The angular momentum structure of cosmic ray driven galactic outflows triggered by stream accretion

We display here videos of the gas column density evolution for 9 magneto-hydrodynamical simulations of galaxies including cosmic rays and Nbody particles for stars and dark matter, ran with the PIERNIK code. The goal is to study the creation and evolution of cosmic ray driven galactic winds, and in particular their angular momentum dependence and structure. These simulations model the evolution over 2 Gyr of a galactic disc receiving an external inflow of gas, representing the stream feed growth of galaxies from the intergalactic medium. The 8 first cases represent different parameters of this inflow ; we vary the velocity of the inflow (while keeping the mass flux constant) to represent input of different amounts of angular momentum, and the height of the inflow above the disc. The 9th simulation (NS for No Stream) does not include an inflow, as a reference case. The p1, p2, p3 and p4 simulations have an inflow arriving in the disc plane ; from p1 to p4 the inflow brings more and more angular momentum to the disc. Similarly, from o1 to o4 there is increasingly more angular momentum, but in these 4 cases the inflow arrives 20 kpc above the disc. We observe that the more angular momentum is brought to the disc, the weaker the resulting cosmic ray driven outflows are : the input of low angular momentum allows gas to leave the disc in bigger quantities and reach higher altitudes than for high angular momentum. The inflowing stream also triggers the formation of a ring in the galaxy in most cases, although stronger for the low angular momentum and out of plane cases. The NS case, without a stream triggering an enhanced star formation episode, shows the weakest outflows, as well as no ring formation.

For more details and further analysis, please refer to the corresponding paper :

Peschken, N. ; Hanasz, M. ; Naab, T. ; Wóltański, D.; Gawryszczak, A. 2021, MNRAS, 508, 4269