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Simple models of cooling flows | | Christian R. Kaiser
; James J. Binney
; | | Date: |
4 Jul 2002 | | Subject: | astro-ph | | Affiliation: | Southampton, Oxford | | Abstract: | A semi-analytic model of cluster cooling flows is presented. The model assumes that episodic nuclear activity followed by radiative cooling without mass-dropout cycles the cluster gas between a relatively homogeneous, nearly isothermal post-outburst state and a cuspy configuration in which a cooling catastrophe initiates the next nuclear outburst. Fitting the model to Chandra data for the Hydra cluster, a lower limit of $284Myr$ until the next outburst of Hydra A is derived. Density, temperature and emission-measure profiles at several times prior to the cooling catastrophe are presented. It proves possible to fit the mass $M(sigma)$ with entropy index $P
ho^{-gamma}$ less than $sigma$ to a simple power-law form, which is almost invariant as the cluster cools. We show that radiative cooling automatically establishes this power-law form if the entropy index was constant throughout the cluster gas at some early epoch or after an AGN activity cycle. To high precision, the central value of $sigma$ decreases linearly in time. The fraction of clusters in a magnitude-limited sample that have gas cooler than $T$ is calculated, and is shown to be small for $T=2keV$. Similarly, only 1 percent of clusters in such a sample contain gas with $P
ho^{-gamma} < 2keVcm^2$. Entropy production in shocks is shown to be small. The entropy that is radiated from the cluster can be replaced if a few percent of the cluster gas passes through bubbles heated during an outburst of the AGN. | | Source: | arXiv, astro-ph/0207111 | | Services: | Forum | Review | PDF | Favorites | |
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