Abstract
In several models of galaxy formation feedback occurs in cycles or mainly at high redshift. At times and in regions where feedback heating is ineffective, hot gas in the galaxy halo is expected to form a cooling flow, where the gas advects inward on a cooling timescale. Cooling flow solutions can thus be used as a benchmark for observations and simulations to constrain the timing and extent of feedback heating. Using analytic calculations and idealized 3D hydrodynamic simulations, we show that for a given halo mass and cooling function, steady-state cooling flows form a single-parameter family of solutions, while initially hydrostatic gaseous haloes converge on one of these solutions within a cooling time. The solution is thus fully determined once either the mass inflow rate M or the total halo gas mass are known. In the Milky Way halo, a cooling flow with M equal to the star formation rate predicts a ratio of the cooling time to the free-fall time of ∼10, similar to some feedback-regulated models. This solution also correctly predicts observed O VII and O VIII absorption columns, and the gas density profile implied by O VII and O VIII emission. These results suggest ongoing heating by feedback may be negligible in the inner Milky-Way halo. Extending similar solutions out to the cooling radius however underpredicts observed O VI columns around the Milky-Way and around other low-redshift star-forming galaxies. This can be reconciled with the successes of the cooling flow model with either a mechanism which preferentially heats the O VI-bearing outer halo, or alternatively if O VI traces cool photoionized gas beyond the accretion shock. We also demonstrate that the entropy profiles of some of the most relaxed clusters are reasonably well described by a cooling flow solution.
Original language | English (US) |
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Pages (from-to) | 2549-2572 |
Number of pages | 24 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 488 |
Issue number | 2 |
DOIs | |
State | Published - Sep 11 2019 |
Funding
We thank the referee, Prateek Sharma, for a thorough report and illuminating comments that significantly improved the paper. We thank also Mark Voit, Sean D. Johnson, and Zachary Hafen for detailed and insightful comments. We thank Michael McDonald for the entropy profiles fits used in Fig. 14. Jonathan Stern is supported by the CIERA Postdoctoral Fellowship Program. Drummond Fielding is supported by the Flatiron Institute, which is supported by the Simons Foundation. Claude-André Faucher-Giguère is supported by NSF through grants AST-1517491, AST-1715216, and CAREER award AST-1652522, by NASA through grants NNX15AB22G and 17-ATP17-0067, by STScI through grants HST-GO-14681.011, HST-GO-14268.022-A, and HST-AR-14293.001-A, and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. This work was supported in part by a Simons Investigator Award from the Simons Foundation and by NSF grant AST-1715070.
Keywords
- Galaxies: evolution
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science