Jakob Herpich

Jakob Herpich (Germany)
herpich @ mpia.de

A numerical model for explaining the observed morphology of disk galaxy profiles

Galaxies had been observed to have exponential radial surface brightness profiles. However, recent observations have revealed that the radial luminosity profiles in the outskirts of disk galaxies do not have a universal shape. They fall into three separate groups. They either continue exponentially out to the detection limit or they exhibit a two component exponential profile that steepens (down-bending) or gets shallower (up-bending) outside of a break region. As of now no model exists that can explain the formation of the latter profile. This thesis reports the results of a series of numerical smoothed particle
hydrodynamics (SPH) simulations of the formation of isolated disk galaxies. This numerical model is capable of reproducing all three kinds of observed disk galaxy profiles by tuning just one parameter: the initial spin parameter λ of the baryonic material. Galaxies that formed from low spin initial conditions exhibit an up-bending profile and down-bending profiles form from high spin initial conditions. Pure exponential disks only occur at a very sharp transition at lambda ~0.035. This could potentially explain the relatively low abundance of pure exponential disks in observed samples. Particular emphasis will be put on the physical mechanisms that cause up-bending profiles to form.

Supervisor: Hans-Walter Rix (MPIA)

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