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Register a new userX-ray mass proxies from hydrodynamic simulations of galaxy clusters (paper I)
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We present a detailed study of scaling relations between total cluster mass and three mass proxies based on X-ray observables: temperature of the intra-cluster medium, gas mass and the product of the two, Y_X. Our analysis is based on two sets of high-resolution hydrodynamical simulations performed with the TreePM-SPH GADGET code. The first set includes about 140 clusters with masses above 5x10^13 M_sun/h (30 having mass above 10^15 M_sun/h), that have been simulated with (i) non-radiative physics and including (ii) cooling, star formation, chemical enrichment and the effect of supernova feedback triggering galactic ejecta. This large statistics is used to quantify the robustness of the scaling relations, to determine their redshift evolution and to calibrate their intrinsic scatter and its distribution. We use a smaller set of clusters including 18 halos with masses above 5x10^13 M_sun/h to test the robustness of mass proxies against changing the physical processes included in simulations (thermal conduction, artificial viscosity, cooling and star formation, galactic winds and AGN feedback). We find the M-Y_X scaling relation to be the least sensitive one to variations of the ICM physics, with its slope and redshift evolution close to the self-similar model predictions. The distribution of the scatter around the best-fitting relations is close to a log-normal one. M_gas has the smallest scatter in mass, with values of sigma_lnM = 0.04-0.06, depending on the physics included in the simulation, and with a mild dependence on redshift. The M-T relation is the one with the largest scatter, with sigma_lnM > 0.1 at z=0, increasing to > 0.15 at z=1. The intrinsic scatter in the M-Y_X relation is slightly larger than in the M-M_gas relation. These results confirm that both Y_X and M_gas mass proxies are well suited for cosmological applications of future large X-ray surveys. [abridged]
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We review the methods adopted to reconstruct the mass profiles in X-ray luminous galaxy clusters. We discuss the limitations and the biases affecting these measurements and how these mass profiles can be used as cosmological proxies.
Recent X-ray observations of galaxy clusters show that the distribution of intra-cluster medium (ICM) metallicity is remarkably uniform in space and time. In this paper, we analyse a large sample of simulated objects, from poor groups to rich clusters, to study the dependence of the metallicity and related quantities on the mass of the systems. The simulations are performed with an improved version of the Smoothed-Particle-Hydrodynamics texttt{GADGET-3} code and consider various astrophysical processes including radiative cooling, metal enrichment and feedback from stars and active galactic nuclei (AGN). The scaling between the metallicity and the temperature obtained in the simulations agrees well in trend and evolution with the observational results obtained from two data samples characterised by a wide range of masses and a large redshift coverage. We find that the iron abundance in the cluster core ($r<0.1R_{500}$) does not correlate with the temperature nor presents a significant evolution. The scale invariance is confirmed when the metallicity is related directly to the total mass. The slope of the best-fitting relations is shallow ($betasim-0.1$) in the innermost regions ($r<0.5R_{500}$) and consistent with zero outside. We investigate the impact of the AGN feedback and find that it plays a key role in producing a constant value of the outskirts metallicity from groups to clusters. This finding additionally supports the picture of early enrichment.
Using archival X-ray observations and a log-normal population model, we estimate constraints on the intrinsic scatter in halo mass at fixed optical richness for a galaxy cluster sample identified in Dark Energy Survey Year-One (DES-Y1) data with the redMaPPer algorithm. We examine the scaling behavior of X-ray temperatures, $T_X$, with optical richness, $lambda_{RM}$, for clusters in the redshift range $0.2<z<0.7$. X-ray temperatures are obtained from Chandra and XMM observations for 58 and 110 redMaPPer systems, respectively. Despite non-uniform sky coverage, the $T_X$ measurements are $> 50%$ complete for clusters with $lambda_{RM} > 130$. Regression analysis on the two samples produces consistent posterior scaling parameters, from which we derive a combined constraint on the residual scatter, $sigma_{ln Tx | lambda} = 0.275 pm 0.019$. Joined with constraints for $T_X$ scaling with halo mass from the Weighing the Giants program and richness--temperature covariance estimates from the LoCuSS sample, we derive the richness-conditioned scatter in mass, $sigma_{ln M | lambda} = 0.30 pm 0.04, _{({rm stat})} pm 0.09, _{({rm sys})}$, at an optical richness of approximately 70. Uncertainties in external parameters, particularly the slope and variance of the $T_X$--mass relation and the covariance of $T_X$ and $lambda_{RM}$ at fixed mass, dominate the systematic error. The $95%$ confidence region from joint sample analysis is relatively broad, $sigma_{ln M | lambda} in [0.14, , 0.55]$, or a factor ten in variance.
We analyse cosmological hydrodynamical simulations of galaxy clusters to study the X-ray scaling relations between total masses and observable quantities such as X-ray luminosity, gas mass, X-ray temperature, and $Y_{X}$. Three sets of simulations are performed with an improved version of the smoothed particle hydrodynamics GADGET-3 code. These consider the following: non-radiative gas, star formation and stellar feedback, and the addition of feedback by active galactic nuclei (AGN). We select clusters with $M_{500} > 10^{14} M_{odot} E(z)^{-1}$, mimicking the typical selection of Sunyaev-Zeldovich samples. This permits to have a mass range large enough to enable robust fitting of the relations even at $z sim 2$. The results of the analysis show a general agreement with observations. The values of the slope of the mass-gas mass and mass-temperature relations at $z=2$ are 10 per cent lower with respect to $z=0$ due to the applied mass selection, in the former case, and to the effect of early merger in the latter. We investigate the impact of the slope variation on the study of the evolution of the normalization. We conclude that cosmological studies through scaling relations should be limited to the redshift range $z=0-1$, where we find that the slope, the scatter, and the covariance matrix of the relations are stable. The scaling between mass and $Y_X$ is confirmed to be the most robust relation, being almost independent of the gas physics. At higher redshifts, the scaling relations are sensitive to the inclusion of AGNs which influences low-mass systems. The detailed study of these objects will be crucial to evaluate the AGN effect on the ICM.
To better constrain models of cool core galaxy cluster formation, we have used X-ray observations taken from the Chandra and ROSAT archives to examine the properties of cool core and non-cool core clusters, especially beyond the cluster cores. We produced X-ray images, surface brightness profiles, and hardness ratio maps of 30 nearby rich Abell clusters (17 cool cores and 13 non-cool cores). We show that the use of double beta-models with cool core surface brightness profiles and single beta-models for non-cool core profiles yield statistically significant differences in the slopes (i.e., beta values) of the outer surface brightness profiles, but similar cluster core radii, for the two types of clusters. Hardness ratio profiles as well as spectroscopically-fit temperatures suggest that non-cool core clusters are warmer than cool core clusters of comparable mass beyond the cluster cores. We compared the properties of these clusters with the results from analogously reduced simulations of 88 numerical clusters created by the AMR Enzo code. The simulated surface brightness profiles have steeper beta-model fits in the outer cluster regions for both cool cores and non-cool cores, suggesting additional ICM heating is required compared to observed cluster ICMs. Temperature and surface brightness profiles reveal that the simulated clusters are over-cooled in their cores. As in the observations, however, simulated hardness ratio and temperature profiles indicate that non-cool core clusters are warmer than cool core clusters of comparable mass far beyond the cluster cores. The general similarities between observations and simulations support a model described in Burns et al. 2008 suggesting that non-cool core clusters suffered early major mergers destroying nascent cool cores.
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