Massive molecular gas flows in the Abell 1664 brightest cluster galaxy

TL;DR

This study uses ALMA observations to reveal massive, complex molecular gas flows in the brightest cluster galaxy of Abell 1664, showing potential inflows and outflows with implications for galaxy evolution.

Contribution

First detailed ALMA analysis of molecular gas dynamics in Abell 1664's BCG, identifying high-velocity flows and asymmetric structures.

Findings

1. Molecular gas mass of 1.1x10^{10} solar masses divided into two velocity systems.

2. Evidence of a possible inflow or settling disk with asymmetric velocity structure.

3. Detection of high velocity gas clumps possibly indicating AGN-driven outflows.

Abstract

We report ALMA Early Science CO(1-0) and CO(3-2) observations of the brightest cluster galaxy (BCG) in Abell 1664. The BCG contains 1.1x10^{10} solar masses of molecular gas divided roughly equally between two distinct velocity systems: one from -250 to +250 km/s centred on the BCG's systemic velocity and a high velocity system blueshifted by 570 km/s with respect to the systemic velocity. The BCG's systemic component shows a smooth velocity gradient across the BCG center with velocity proportional to radius suggestive of solid body rotation about the nucleus. However, the mass and velocity structure are highly asymmetric and there is little star formation coincident with a putative disk. It may be an inflow of gas that will settle into a disk over several 10^8 yr. The high velocity system consists of two gas clumps, each ~2 kpc across, located to the north and southeast of the nucleus. Each has a line of sight velocity spread of 250-300 km/s. The velocity of the gas in the high velocity system tends to increase towards the BCG center and could signify a massive high velocity flow onto the nucleus. However, the velocity gradient is not smooth and these structures are also coincident with low optical-UV surface brightness regions, which could indicate dust extinction associated with each clump. If so, the high velocity gas would be projected in front of the BCG and moving toward us along the line of sight in a massive outflow most likely driven by the AGN. A merger origin is unlikely but cannot be ruled out.