Abstract

Black holes of millions to billion solar masses in the centres of nearby galaxies raise the question how and when these black holes were created. I will give an overview of some investigations of the origin, growth and consequences of the presence of such black holes studied with X-ray surveys including from the new all-sky surveyor eROSITA and multi-wavelength information. In understanding the host galaxies growing their black holes, a on-going challenge is that light from Active Galactic Nuclei contaminates the emission of galaxies, making the measurement of stellar masses and star-formation rates notoriously unreliable. Overly high masses when the AGN model is incomplete are typical. This prevents evolutionary tests comparing black hole and host galaxy properties. Our group developed a novel data-driven benchmark data set where host galaxy masses and AGN properties are known, and tested a variety of SED fitting codes to critically evaluate their ability to infer host galaxy properties. Finally, we present an unbiased SED fitting method, GRAHSP , Grasping Reliably the AGN Host Stellar Population, to test the evolution of supermassive black holes in the centres of galaxies.