Computational modeling of dusty nuclear starburst disks and its consequences on observables

Abstract

Active galactic nuclei (AGNs) are the most energetic non-explosive objects in the uni- verse whose comoving space density peaks near redshift z ∼ 2 (Wolf et al., 2003). They radiate energy across the electromagnetic spectrum from radio to gamma rays. The number density of AGNs and their luminosity function with redshift play a key role in the evolution of massive black holes. They can also provide a feedback mechanism that can regulate galaxy growth, thus playing an important role in galaxy formation and their evolutionary models. However, the study of AGNs can be extremely complicated. There are numerous AGN classes dependent on physical characteristics such as luminosity, amount of obscuration, and observed emission lines. Many AGNs are observed to be obscured by dust and gas (Alexander & Hickox, 2012; LaMassa et al., 2017). The geometrical and physical conditions of these regions are not well understood. Moreover, obscured AGNs play an important role in explaining the cosmic X-ray background (Gilli et al., 2007; Akylas et al., 2012). Dusty nuclear starburst disks (NSDs) could potentially obscure the AGN in Seyfert galaxies (Ballantyne, 2008). I worked on testing this hypothesis by modeling the two-dimensional structure of NSDs. Since these disks are dusty, the atmosphere of a disk can be expanded when the dust sublimates near mid-plane. The expanded dusty atmosphere (near the surface) can then be supported by stellar radiation pressure (Thompson et al., 2005). NSDs could be a key to understanding the relation among the observed AGN obscuration, cosmic X-ray background, and star-forming regions at intermediate redshift.