Jet-torus interaction revealed by sub-parsec SO absorption in NGC 1052

TL;DR

This study uses VLBI observations to detect SO absorption near the SMBH in NGC 1052, revealing jet-torus interactions and potential maser excitation, with implications for understanding AGN environments.

Contribution

First VLBI detection of broad SO absorption in NGC 1052, linking jet-torus interaction to molecular gas excitation and dynamics near the SMBH.

Findings

SO absorption confined within 0.45 pc of SMBH

Detection of redshifted and blueshifted SO components

Partial spatial and velocity correlation with H2O masers

Abstract

We report the first {\lambda}2-mm very long baseline interferometry (VLBI) observations of the radio galaxy NGC 1052, conducted with the Korean VLBI Network (KVN) using a wide-band recording mode. Leveraging the wide bandwidth covering a velocity range at 2300 km/s, we successfully detect broad (> 700 km/s) multi-component SO J_N = 3_3 - 2_2 absorption against the sub-parsec-scale continuum structure. The absorption profile consists of both redshifted and blueshifted components, including a newly identified blueshifted feature at -412 km/s relative to the systemic velocity. Significant SO absorption is confined to the central components, with no substantial detection toward the outer jet components. This constrains the location of SO gas to a compact region smaller than 0.45 pc in the sub-parsec vicinity of the supermassive black hole (SMBH). Our results support the scenario in which SO molecules are evaporated through shock heating caused by jet-torus interaction. The SO gas clumps are likely driven outward by the jet, with some returning toward the SMBH as inflowing material. Comparison with 321 GHz H2O masers reveals partial similarities in spatial distribution and radial velocity, suggesting that the jet-torus interaction may also trigger the excitation of H2O masers.