2025-03-07 Abstract
Title: The Evolution and Mechanism of Obscuration in Active Galactic Nuclei at Cosmic Noon
Speaker: Bovornpratch Klod Vijarnwannaluk (ASIAA)
Date: March 7 at 14:30
Location: R521, General Building II
Abstract:
Active galactic nuclei (AGN) are supermassive black holes (SMBH) that are undergoing mass accretion, Statistical X-ray AGN studies show that the majority of active galactic nuclei (AGN) show large amounts of absorption in their X-ray emission indicating that most accretion occurs behind heavy obscuration. The fraction of absorbed AGN also shows an increase with redshift and a decrease with luminosity. Using the uniquely deep & wide multiwavelength imaging datasets in the HSC-Deep XMM-LSS field, we estimated the absorbed fraction of luminous AGN with log Lx [erg /s]>44.5 above redshift 2 is 76±4% which is more than twice the fraction in the local universe (~30%). We further investigated obscuration properties of Type 1 & 2 AGN at redshift 0.8-1.8 by investigating their distribution of the Hydrogen column density and Eddington ratio diagram. We show that the Eddington ratio of Type-2 AGN is lower than type-1 broad-line AGN consistent with obscuration due to a radiation pressure-regulated dusty torus. However, we find evidence of non-nuclear obscuration among the sample of Type-1 AGN and Type-2 AGN. These observations indicate that obscuration in high redshift black hole growth is not solely due to nuclear obscuration by a dusty torus. It requires additional components of obscuration from the host galaxy as well as dust-free absorption by nuclear gas. Lastly, we discuss the possibility of investigating the obscuration due to the host galaxy interstellar medium among high redshift AGN using JWST and mm observations.