"How to Assemble an Overmassive Black Hole"

Abstract:

At the center of virtually all galaxies lies a supermassive black hole (SMBH) with a typical mass of ~0.5% of its host galaxy. Recently, JWST has discovered over-massive BHs (OMBH) at high redshift with M_BH/M_* ~10%, which have been interpreted as remnants from the rapid accretion of recently born SMBHs. However, the processes that can lead to OMBHs are poorly understood. In order to do so, we searched for OMBHs AGN at low redshift within the eROSITA Final Equatorial Depth Survey (eFEDS), covering ~140 deg². Eight OMBHs have been identified, providing the opportunity to study systems in rapid growth in the local Universe.

In eFEDS, deep and high-resolution images from HSC are available, in addition to X-ray fluxes from eROSITA and high S/N optical spectra from SDSS. These ancillary data are used to study the structural and environmental signatures, to discriminate between different formation scenarios, and to link local OMBHs to the extreme systems observed at high redshift. In my talk, I will present the results of morphological and environmental analyses aimed at understanding how these properties relate to the evolution of the host galaxies.