The Clusters Hiding in Plain Sight (CHiPS) Survey: A First Discovery of a Massive Nearby Cluster around PKS 1353−341

Abstract

Abstract We introduce the first result of the Clusters Hiding in Plain Sight (CHiPS) survey, which aims to discover new nearby massive galaxy clusters that were incorrectly identified as isolated point sources in the ROSAT All-sky Survey. We present a Chandra X-ray observation of our first newly discovered low-redshift (z = 0.223) galaxy cluster with a central X-ray bright point source, PKS 1353−341. After removing the point source contribution to the cluster core (L nuc ∼ 1.8 × 1044 erg s−1), we determine various properties of the cluster. The presence of a relaxed X-ray morphology, a central temperature drop, and a central cooling time around 400 Myr indicates that it is a strong cool-core cluster. The central galaxy appears to be forming stars at the rate of 6.2 ± 3.6 M ⊙ yr−1, corresponding to ∼1% of the classical cooling prediction. The supermassive black hole in the central galaxy appears to be accreting at ∼0.1% of the Eddington rate with a total power output of ∼5 × 1045 erg s−1, split nearly equally between radiative and mechanical power. We see weak evidence of localized excess entropy at a radius of 200 kpc, which, if true, could imply a recent (∼180 Myr) energetic outburst in the core that has risen buoyantly to a larger radius. Comparing the cluster’s bulk properties with those of other known clusters (e.g., the total mass M 500 is , and the bolometric X-ray luminosity L X is 7 × 1044 erg s−1), we show that this cluster, which is massive enough that it was detected (but not confirmed) by the Planck survey, is also sufficiently luminous that it would have been identified as a cluster in the ROSAT All-sky Survey if it did not have such a bright central point source. This discovery demonstrates the potential of the CHiPS survey to find massive nearby clusters with extreme central properties that may have been missed or misidentified by previous surveys.