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

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 3.5 × 108 yr and entropy of 10.4 keV cm2 are consistent with other star-forming BCGs in cooling flow clusters. The center of A1664 has an elongated, “barlike” 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 Bırzan et al. to show that the active galactic nucleus (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.