A Simple and Accurate Model for Intracluster Gas

Abstract

Starting with the well-known NFW dark matter halo distribution, we construct a simple polytropic model for the intracluster medium that is in good agreement with high-resolution numerical hydrodynamic simulations, apply this model to a very large scale concordance dark matter simulation, and compare the resulting global properties with recent observations of X-ray clusters, including the mass-temperature and luminosity-temperature relations. We make allowances for a nonnegligible surface pressure, removal of low-entropy (short cooling time) gas, energy injection due to feedback, and a relativistic (nonthermal) pressure component. A polytropic index n ¼ 5 (À ¼ 1:2) provides a good approximation to the internal gas structure of massive clusters (except in the very central regions where cooling becomes important) and allows one to recover the observed M 500 -T, L X -T, and T /n 2/3 e / T 0:65 relations. Using these concepts and generalizing this method so that it can be applied to fully three-dimensional N-body simulations, one can predict the global X-ray and SZE trends for any specified cosmological model. We find a good fit to observations when assuming that 12% of the initial baryonic mass condenses into stars, that the fraction of rest mass of this condensed component transferred back to the remaining gas (feedback) is 3:9 ; 10 À5 , and that the fraction of total pressure from a nonthermal component is near 10%.

f(R)-gravity model of the Sunyaev-Zeldovich profile of the Coma cluster compatible with Planck data

“…We found that the preferred value of the polytropic index is γ = 1.44 +0.10 −0.17 . The best fit value is compatible at the 1.5σ level with γ ∼ 1.2, the value preferred by observations and numerical simulations [80][81][82][83]. Since the polytropic index is determined by physical processes that drive the cluster collapse and its subsequent relaxation [84], our results support the idea that analytic f (R) models without a dominant DM component can explain the structure of galaxy clusters as the ΛCDM model.…”

The tau of galaxy clusters

“…In cross-correlation the combinations X-ray and tSZ observations have yielded stacked gas density profiles that go beyond R 500 (e.g., Planck Collaboration et al 2013a; Eckert et al 2012), for a sub-set of massive clusters. Beyond R 500 there are theoretical gas density profiles from analytic calculations (e.g., Komatsu & Seljak 2001;Ostriker et al 2005;Patej & Loeb 2015) and predictions from numerical simulations (e.g., Roncarelli et al 2006;Nagai et al 2007;Vazza et al 2010;Pike et al 2014), with some of simulations provided a fitting function to their results. Like most halo profiles simulations show that the gas density profile is close to self-similar, but recently it was shown that at large radii self-similarity is broken by the mass accretion history of the halo (Lau et al 2015).…”

Simulations of the Sunyaev-Zel'dovich Power Spectrum With Active Galactic Nucleus Feedback

“…The power spectrum is then obtained using an analytic fit to "halo model" abundances. So far the SPT and ACT have only used the KS template and a related semi-analytic one (Ostriker et al 2005;Bode et al 2009). This model (Sehgal et al 2010, hereafter S10) allows map generation by painting dark matter halos in N-body simulations with gas.…”