# Disentangling the Circumnuclear Environs of Centaurus A: III. An Inner Molecular Ring, Nuclear Shocks and the CO to warm H2 interface

## TL;DR

This study uses high-resolution ALMA observations to analyze the molecular gas structures and dynamics in Centaurus A's circumnuclear disk, revealing a ring, filamentary shocks, and spiral features that likely facilitate AGN feeding.

## Contribution

It provides detailed insights into the molecular gas morphology and kinematics at parsec scales, highlighting the role of shocks and non-circular motions in AGN fueling, which is a novel high-resolution analysis of Centaurus A.

## Key findings

- Identification of a 162x108 pc molecular ring structure.
- Detection of nuclear shocks and filamentary inflows.
- Evidence of non-circular motions facilitating angular momentum loss.

## Abstract

We present the distribution and kinematics of the molecular gas in the circumnuclear disk (CND, 400 pc x 200 pc) of Centaurus A with resolutions of ~5 pc (0.3 arcsec) and shed light onto the mechanism feeding the Active Galactic Nucleus (AGN) using CO(3-2), HCO+(4-3), HCN(4-3), and CO(6-5) observations obtained with ALMA. Multiple filaments or streamers of tens to a hundred parsec scale exist within the CND, which form a ring-like structure with an unprojected diameter of 9 x 6 arcsec (162pc x 108pc) and a position angle PA = 155deg. Inside the nuclear ring, there are two leading and straight filamentary structures with lengths of about 30-60pc at PA = 120deg on opposite sides of the AGN, with a rotational symmetry of 180deg and steeper position-velocity diagrams, which are interpreted as nuclear shocks due to non-circular motions. Along the filaments, and unlike other nearby AGNs, several dense molecular clumps present low HCN/HCO+(4-3) ratios (~0.5). The filaments abruptly end in the probed transitions at r = 20pc from the AGN, but previous near-IR H2 (J=1-0) S(1) maps show that they continue in an even ~1000 K), winding up in the form of nuclear spirals, and forming an inner ring structure with another set of symmetric filaments along the N-S direction and within r = 10pc. The molecular gas is governed primarily by non-circular motions, being the successive shock fronts at different scales where loss of angular momentum occurs, a mechanism which may feed efficiently powerful radio galaxies down to parsec scales.