Scaling relations for galaxy clusters in the Millennium-XXL simulation (original) (raw)
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2009
Scaling relations among galaxy cluster observables, which will become available in large future samples of galaxy clusters, could be used to constrain not only cluster structure, but also cosmology. We study the utility of this approach, employing a physically motivated parametric model to describe cluster structure, and applying it to the expected relation between the Sunyaev-Zel'dovich decrement (S_\nu) and the emission-weighted X-ray temperature (T_ew). The slope and normalization of the entropy profile, the concentration of the dark matter potential, the pressure at the virial radius, and the level of non-thermal pressure support, as well as the mass and redshift-dependence of these quantities are described by free parameters. With a suitable choice of fiducial parameter values, the cluster model satisfies several existing observational constraints. We employ a Fisher matrix approach to estimate the joint errors on cosmological and cluster structure parameters from a measurement of S_\nu vs. T_ew in a future survey. We find that different cosmological parameters affect the scaling relation differently: predominantly through the baryon fraction (\Omega_m and \Omega_b), the virial overdensity (w_0 and w_a for low-z clusters) and the angular diameter distance (w_0, w_a for high-z clusters; \Omega_DE and h). We find that the cosmology constraints from the scaling relation are comparable to those expected from the number counts (dN/dz) of the same clusters. The scaling relation approach is relatively insensitive to selection effects and it offers a valuable consistency check; combining the information from the scaling relation and dN/dz is also useful to break parameter degeneracies and help disentangle cluster physics from cosmology.
Unifying X-ray Scaling Relations from Galaxies to Clusters
Monthly Notices of the Royal Astronomical Society, 2015
We examine a sample of 250 000 `locally brightest galaxies' selected from the Sloan Digital Sky Survey to be central galaxies within their dark matter haloes. We stack the X-ray emission from these haloes, as a function of the stellar mass of the central galaxy, using data from the ROSAT All-Sky Survey. We detect emission across almost our entire sample, including emission which we attribute to hot gas around galaxies spanning a range of 1.2 dex in stellar mass (corresponding to nearly two orders of magnitude in halo mass) down to M* = 10^10.8 M⊙ (M500 ≈ 10^12.6 M⊙). Over this range, the X-ray luminosity can be fit by a power law, either of stellar mass or of halo mass. From this, we infer a single unified scaling relation between mass and LX which applies for galaxies, groups, and clusters. This relation has a slope steeper than expected for self-similarity, showing the importance of non-gravitational heating. Assuming this non-gravitational heating is predominately due to AGN feedback, the lack of a break in the relation shows that AGN feedback is tightly self-regulated and fairly gentle, in agreement with the predictions of recent high-resolution simulations. Our relation is consistent with established measurements of the LX-LK relation for elliptical galaxies as well as the LX-M500 relation for optically selected galaxy clusters. However, our LX-M500 relation has a normalization more than a factor of 2 below most previous relations based on X-ray-selected cluster samples. We argue that optical selection offers a less biased view of the LX-M500 relation for mass-selected clusters.
Galaxy cluster cosmology from X-ray surveys of the hot and energetic Universe
Proceedings of the International Astronomical Union
We discuss recent advances and prospects in our understanding of the formation of structures on cosmic scales based on surveys of galaxy clusters in the X-ray bands. We highlight the interaction between observations and numerical simulations of the X-ray sky. We show how future surveys will unveil the nature of the dark energy and study its evolution with time.