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Register a new userNew constraints on dark energy from the observed growth of the most X-ray luminous galaxy clusters
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A. Mantz
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We present constraints on the mean matter density, Omega_m, the normalization of the density fluctuation power spectrum, sigma_8, and the dark-energy equation-of-state parameter, w, obtained from measurements of the X-ray luminosity function of the largest known galaxy clusters at redshifts z<0.7, as compiled in the Massive Cluster Survey (MACS) and the local BCS and REFLEX galaxy cluster samples. Our analysis employs an observed mass-luminosity relation, calibrated by hydrodynamical simulations, including corrections for non-thermal pressure support and accounting for the presence of intrinsic scatter. Conservative allowances for all known systematic uncertainties are included, as are standard priors on the Hubble constant and mean baryon density. We find Omega_m=0.28 +0.11 -0.07 and sigma_8=0.78 +0.11 -0.13 for a spatially flat, cosmological-constant model, and Omega_m=0.24 +0.15 -0.07, sigma_8=0.85 +0.13 -0.20 and w=-1.4 +0.4 -0.7 for a flat, constant-w model. Future work improving our understanding of redshift evolution and observational biases affecting the mass--X-ray luminosity relation have the potential to significantly tighten these constraints. Our results are consistent with those from recent analyses of type Ia supernovae, cosmic microwave background anisotropies, the X-ray gas mass fraction of relaxed galaxy clusters, baryon acoustic oscillations and cosmic shear. Combining the new X-ray luminosity function data with current supernova, cosmic microwave background and cluster gas fraction data yields the improved constraints Omega_m=0.269 +- 0.016, sigma_8=0.82 +- 0.03 and w=-1.02 +- 0.06. (Abridged)
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We present the first three galaxy clusters of a larger sample of the most X-ray luminous galaxy clusters selected from the ROSAT Bright Survey. This project, which is a systematic search for strong lensing, aims at arc statistics, mass determinations and studies of distant lensed galaxies. The three galaxy clusters presented here have been observed with the Wide Field Imager at the ESO2.2m in the R- and V-band. The images show lensing features like distinct distorted galaxies and arcs. Mass distributions of the lensing galaxy clusters and photometric properties of some arc candidates are presented. In addition we report the discovery of three giant arcs.
We present constraints on the mean matter density, Omega_m, dark energy density, Omega_de, and the dark energy equation of state parameter, w, using Chandra measurements of the X-ray gas mass fraction (fgas) in 42 hot (kT>5keV), X-ray luminous, dynamically relaxed galaxy clusters spanning the redshift range 0.05<z<1.1. Using only the fgas data for the 6 lowest redshift clusters at z<0.15, for which dark energy has a negligible effect on the measurements, we measure Omega_m=0.28+-0.06 (68% confidence, using standard priors on the Hubble Constant, H_0, and mean baryon density, Omega_bh^2). Analyzing the data for all 42 clusters, employing only weak priors on H_0 and Omega_bh^2, we obtain a similar result on Omega_m and detect the effects of dark energy on the distances to the clusters at ~99.99% confidence, with Omega_de=0.86+-0.21 for a non-flat LCDM model. The detection of dark energy is comparable in significance to recent SNIa studies and represents strong, independent evidence for cosmic acceleration. Systematic scatter remains undetected in the fgas data, despite a weighted mean statistical scatter in the distance measurements of only ~5%. For a flat cosmology with constant w, we measure Omega_m=0.28+-0.06 and w=-1.14+-0.31. Combining the fgas data with independent constraints from CMB and SNIa studies removes the need for priors on Omega_bh^2 and H_0 and leads to tighter constraints: Omega_m=0.253+-0.021 and w=-0.98+-0.07 for the same constant-w model. More general analyses in which we relax the assumption of flatness and/or allow evolution in w remain consistent with the cosmological constant paradigm. Our analysis includes conservative allowances for systematic uncertainties. The small systematic scatter and tight constraints bode well for future dark energy studies using the fgas method. (Abridged)
(Abridged) This is the second in a series of papers in which we derive simultaneous constraints on cosmology and X-ray scaling relations using observations of massive, X-ray flux-selected galaxy clusters. The data set consists of 238 clusters drawn from the ROSAT All-Sky Survey with 0.1-2.4 keV luminosities >2.5e44 erg/second, and incorporates extensive follow-up observations using the Chandra X-ray Observatory. Our analysis accounts self-consistently for all selection effects, covariances and systematic uncertainties. Here we describe the reduction of the follow-up X-ray observations, present results on the cluster scaling relations, and discuss their implications. Our constraints on the luminosity-mass and temperature-mass relations, measured within r_500, lead to three important results. First, the data support the conclusion that excess heating of the intracluster medium has altered its thermodynamic state from that expected in a simple, gravitationally dominated system; however, this excess heating is primarily limited to the central regions of clusters (r<0.15r_500). Second, the intrinsic scatter in the center-excised luminosity-mass relation is remarkably small, being undetected at the <10% level in current data; for the hot, massive clusters under investigation, this scatter is smaller than in either the temperature-mass or Y_X-mass relations (10-15%). Third, the evolution with redshift of the scaling relations is consistent with the predictions of simple, self-similar models of gravitational collapse, indicating that the mechanism responsible for heating the central regions of clusters was in operation before redshift 0.5 (the limit of our data) and that its effects on global cluster properties have not evolved strongly since then.
