Speaker
Description
Active galactic nuclei (AGN) are powered by the accretion of material onto a supermassive black hole (SMBH) but the structure of this flow is not well understood. Standard accretion disc models match only to zeroth order in predicting the substantial energy dissipated in optically-thick material producing a strong blue/UV continuum. More detailed comparisons to the observed spectral shapes fail along with the ability to produce their variable nature. Based on stellar mass black holes in our own galaxy, the accretion disc should transition into an X-ray hot, radiatively inefficient flow below a (mass scaled) luminosity of 0.02Ledd. However, this is difficult to disentangle from increased dust obscuration and/or host galaxy contamination drowning out the AGN emission for the majority of the AGN population out to z~1. Here we use the new eROSITA eFEDS Survey to identify unobscured AGN from their X-ray emission, matched to excellent optical imaging from Subaru’s Hyper Suprime-Cam to subtract out the host galaxy contamination. The resulting spectra clearly show the shape of the distorted disc emission in bright AGN, and demonstrate that there is an intrinsic drop in this disc continuum below 0.02Ledd, revealing fundamental aspects of accretion physics in AGN.
