Circumnuclear Medium around the Central AGN in a Cool-Core Cluster, Abell 1644-South

TL;DR

This study investigates the multi-phase gas around the central AGN in Abell 1644-South, revealing cold gas inflows likely triggered by ICM cooling, which may fuel AGN activity in a cool-core cluster.

Contribution

It provides the first detailed multi-wavelength analysis of the circumnuclear gas in A1644-S, linking cold gas dynamics with AGN fueling in a merging cool-core cluster.

Findings

CO clumps form an arc along X-ray sloshing, indicating interaction with hot ICM.

HI and CN absorption features suggest gas spirals into the BCG core.

Detection of a parsec-scale bipolar jet implies recent AGN activity.

Abstract

We present the circumnuclear multi-phase gas properties of the brightest cluster galaxy (BCG) in the center of Abell 1644-South. A1644-S is the main cluster in a merging system, which is well known for X-ray hot gas sloshing in its core. The sharply peaked X-ray profile of A1644-S implies the presence of a strongly cooling gas core. In this study, we analyze ALMA CO (1-0) data, JVLA HI data, and KaVA 22 GHz data for the central region of A1644-S to probe the potential origin of the cool gas and its role in (re)powering the central active galactic nucleus (AGN). We find CO clumps distributed in an arc shape along the X-ray gas sloshing, which is suggestive of a connection between the cold gas and the hot intracluster medium (ICM). HI and CN are detected in absorption against the AGN continuum emission. The absorption dip is observed at the systemic velocity of the BCG with an extended, redshifted tail. Based on the spatial and spectral configurations of the HI, CN and CO gases, it is inferred that cool gas spirals into the core of the BCG, which is then fed to the central AGN. Indeed, our KaVA observation reveals a parsec-scale bipolar jet, implying that this AGN could have been (re)powered quite recently. Combining this, we suggest that some cold gas in A1644-S could have been formed from the cooling of the ICM, triggering the activity of the central AGN in the early development of a cool-core cluster.