Molecular Gas Filaments and Star-forming Knots Beneath an X-Ray Cavity in RXC J1504–0248

Abstract

We present recent ALMA observations of the CO (1-0) and CO (3-2) emission lines in the brightest cluster galaxy of RXC J1504.1-0248, which is one of the most extreme cool core clusters known. The central galaxy contains 1.9 - 1010 M⊙ of molecular gas. The molecular gas morphology is complex and disturbed, showing no evidence for a rotationally supported structure in equilibrium. A total of 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 active galactic nucleus activity has stimulated condensation. This is energetically 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 freefall if it lies within 20- of the plane of the sky. The abundance of clusters with comparably low velocities suggests that the filament is not freefalling. Both the central gas 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-H2 conversion factor.