We constrain cold dark energy of negligible sound speed using galaxy cluster abundance observations. In contrast to standard quasi-homogeneous dark energy, negligible sound speed implies clustering of the dark energy fluid at all scales, allowing us to measure the effects of dark energy perturbations at cluster scales. We compare those models and set the stage for using non-linear information from semi-analytical modelling in cluster growth data analyses. For this, we recalibrate the halo mass function with non-linear characteristic quantities, the spherical collapse threshold and virial overdensity, that account for model and redshift dependent behaviours, as well as an additional mass contribution for cold dark energy. We present the first constraints from this cold dark matter plus cold dark energy mass function using our cluster abundance likelihood, which self-consistently accounts for selection effects, covariances and systematic uncertainties. We combine cluster growth data with CMB, SNe Ia and BAO data, and find a shift between cold versus quasi-homogeneous dark energy of up to $1sigma$. We make a Fisher matrix forecast of constraints attainable with cluster growth data from the on-going Dark Energy Survey (DES). For DES, we predict $sim$50$%$ tighter constraints on $left(Omega_mathrm{m},w right)$ for cold dark energy versus $w$CDM models, with the same free parameters. Overall, we show that cluster abundance analyses are sensitive to cold dark energy, an alternative, viable model that should be routinely investigated alongside the standard dark energy scenario.
We show how to improve constraints on Omega_m, sigma_8, and the dark-energy equation-of-state parameter, w, obtained by Mantz et al. (2008) from measurements of the X-ray luminosity function of galaxy clusters, namely MACS, the local BCS and the REFLEX galaxy cluster samples with luminosities L> 3 times 10^{44} erg/s in the 0.1--2.4 keV band. To this aim, we use Tinker et al. (2008) mass function instead of Jenkins et al. (2001) and the M-L relationship obtained from Del Popolo (2002) and Del Popolo et al. (2005). Using the same methods and priors of Mantz et al. (2008), we find, for a Lambda$CDM universe, Omega_m=0.28^{+0.05}_{-0.04} and sigma_8=0.78^{+0.04}_{-0.05}$ while the result of Mantz et al. (2008) gives less tight constraints $Omega_m=0.28^{+0.11}_{-0.07}$ and sigma_8=0.78^{+0.11}_{-0.13}. In the case of a wCDM model, we find Omega_m=0.27^{+0.07}_{-0.06}, $sigma_8=0.81^{+0.05}_{-0.06}$ and $w=-1.3^{+0.3}_{-0.4}$, while in Mantz et al. (2008) they are again less tight Omega_m=0.24^{+0.15}_{-0.07}, sigma_8=0.85^{+0.13}_{-0.20} and w=-1.4^{+0.4}_{-0.7}. Combining the XLF analysis with the f_{gas}+CMB+SNIa data set results in the constraint Omega_m=0.269 pm 0.012, sigma_8=0.81 pm 0.021 and w=-1.02 pm 0.04, to be compared with Mantz et al. (2008), Omega_m=0.269 pm 0.016, sigma_8=0.82 pm 0.03 and w=-1.02 pm 0.06. The tightness of the last constraints obtained by Mantz et al. (2008), are fundamentally due to the tightness of the $f_{gas}$+CMB+SNIa constraints and not to their XLF analysis. Our findings, consistent with w=-1, lend additional support to the cosmological-constant model.
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