The internal dynamics of a dark matter structure may have the remarkable property that the local temperature in the structure depends on direction. This is parameterized by the velocity anisotropy β which must be zero for relaxed collisional structures, but has been shown to be nonzero in numerical simulations of dark matter structures. Here, we present a method for inferring the radial profile of the velocity anisotropy of the dark matter halo in a galaxy cluster from X-ray observables of the intracluster gas. This nonparametric method is based on a universal relation between the dark matter temperature and the gas temperature which is confirmed through numerical simulations. We apply this method to observational data and we find that β is significantly different from zero at intermediate radii. Thus, we find a strong indication that dark matter is effectively collisionless on the dynamical timescale of clusters, which implies an upper limit on the self-interaction cross-section per unit mass σ/m lsim 1 cm2 g-1. Our results may provide an independent way to determine the stellar mass density in the central regions of a relaxed cluster, as well as a test of whether a cluster is in fact relaxed.

Measurement of the dark matter velocity anisotropy in galaxy clusters / Host, O; Hansen, S. H.; Piffaretti, R; Morandi, A; Ettori, S; Kay, S. T.; Valdarnini, Riccardo. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - 690:1(2009), pp. 358-366. [10.1088/0004-637X/690/1/358]

Measurement of the dark matter velocity anisotropy in galaxy clusters

Valdarnini, Riccardo
2009-01-01

Abstract

The internal dynamics of a dark matter structure may have the remarkable property that the local temperature in the structure depends on direction. This is parameterized by the velocity anisotropy β which must be zero for relaxed collisional structures, but has been shown to be nonzero in numerical simulations of dark matter structures. Here, we present a method for inferring the radial profile of the velocity anisotropy of the dark matter halo in a galaxy cluster from X-ray observables of the intracluster gas. This nonparametric method is based on a universal relation between the dark matter temperature and the gas temperature which is confirmed through numerical simulations. We apply this method to observational data and we find that β is significantly different from zero at intermediate radii. Thus, we find a strong indication that dark matter is effectively collisionless on the dynamical timescale of clusters, which implies an upper limit on the self-interaction cross-section per unit mass σ/m lsim 1 cm2 g-1. Our results may provide an independent way to determine the stellar mass density in the central regions of a relaxed cluster, as well as a test of whether a cluster is in fact relaxed.
2009
690
1
358
366
https://doi.org/10.1088/0004-637X/690/1/358
Host, O; Hansen, S. H.; Piffaretti, R; Morandi, A; Ettori, S; Kay, S. T.; Valdarnini, Riccardo
File in questo prodotto:
File Dimensione Formato  
HO09.pdf

accesso aperto

Tipologia: Versione Editoriale (PDF)
Licenza: Non specificato
Dimensione 277.06 kB
Formato Adobe PDF
277.06 kB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11767/13802
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 35
  • ???jsp.display-item.citation.isi??? 34
social impact