Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 467, Issue 2, Pages 2066-2084Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stx243
Keywords
ISM: evolution; ISM: structure; galaxies: evolution; galaxies: formation; galaxies: haloes; intergalactic medium
Categories
Funding
- Research Collaboration Award at the University of Western Australia
- Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO) [CE110001020]
- CONICYT Doctoral Fellowship Programme
- BIS National E-infrastructure capital [ST/K00042X/1]
- STFC capital [ST/H008519/1]
- STFC DiRAC Operation [ST/K003267/1]
- Durham University
- Dutch National Computing Facilities Foundation (NCF)
- Netherlands Organisation for Scientific Research (NWO)
- European Research Council under the European Union's Seventh Framework Programme (FP7) / ERC [278594]
- STFC [ST/I001573/1, ST/I00162X/1, ST/H008519/1, ST/L00075X/1, ST/K00042X/1, ST/M007006/1, ST/P000541/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/I001573/1, ST/P000541/1, ST/H008519/1, ST/I00162X/1, ST/M007006/1, ST/K00042X/1, ST/L00075X/1] Funding Source: researchfish
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We use the hydrodynamic, cosmological EAGLE simulations to investigate how the hot gas in haloes condenses to form and grow galaxies. We select haloes from the simulations that are actively cooling and study the temperature, distribution and metallicity of their hot, cold and transitioning `cooling' gas, placing these in the context of semi-analytic models. Our selection criteria lead us to focus on Milky Way-like haloes. We find that the hot-gas density profiles of the haloes form a progressively stronger core over time, the nature of which can be captured by a beta profile that has a simple dependence on redshift. In contrast, the hot gas that will cool over a time-step is broadly consistent with a singular isothermal sphere. We find that cooling gas carries a few times the specific angular momentum of the halo and is offset in spin direction from the rest of the hot gas. The gas loses similar to 60 per cent of its specific angular momentum during the cooling process, generally remaining greater than that of the halo, and it precesses to become aligned with the cold gas already in the disc. We find tentative evidence that angular-momentum losses are slightly larger when gas cools on to dispersion-supported galaxies. We show that an exponential surface density profile for gas arriving on a disc remains a reasonable approximation, but a cusp containing similar to 20 per cent of the mass is always present, and disc scale radii are larger than predicted by a vanilla Fall & Efstathiou model. These scale radii are still closely correlated with the halo spin parameter, for which we suggest an updated prescription for galaxy formation models.
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