%0 Generic %1 mcnamara2016mechanism %A McNamara, B. R. %A Russell, H. R. %A Nulsen, P. E. J. %A Hogan, M. T. %A Fabian, A. C. %A Pulido, F. %A Edge, A. C. %D 2016 %K agn cooling feedback galaxies massive %T A Mechanism for Stimulated AGN Feedback in Massive Galaxies %U http://arxiv.org/abs/1604.04629 %X Observation shows that cooling instabilities leading to nebular emission, molecular gas, and star formation in giant galaxies are formed behind buoyantly-rising X-ray bubbles inflated by radio jets launched from massive nuclear black holes. We propose a model where molecular clouds condense from hot but relatively low entropy gas lifted by X-ray bubbles to an altitude where its cooling time is shorter than the time required for it to fall to its equilibrium location in the galaxy i.e., t_c/t_I <~1$. Here the infall time can exceed the free-fall time, t_ff, by factors of a few. This mechanism, which we refer to as stimulated feedback, is motivated by recent ALMA observations of central galaxies in clusters and groups revealing molecular clouds apparently forming in the wakes of rising X-ray bubbles and with surprisingly low cloud velocities. Supported by recent numerical simulations, our model would naturally sustain a continual feedback-loop in galaxies fuelled by cooling gas stimulated by radio-mechanical feedback itself, that otherwise stabilizes cooling atmospheres on larger scales. The observed cooling time threshold for the onset of nebular emission and star formation of ~ 5x10^8 yr may result from the limited ability of radio bubbles to lift low entropy gas to an altitude where thermal instabilities can ensue. The molecular clouds condensing from the outflowing hot gas are unlikely to escape, but instead return to the central galaxy in a circulating flow.

@misc{mcnamara2016mechanism, abstract = {Observation shows that cooling instabilities leading to nebular emission, molecular gas, and star formation in giant galaxies are formed behind buoyantly-rising X-ray bubbles inflated by radio jets launched from massive nuclear black holes. We propose a model where molecular clouds condense from hot but relatively low entropy gas lifted by X-ray bubbles to an altitude where its cooling time is shorter than the time required for it to fall to its equilibrium location in the galaxy i.e., t_c/t_I <~1$. Here the infall time can exceed the free-fall time, t_ff, by factors of a few. This mechanism, which we refer to as stimulated feedback, is motivated by recent ALMA observations of central galaxies in clusters and groups revealing molecular clouds apparently forming in the wakes of rising X-ray bubbles and with surprisingly low cloud velocities. Supported by recent numerical simulations, our model would naturally sustain a continual feedback-loop in galaxies fuelled by cooling gas stimulated by radio-mechanical feedback itself, that otherwise stabilizes cooling atmospheres on larger scales. The observed cooling time threshold for the onset of nebular emission and star formation of ~ 5x10^8 yr may result from the limited ability of radio bubbles to lift low entropy gas to an altitude where thermal instabilities can ensue. The molecular clouds condensing from the outflowing hot gas are unlikely to escape, but instead return to the central galaxy in a circulating flow.}, added-at = {2016-04-19T09:38:00.000+0200}, author = {McNamara, B. R. and Russell, H. R. and Nulsen, P. E. J. and Hogan, M. T. and Fabian, A. C. and Pulido, F. and Edge, A. C.}, biburl = {https://www.bibsonomy.org/bibtex/215b9762342e4902b9a2be79382ee678c/miki}, description = {[1604.04629] A Mechanism for Stimulated AGN Feedback in Massive Galaxies}, interhash = {bb2b7ca6b8734c2d8c70f20a7b9b641a}, intrahash = {15b9762342e4902b9a2be79382ee678c}, keywords = {agn cooling feedback galaxies massive}, note = {cite arxiv:1604.04629Comment: Submitted to Ap.J}, timestamp = {2016-04-19T09:38:00.000+0200}, title = {A Mechanism for Stimulated AGN Feedback in Massive Galaxies}, url = {http://arxiv.org/abs/1604.04629}, year = 2016 }