Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-05-12
Astronomy and Astrophysics
Astrophysics
aastex style, 14 pages, 3 eps figures. Major changes included. Accepted for publication in GRG
Scientific paper
We present an alternative for the description of galactic halos based on Tsallis' non--extensive entropy formalism; on this scheme, halos are stellar polytropes characterized by three parameters, the central density, $\rho_c$, the central velocity dispersion, $\sigma_c$ and the polytropic index, $n$. To evaluate these parameters we take the Navarro-Frenk-White paradigm as a comparative model and make the following assumptions: both halo models must have the same virial mass, the same total energy and the same maximal velocity. These three conditions fix all the parameters for a given stellar polytrope allowing us to compare both halo models. The halos studied have virial masses on the range $10^{12}-10^{15} M_\odot$, and it was found after the analysis that they are described, at all scales, by almost the same polytropic index, $n\approx 4.8$, implying an empirical estimation of Tsallis non--extensive parameter for this type of dynamical systems: $q\approx 1.3$.
Cabral-Rosetti Luis G.
Matos Tonatiuh
Nunez Darío
Sussman Roberto A.
Zavala Jesus
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