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Regulation of star formation in giant galaxies by precipitation, feedback and conduction


The Universe’s largest galaxies reside at the centres of galaxy clusters and are embedded in hot gas that, if left undisturbed, would cool quickly and create many more new stars than are actually observed1,2,3,4,5. Cooling can be regulated by feedback from accretion of cooling gas onto the central black hole, but requires an accretion rate finely tuned to the thermodynamic state of the hot gas6,7. Theoretical models in which cold clouds precipitate out of the hot gas via thermal instability and accrete onto the black hole exhibit the necessary tuning8,9,10. Recent observational evidence shows that the abundance of cold gas in the centres of clusters increases rapidly near the predicted threshold for instability11. Here we report observations showing that this precipitation threshold extends over a large range in cluster radius, cluster mass and cosmic time. We incorporate the precipitation threshold into a framework of theoretical models for the thermodynamic state of hot gas in galaxy clusters. According to that framework, precipitation regulates star formation in some giant galaxies, while thermal conduction prevents star formation in others if it can compensate for radiative cooling and shut off precipitation.

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Figure 1: Hot-gas cooling time as a function of radius in galaxy clusters.
Figure 2: Hot-gas cooling time as a function of radius in galaxy clusters of differing temperatures.
Figure 3: Evolution of radial gas density and cooling-time profiles in galaxy clusters.


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G.M.V. and M.D. acknowledge NSF support through grant AST-0908819. G.L.B. acknowledges NSF AST-1008134, AST-1210890, NASA grant NNX12AH41G, and XSEDE Computational resources. M.McD. acknowledges support by NASA through a Hubble Fellowship grant HST-HF51308.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555.

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G.M.V.: theoretical models, data interpretation, manuscript preparation; M.D.: data analysis, data interpretation, discussions, manuscript review; G.L.B.: theoretical models, discussions, manuscript review; M.McD.: data analysis, discussions, manuscript preparation, manuscript review.

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Correspondence to G. M. Voit.

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The authors declare no competing financial interests.

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Voit, G., Donahue, M., Bryan, G. et al. Regulation of star formation in giant galaxies by precipitation, feedback and conduction. Nature 519, 203–206 (2015).

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