The evolution of cooling flows - Self-similar cooling waves

Abstract

Similarity solutions are presented for the time-dependent evolution ofcooling flows. A cooling flow expands when the cooling time computedfrom the initial gas distribution increases with radius. If certainsimplifying conditions are met, the evolution of the resulting coolingwave becomes self-similar. The similarity solutions obtained hereassumed subsonic flow, which is valid in the outer parts of observedcooling flows; they are matched to transonic accretion solutions validin the central parts. The models are applied to the cooling flow ontoM87, with unsatisfactory agreement at small radius. A local linearstability analysis shows that the similarity solution suffers isobaricthermal instability, suggesting that the neglect of star formation maybe responsible for the poor agreement. The similarity solution suggeststhat the cooling flow around M87 was more vigorous in the past.