The complex Interplay between Spin, Mass, and Morphology in Galaxies
by Adelheid Teklu
The evolution and distribution of the angular momentum of dark matter halos have been discussed in several studies over the last decades. In particular, the idea arose that angular momentum conservation should allow to infer the total angular momentum of the entire dark matter halo from measuring the angular momentum of the baryonic component, which is populating the center of the halo, especially for disk galaxies.
To test this idea and to understand the connection between the angular momentum of the dark matter halo and its galaxy, we use the Magneticum set of cosmological hydrodynamic simulations and extracted in total more than 2000 individual galaxies at different redshifts from the high resolution run of Box4. For each galaxy we could investigate the properties of the different constituents: the dark matter, the stars as well as the hot and the cold gas-phase.
The simulations successfully produce populations of spheroidal and disk galaxies self-consistently. Moreover, the specific angular momentum of stars in disk and spheroidal galaxies as function of their stellar mass compares very well with observational findings. The specific angular momentum of the stars in disk galaxies is slightly smaller compared to the specific angular momentum of the cold gas, again in good agreement with observations.
Thus, we are able to study the dependence of general halo properties on the morphology of the hosted galaxies. Interestingly, we found that simulations including the baryonic component show a dichotomy in the specific stellar angular momentum distribution when splitting the galaxies according to their morphological type. This dichotomy can also be seen in the spin parameter, where disk galaxies populate halos with slightly larger spin compared to spheroidal galaxies. We also found that disk galaxies preferentially populate halos in which the angular momentum vector of the dark matter component in the central part shows a better alignment with the angular momentum vector of the entire halo. Finally, we could prove that the specific angular momentum of the cold gas in disk galaxies is approximately 40 percent smaller than the specific angular momentum of the total dark matter halo and shows a significant scatter.
