A Chandra X-ray Analysis of Abell 1664: Cooling, Feedback and Star Formation in the Central Cluster Galaxy

TL;DR

This study analyzes the cooling, feedback, and star formation processes in the central galaxy of Abell 1664 using Chandra X-ray data, revealing rapid cooling and a low-activity AGN phase.

Contribution

It provides new insights into the cooling flow, metallicity distribution, and AGN feedback cycle in Abell 1664's central galaxy, supported by detailed X-ray analysis.

Findings

The BCG is actively forming stars at ~23 solar masses per year.

The X-ray and molecular gas masses are comparable, indicating in-situ gas condensation.

The AGN is underpowered relative to the cooling luminosity, suggesting a low-feedback state.

Abstract

The brightest cluster galaxy (BCG) in the Abell 1664 cluster is unusually blue and is forming stars at a rate of ~ 23 M_{\sun} yr^{-1}. The BCG is located within 5 kpc of the X-ray peak, where the cooling time of 3.5x10^8 yr and entropy of 10.4 keV cm^2 are consistent with other star-forming BCGs in cooling flow clusters. The center of A1664 has an elongated, "bar-like" X-ray structure whose mass is comparable to the mass of molecular hydrogen, ~ 10^{10} M_{\sun} in the BCG. We show that this gas is unlikely to have been stripped from interloping galaxies. The cooling rate in this region is roughly consistent with the star formation rate, suggesting that the hot gas is condensing onto the BCG. We use the scaling relations of Birzan et al. 2008 to show that the AGN is underpowered compared to the central X-ray cooling luminosity by roughly a factor of three. We suggest that A1664 is experiencing rapid cooling and star formation during a low-state of an AGN feedback cycle that regulates the rates of cooling and star formation. Modeling the emission as a single temperature plasma, we find that the metallicity peaks 100 kpc from the X-ray center, resulting in a central metallicity dip. However, a multi-temperature cooling flow model improves the fit to the X-ray emission and is able to recover the expected, centrally-peaked metallicity profile.