5keV) in order to explain the differences between observed and theoretically predicted L_X-T relation. Looking at the form of the emission measure profiles as well as their normalizations we find clear indication that indeed the profiles have similar shapes once scaled to the virial radius, however, the normalization of the profiles shows a strong temperature dependence. We introduce a M_gas-T relation with the dependence M_gas propto T^1.94. This relationship explains the observed L_X-T relation and reduces the scatter in the scaled profiles by a factor of 2 when compared to the classical scaling. We interpret this finding as strong indication that the M_gas-T relation in clusters deviates from classical scaling.
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