Ray-tracing GR-MHD-generated Outflows from AGNs Hosting Thin Accretion Disks: An Analysis Approaching Horizon Scales

TL;DR

This study uses resistive GR-MHD simulations of thin accretion disks around SMBHs to analyze near-horizon emission properties, revealing differences in optical thickness and outflow visibility relevant for EHT observations.

Contribution

It introduces a novel modeling approach of thin disk accretion and outflows near SMBHs, contrasting with traditional thick disk models, to better interpret horizon-scale observations.

Findings

Low-mass SMBHs appear optically thicker at 230 GHz.

Doppler beaming influences outflow brightness with viewing angle.

High-mass SMBHs show optically thinner emission, ideal for GR effects detection.

Abstract

AGNs exhibit a wide range of black hole masses and inflow/outflow properties. It is now possible to probe regions close to the event horizons of nearby SMBHs using VLBI with earth-sized baselines, as performed by the EHT. This study explores the emission properties of accretion and outflows near the event horizon of both low-mass and high-mass SMBHs. Using resistive GR-MHD simulations, we model AGNs with thin Keplerian disks. This contrasts with widely studied models featuring thick disks, such as magnetically arrested disks (MADs) or the standard and normal evolution (SANE) scenario. Our models serve as simplified representations to study disk-jet-wind structures. These simulations are postprocessed and ray-traced, using constraints of black hole mass and observed SEDs. Thermal synchrotron emission generated near the event horizon is used to create emission maps, which are analysed by separating accretion and outflow components to determine their contributions to the total intensity. Whether the emission appears optically thick or thin at a given frequency depends on its position relative to the synchrotron SED peak. At 230 GHz, low-mass SMBHs appear optically thicker than high-mass ones, even at lower accretion rates. Doppler beaming affects the brightness of emission from outflows with changing viewing angles in low-mass systems. Eddington ratios from our models align with those inferred by the EHTC for M87 and SgrA* using thicker MAD/SANE models. Although thin disks are optically thicker, their spectral properties make high-mass systems appear optically thinner at 230 GHz; ideal for probing GR effects like photon rings. In contrast, low-mass systems remain optically thicker at these frequencies because of synchrotron self-absorption, making outflow emissions near the horizon more pronounced. However, distinguishing these features remains challenging with current EHT resolution.