From the Circumnuclear Disk in the Galactic Center to thick, obscuring tori of AGNs

Abstract

The high accretion rates needed to fuel the central black hole in a galaxy can be achieved via viscous torques in thick disks and rings, which can be resolved by millimeter interferometry within the inner ∼20 pc of the active galaxy NGC 1068 at comparable scales and sensitivity to single dish observations of the Circumnuclear Disk (CND) in the Galactic Center. To interpret observations of these regions and determine the physical properties of their gas distribution, we present a modeling effort that includes the following: (i) simple dynamical simulations involving partially inelastic collisions between disk gas clouds; (ii) an analytical model of a turbulent clumpy gas disk calibrated by the dynamical model and observations; (iii) local turbulent and cosmic ray gas heating and cooling via H2O, H2, and CO emission; and (iv) determination of the molecular abundances. We also consider photodissociation regions (PDRs) where gas is directly illuminated by the central engine. We compare the resulting model datacubes of the CO, HCN, HCO+, and CS brightness temperatures to available observations. In both cases the kinematics can be explained by one or two clouds colliding with a preexisting ring, in a prograde sense for the CND and retrograde for NGC 1068. And, with only dense disk clouds, the line fluxes can be reproduced to within a factor of about two. To avoid self-absorption of the intercloud medium, turbulent heating at the largest scales, comparable to the disk height, has to be decreased by a factor of 50–200. Our models indicate that turbulent mechanical energy input is the dominant gas-heating mechanism within the thick gas disks. Turbulence is maintained by the gain of potential energy via radial gas accretion, which is itself enhanced by the collision of the infalling cloud. In NGC 1068, we cannot exclude that intercloud gas significantly contributes to the molecular line emission. In this object, while the bulk of the X-ray radiation of the active galactic nucleus is absorbed in a layer of Compton-thick gas inside the dust sublimation radius, the optical and UV radiation may enhance the molecular line emission from photodissociation regions by ∼50% at the inner edge of the gas ring. Infrared pumping may also increase the HCN(3−2) line flux throughout the gas ring by about a factor of two. Our models support the scenario of infalling gas clouds onto preexisting gas rings in galactic centers, and it is viable and consistent with available observations of the CND in the Galactic Center and the dense gas distribution within the inner 20 pc of NGC 1068.

The Evaporating Massive Embedded Stellar Cluster IRS 13 Close to Sgr A*. II. Kinematic Structure

“…However, we note that these parameters undergo a multidimensional transformation because not only will the velocity dispersion 〈v 2 〉 differ for the single objects inside of the cluster depending on their global habitat (CND and inner parsec), but also the impact parameter Λ will change due to the ongoing dissolution of IRS 13. In addition, the number density between the CND and inner parsec increases by almost 100% (Vollmer et al 2022) which should result in a decreased orbital energy (Zajaček et al 2017), which we mimic by setting v virial to 10% as soon as the cluster enters the NSC. Based on these settings, we show in Figure 7 the snapshots for a cluster with different numbers of particles moving toward the inner parsec at 0.1 Myr and 0.2 Myr.…”

Hydrodynamic simulations of the disc of gas around supermassive black holes (HDGAS) – I. Molecular gas dynamics

“…For instance, Shin et al ( 2021 ) showed that although NGC 1068 is known to have gas outflows originating from its AGN, more complex kinematical signatures have recently been detected that are in conflict with rotating outflows or simple biconical outflows. Vollmer et al ( 2022 ) applied the analytical model of a turbulent clumpy gas disc of Vollmer & Davies ( 2013 ) to produce an NGC 1068 dynamical model that could reproduce the high spatial resolution ALMA CO, HCO + , and HCN observations of the nucleus of NGC 1068. They find that the simplest configuration that can explain the kinematics of NGC 1068 is that of infalling gas clouds into a pre-existing gas ring and that the best-fitting cloud-ring collision is prograde for the CND and retrograde for the NGC 1068.…”