THE GROWTH OF COOL CORES AND EVOLUTION OF COOLING PROPERTIES IN A SAMPLE OF 83 GALAXY CLUSTERS AT 0.3 <z< 1.2 SELECTED FROM THE SPT-SZ SURVEY

Abstract

We present first results on the cooling properties derived from Chandra X-ray observations of 83 high-redshift (0.3 < z < 1.2) massive galaxy clusters selected by their Sunyaev-Zel'dovich signature in the South Pole Telescope data. We measure each cluster's central cooling time, central entropy, and mass deposition rate, and compare these properties to those for local cluster samples. We find no significant evolution from z ∼ 0 to z ∼ 1 in the distribution of these properties, suggesting that cooling in cluster cores is stable over long periods of time. We also find that the average cool core entropy profile in the inner ∼100 kpc has not changed dramatically since z ∼ 1, implying that feedback must be providing nearly constant energy injection to maintain the observed "entropy floor" at ∼10 keV cm 2 . While the cooling properties appear roughly constant over long periods of time, we observe strong evolution in the gas density profile, with the normalized central density (ρ g,0 /ρ crit ) increasing by an order of magnitude from z ∼ 1 to z ∼ 0. When using metrics defined by the inner surface brightness profile of clusters, we find an apparent lack of classical, cuspy, cool-core clusters at z > 0.75, consistent with earlier reports for clusters at z > 0.5 using similar definitions. Our measurements indicate that cool cores have been steadily growing over the 8 Gyr spanned by our sample, consistent with a constant, ∼150 M yr −1 cooling flow that is unable to cool below entropies of 10 keV cm 2 and, instead, accumulates in the cluster center. We estimate that cool cores began to

STAR-FORMING BRIGHTEST CLUSTER GALAXIES AT 0.25 < z < 1.25: A TRANSITIONING FUEL SUPPLY

“…The sample is initially defined to include all 83 clusters from McDonald et al (2013b), which were selected from the SPT 2500 deg 2 survey (Bleem et al 2015) and subsequently observed in the X-ray with the Chandra X-ray Observatory. To this sample, we add an additional eight clusters from Bleem et al (2015) that have archival Chandra data from other sources (SPT-CLJ0106-5943, SPT-CLJ0232-4421, SPT-CLJ0235-5121, SPT-CLJ0516-5430, SPT-CLJ0522-4818, SPT-CLJ0658-5556, SPT-CLJ2011-5725, SPT-CLJ2332-5053).…”

“…The "central" density is computed based on the deprojected X-ray surface brightness profile, following Vikhlinin et al (2006) and McDonald et al (2013b). Because the measurement of electron density requires far fewer X-ray counts than the measurement of spectroscopic temperature, the central density is measured at r=0.01 R 500 , or roughly 10 kpc for a typical cluster in this sample.…”

“…Unlike our previous work (McDonald et al 2013b), here we measure "central" quantities at the X-ray peak, rather than the large-scale centroid. In general, the BCG is located closer to the X-ray peak than the centroid in cases of merging clusters, which motivated this choice.…”

“…Most recently, the completed 2500 deg 2 SZ survey with the South Pole Telescope (SPT; Carlstrom et al 2011) has discovered more than 500 massive galaxy clusters, the majority of which are at z>0.5 (Bleem et al 2015). In this work, we focus on a subsample of this survey that has been targeted for X-ray follow-up (McDonald et al 2013b) and spans a redshift range of 0.3<z<1.2. The availability of optical photometry and spectroscopy for the majority of the BCGs in this sample, along with archival UV (GALEX) and IR (WISE) data, allows us to study star formation in BCGs at high redshift for a complete, mass-selected sample.…”

An overview of jet-mode AGN feedback and the prospects for studying its cosmic evolution with LOFAR

“…For example, separations can be made using a temperature gradient criterion , the concentration parameter (Santos et al 2008;McDonald et al 2013), or the central cooling time or entropy (O' Hara et al 2006;Chen et al 2007;Pratt et al 2009;Cavagnolo et al 2009;Hudson et al 2010;McDonald et al 2013). For the latter criteria, the choice of cooling-time or entropy threshold and radius can give different results (for a review see Sun 2012).…”