The phase structure of cosmic ray driven outflows in stream fed disc galaxies
We display below videos of the gaseous evolution of 10 magneto-hydrodynamical simulations of galaxies run with the PIERNIK code, and described in our paper Peschken et al. (2023). The videos in the left column show the gas column density seen face-on and edge-on, while the right column shows the gas temperatures taken in slices.
The simulations include cooling and heating of the gas, cosmic rays and Nbody particles for stars and dark matter, with stellar particle creation. We aim at studying the impact of cosmic rays on galactic winds and outflows, and use the framework of stream feed growth of galaxies, by modeling the accretion of an external inflow of gas from the intergalactic medium for 1 Gyr. We obtain 10 simulations by varying the amount of angular momentum brought by the stream to the disc (changing the stream velocity), and by including or not cosmic rays in the simulation. Therefore, the "cr+t" simulations include both cosmic rays and thermal supernova feedback, while the "pt" simulations are pure thermal, i.e. without cosmic ray feedback. The stream velocity is increased from cr+t1 to cr+t5 (and similarly from pt1 to pt5), leading to discs with more angular momentum. Similarly to our previous paper (Peschken et al. 2021), we observe that increasing the angular momentum of the disc leads to a lower star formation rate, and to less outflows overall. We also observe significant differences between the cases with and without cosmic rays; cosmic rays simulations tend to launch more outflows, with cooler temperatures than in the pure thermal case. We furthermore found the presence of two gas phases in the outflows in the presence of cosmic rays: hot gas with low angular momentum leaving the disc deep into the halo, and a cooler (warm) gas phase with high angular momentum, which tends to stay in the vicinity of the disc.
For more details and further analysis, please refer to the corresponding paper :
Peschken, N. ; Hanasz, M. ; Naab, T. ; Wóltański, D.; Gawryszczak, A. 2023 MNRAS, 522, 5529