http://arxiv.org/abs/1803.01923
We compare the mass cooling rates and cumulative cooled-down masses predicted by several semi-analytical (SA) cooling models with hydrodynamical simulations performed using the grid-based code AREPO. The SA cooling models are the new cooling model introduced in Hou et al. (2017), along with two earlier GALFORM cooling models and the cooling models in the L-GALAXIES and MORGANA SA galaxy formation models. We find that the predictions of the new cooling model generally agree the best with the simulations. For halos with $M_{\rm halo}\lesssim 3\times 10^{11}\,{\rm M}{\odot}$ , the SA models predict that radiative cooling is faster than gravitational infall. Even though SA models assume that gas falls onto galaxies from a spherical gas halo, while the simulations show that the cold gas is accreted through non-spherical filaments, both methods predict similar mass cooling rates, because in both cases the gas accretion onto galaxies is limited by the gravitational infall timescale. For halos with $M{\rm halo}\gtrsim 10^{12}\,{\rm M}_{\odot}$ , gas in the simulations typically cools from a roughly spherical hot gas halo, as assumed in the SA models, but the halo gas only gradually contracts during cooling, leading to compressional heating. SA models ignore this compressional heating, and so overestimate mass cooling rates by factors of a few. At low redshifts halo major mergers or a sequence of successive smaller mergers are seen in the simulations to strongly heat the hot gas halo and suppress cooling, while mergers at high redshifts do not suppress cooling, because the gas filaments are difficult to heat up. The new SA cooling model best captures these effects of halo mergers.
J. Hou, C. Lacey and C. Frenk
Wed, 7 Mar 18
45/65
Comments: 26 pages, 15 figures, to be submitted to MNRAS
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