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EnglishWe determine the critical size l_crit of a filament of cold (T~10^4 K) gas that is in radiative equilibrium with X-ray emitting gas at temperatures T_max ~ 10^6 - 10^8 K. Filaments smaller than l_crit will be rapidly evaporated, while longer ones will induce the condensation of the ambient medium. At fixed pressure P, l_crit increases as T_max^{11/4}, while at fixed T_max it scales as 1/P. It scales as f^(1/2), where f is the factor by which the magnetic field depresses the thermal conductivity below Spitzer's benchmark value. For plausible values of f, l_crit is similar to the lengths of observed filaments. In a cluster such as Perseus, the value of l_crit increases by over an order of magnitude between the centre and a radius of 100 kpc. If the spectrum of seed filament lengths l is strongly falling with l, as is natural, then these results explain why filaments are only seen within a few kiloparsecs of the centres of clusters, and are not seen in clusters that have no cooling flow. We calculate the differential emission measure as a function of temperature for the interface between filaments and ambient gas of various temperatures. We discuss the implications of our results for the origin of the galaxy luminosity function.
| Titolo: | Cold filaments in galaxy clusters: effects of heat conduction |
| Autore/i: | NIPOTI, CARLO; Binney J. |
| Autore/i Unibo: | |
| Anno: | 2004 |
| Rivista: | |
| Digital Object Identifier (DOI): | http://dx.doi.org/10.1111/j.1365-2966.2004.07628.x |
| Abstract: | We determine the critical size l_crit of a filament of cold (T~10^4 K) gas that is in radiative equilibrium with X-ray emitting gas at temperatures T_max ~ 10^6 - 10^8 K. Filaments smaller than l_crit will be rapidly evaporated, while longer ones will induce the condensation of the ambient medium. At fixed pressure P, l_crit increases as T_max^{11/4}, while at fixed T_max it scales as 1/P. It scales as f^(1/2), where f is the factor by which the magnetic field depresses the thermal conductivity below Spitzer's benchmark value. For plausible values of f, l_crit is similar to the lengths of observed filaments. In a cluster such as Perseus, the value of l_crit increases by over an order of magnitude between the centre and a radius of 100 kpc. If the spectrum of seed filament lengths l is strongly falling with l, as is natural, then these results explain why filaments are only seen within a few kiloparsecs of the centres of clusters, and are not seen in clusters that have no cooling flow. We calculate the differential emission measure as a function of temperature for the interface between filaments and ambient gas of various temperatures. We discuss the implications of our results for the origin of the galaxy luminosity function. |
| Data prodotto definitivo in UGOV: | 2005-09-30 10:02:13 |
| Appare nelle tipologie: | 1.01 Articolo in rivista |
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http://hdl.handle.net/11585/8405
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