Molecular gas filaments and star-forming knots beneath an X-ray cavity in RXC J1504-0248

TL;DR

This study uses ALMA observations to analyze molecular gas filaments and star formation in the brightest cluster galaxy of RXC J1504-0248, revealing complex gas morphology, AGN-stimulated condensation, and ongoing star formation.

Contribution

First detailed ALMA analysis of molecular gas and star formation in RXC J1504.1$-$0248, linking gas morphology to AGN activity and star formation processes.

Findings

Molecular gas mass is $1.9×10^{10} M_{ ext{sun}}$ with complex, disturbed morphology.

A 20 kpc filament is aligned with an X-ray cavity, indicating AGN-stimulated condensation.

Star formation follows the Kennicutt-Schmidt law, with increased surface densities in the filament.

Abstract

We present recent ALMA observations of the CO(1-0) and CO(3-2) emission lines in the brightest cluster galaxy of RXCJ1504.1$-$0248, which is one of the most extreme cool core clusters known. The central galaxy contains $1.9\times 10^{10}~M_{\odot}$ of molecular gas. The molecular gas morphology is complex and disturbed, showing no evidence for a rotationally-supported structure in equilibrium. $80\%$ of the gas is situated within the central 5 kpc of the galactic center, while the remaining gas is located in a 20 kpc long filament. The cold gas has likely condensed out of the hot atmosphere. The filament is oriented along the edge of a putative X-ray cavity, suggesting that AGN activity has stimulated condensation. This is enegetically feasible, although the morphology is not as conclusive as systems whose molecular filaments trail directly behind buoyant radio bubbles. The velocity gradient along the filament is smooth and shallow. It is only consistent with free-fall if it lies within $20^{\circ}$ of the plane of the sky. The abundance of clusters with comparably low velocities suggests that the filament is not free-falling. Both the central and filamentary gas are coincident with bright UV emission from ongoing star formation. Star formation near the cluster core is consistent with the Kennicutt-Schmidt law. The filament exhibits increased star formation surface densities, possibly resulting from either the consumption of a finite molecular gas supply or spatial variations in the CO-to-H$_2$ conversion factor.