%0 Generic
%A Herpich, Jakob
%C Heidelberg
%D 2017
%F heidok:22958
%R 10.11588/heidok.00022958
%T On the Physical Origin of Radial Surface Density Profiles in Disk Galaxies
%U https://archiv.ub.uni-heidelberg.de/volltextserver/22958/
%X Observations have long established that the radial stellar surface density profiles in disk galaxies are nearly exponential (Type-I profiles). Stellar disks in numerical simulations also tend to approach an exponential profile. Deep imaging has revealed systematic deviations in the profile at large galactocentric radii. Beyond a break the profile may continue with a steeper (Type-II) or shallower (Type-III) exponential profile. In this thesis, I present numerical and analytical models that aim towards a physical understanding of how such profiles come about. I carried out numerical simulations designed to give extensive control over the physical conditions of disk galaxy formation. On this basis, I argue that the type of profile correlates with the initial spin of a galaxy’s host dark matter halo: Type-II/III disks are hosted by high-/low-spin halos. Type-I disks occur at intermediate spins. The formation mechanism for the Type-II disks is consistent with previous results in the literature. Through a very detailed analysis of the low-spin simulations I show that the formation of Type-III profiles can be linked to the formation of a strong bar in low-spin halos. Observational predictions are provided to test the presented hypotheses.  The evolution of the radial disk structure can be interpreted as shuffling of the individual stars’ angular momenta. Maximizing a suitably defined entropy in stellar angular momentum space yields an analytic prediction for the radial surface density profiles, given any galactic rotation curve and the corresponding stellar mass and angular momentum of the disk. I carefully compare this result with observational data and simulated disks. It gives a fair match to observations and is in very good agreement with those simulations that provide the closest match to the model assumption of perfectly circular stellar orbits.