Structure and evolution of magnetized clusters: entropy profiles, S - T and LX - T relations
Abstract
We study the impact of an intracluster magnetic field on the main structural properties of clusters and groups of galaxies: the radial density and entropy profiles, the entropy - temperature relation and the X-ray luminosity - temperature relation for groups and clusters of galaxies. To this aim, we develop a description of the intra-cluster gas based on the Hydrostatic Equilibrium condition and on the Magnetic Virial Theorem in the presence of a radial distribution of the magnetic field B(r) = B* (ρ_g(r))α, with α ≈ 0.9, as the one indicated by observations and numerical simulation. Our analysis shows that such a description is able to provide, at once, a possible explanation of three problematic aspects of the cluster structure: i) the flattening of the entropy profile in the cluster center; ii) the flatness of the S - T relation; iii) the increasing steepening of the L_X-T relation from the cluster scale towards the group scales. The available entropy and X-ray luminosity data indicate that an increase of the magnetic field B* ∼ T0.5 ± 0.1 is required to reproduce at the same time both the S - T and the L_X-T relations. It follows that a consistent description of the magnetized ICM can provide a simple explanation of several (or of all) of these still open problems, and thus weakens the need for the inclusion of other non-gravitational effects which have been proposed so far for the explanation of some of these features. This (initial, but not conclusive) analysis can be regarded as a starting point for a more refined analytical exploration of the physics of the magnetized intra-cluster medium, and it provides testable predictions that can be proven or disproven with the next coming sensitive observations of groups and clusters in the X-ray band and in the radio frequency band.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- May 2007
- DOI:
- 10.1051/0004-6361:20065405
- arXiv:
- arXiv:astro-ph/0701853
- Bibcode:
- 2007A&A...466..421C
- Keywords:
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- cosmology: theory;
- galaxies: clusters: general;
- Astrophysics
- E-Print:
- 18 pages, 19 figures, A&