%0 Generic
%A Bosco, Felix
%C Heidelberg
%D 2021
%F heidok:29879
%R 10.11588/heidok.00029879
%T Probing the Growth of Black Holes at the Limit of Large Telescopes
%U https://archiv.ub.uni-heidelberg.de/volltextserver/29879/
%X Direct kinematical measurements of black hole (BH) masses require to resolve the sphere of influence at sub-milliarcsecond scales. Here, two novel observational approaches are studied that exhaust the resolution limit of modern large telescopes in order to allow for tighter constraints on masses and growth mechanisms of BHs. The first approach applies holographic speckle imaging techniques to near-infrared images after partial atmospheric turbulence correction. Based on simulations and observational data, we show that the combination of techniques recovers the diffraction limit of 8 m-class telescopes for stars too faint for classical speckle imaging. This approach will allow for tracing BHs directly via stellar kinematics. The second technique uses the spectroastrometric signal of the quasar broad emission line region in order to constrain its geometric and kinematic structure. We extract this signal from adaptive-optics-assisted near-infrared spectroscopy with an 8 m telescope and carefully study the uncertainties. The comparison of the data to our model allows us to report on the first tentative detection of the spectroastrometric signal of a luminous quasar and thereby for constraining its BH mass, the first direct measurement beyond a redshift of z = 2 and out of the detection range of reverberation mapping or optical interferometry.