Victor Marian (Austria)
marian @ mpia.de
The properties of the cold interstellar medium in high-redshift galaxies
With the feedback of Active Galatic Nuclei (AGN) possibly playing a role in the truncation of star formation and therefore severely affecting the evolution of a galaxy, it is of utmost interest to understand the processes involved in the growth of black holes. For decades, it was a widely accepted scenario that the occurrence of AGNs are a result of a merger of gas-rich galaxies. However, over the last years the relevance of major interactions and the growth of BHs has been extensively tested, leading to a model in which the merging of two gas-rich galaxies is playing a sub-dominant part for the occurrence of an AGN. This circumstance holds in particular true for the majority of the black holes (stellar mass < 1011.7 solar mass) since z~1 (Cisternas+ 11), but also black holes with the highest masses at z = 2 (Mechtley+ 17) and z = 0.2 (in prep.)
The focus of this thesis is now whether this conclusion is also valid for black holes with highest accretion rates (L/Ledd > 0.3). As large amounts of gas and its transfer to the central region is needed, it may very well be that for this particular population of black holes major mergers are still the best or maybe only suitable mechanism. To examine this question we analyze the merger fractions of 21 QSO host galaxies at z = 2 (peak of black hole growth), observed by HST and 19 at z = 0.2 observed with VLT/FORS2 and compare them to the fractions of two matched samples of inactive galaxies. As all other parameters (mass, redshift) between the QSO samples and the respective selections of inactive galaxies are comparable, a significant increase of the merger fractions in regard to the QSOs means that major merging is in those particular cases a trigger for the growth of black holes.
Supervisors: Knud Jahnke (MPIA)