Symbiosis or not: the interplay of massive black holes and their host galaxies

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The aim of this project is to unravel the importance of various pathways of growth of massive black holes and their host galaxies. This will be done by determining the masses of massive black holes in nearby galaxies, describing the motion of stars via dynamical models and interpreting these through scenarios of massive black hole and galaxy formation. Massive black holes are thought to have played a major role in shaping galaxies and intergalactic matter. This is evident from the empirical scaling relations between the masses of massive black holes and the global properties of host galaxies, such as their mass or luminosity. The correlation is very tight with a small scatter, but we do not understand why, nor if the massive black holes and their host galaxies grow symbiotically or one component dominates in their evolution. The consequence of the observing difficulties is that the scaling relations are still poorly known, black hole masses are typically derived in only some types of galaxies and the black hole growth processes are not even constrained in galaxies for which black hole masses exist. This project provides the state-of-art observation with adaptive optics integral-field spectroscopy in order to derive a significant number of measurements of black hole masses (~20% increase to the total number of measurements), over a range of galaxy properties. In particular, this will be achieved by measuring the motions of stars and using it to constrain dynamical models. The dynamical models will provide the black hole masses and the detailed information on the types of stellar orbits. The methods applied will test the robustness of the black hole mass determinations with respect to the assumptions on the dark matter content of galaxies, with a potential for becoming the standard in the field. The sample is selected to probe the gaps in the scaling correlations, and to investigate the scenarios describing the growth of massive black holes. In a symbiotic growth scenario, massive black holes grow through merging of progenitor black holes, while in the other they grow by accretion of gas. The two scenarios leave different imprints on the orbits of stars in the central regions of galaxies: the merger scenario predicts a deficit of orbits which come close to the massive black holes, as those stars are ejected from the nucleus. With most of the necessary tools and all data already in hand, it will be possible to determined the black hole masses, characterise the motion of stars in the vicinity of massive black holes and distinguish between competing scenarios.