Entropy of gas and dark matter in galaxy clusters

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dc.creatorFaltenbacher, A.
dc.creatorHoffman, Y.
dc.creatorGottloeber, S.
dc.creatorYepes, G.
dc.date2006-08-15
dc.date2007-06-08
dc.date.accessioned2026-07-07T10:23:26Z
dc.date.available2026-07-07T10:23:26Z
dc.descriptionOn the basis of a large scale 'adiabatic', namely non-radiative and non-dissipative, cosmological smooth particle hydrodynamic simulation we compare the entropy profiles of the gas and the dark matter (DM) in galaxy clusters. The quantity K_g = T_g ρ_g^{-2/3} provides a measure for the entropy of the intra-cluster gas. By analogy with the thermodynamic variables of the gas the velocity dispersion of the DM is associated with a formal temperature and thereby K_DM = σ_DM^2 ρ_DM^{-2/3} is defined. This DM entropy is related to the DM phase space density by K_DM \propto Q_DM^{-2/3}. In accord with other studies the DM phase space density follows a power law behaviour, Q_DM \propto r^{-1.82}, which corresponds to K_DM \propto r^{1.21}. The simulated intra-cluster gas has a flat entropy core within (0.8 \pm 0.4) R_s, where R_s is the NFW scale radius. The outer profile follows the DM behaviour, K_g \propto r^{1.21}, in close agreement with X-ray observations. Upon scaling the DM and gas densities by their mean cosmological values we find that outside the entropy core a constant ratio of K_g / K_{DM} = 0.71 \pm 0.18 prevails. By extending the definition of the gas temperature to include also the bulk kinetic energy the ratio of the DM and gas extended entropy is found to be unity for r > 0.8 R_s. The constant ratio of the gas thermal entropy to that of the DM implies that observations of the intra-cluster gas can provide an almost direct probe of the DM.
dc.description7 pages, 8 figures, accepted for publication in MNRAS, web page of the The Marenostrum Numerical Cosmology Project : http://astro.ft.uam.es/~marenostrum/
dc.identifierhttps://arxiv.org/abs/astro-ph/0608304
dc.identifierhttp://arxiv.org/abs/astro-ph/0608304
dc.identifierMon.Not.Roy.Astron.Soc.376:1327-1334,2007
dc.identifierdoi:10.1111/j.1365-2966.2007.11529.x
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/175827
dc.subjectAstrophysics
dc.titleEntropy of gas and dark matter in galaxy clusters
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