Astronomy and Astrophysics, volume 521, A64-64 (2010/10-1)
The evolution of cool-core clusters.
SANTOS J.S., TOZZI P., ROSATI P. and BOEHRINGER H.
Abstract (from CDS):
Cool-core clusters are characterized by strong surface brightness peaks in the X-ray emission from the Intra Cluster Medium (ICM). This phenomenon is associated with complex physics in the ICM and has been a subject of intense debate and investigation in recent years. The evolution of cool-cores is still poorly constrained because of the small sample statistics and the observational challenge of analysing high redshift clusters. In order to quantify the evolution in the cool-core cluster population, we robustly measure the cool-core strength in a local, representative cluster sample, and in the largest sample of high-redshift clusters available to date. We use high-resolution Chandra data of three representative cluster samples spanning different redshift ranges: (i) the low redshift sample from the 400 Square degree (SD) survey with median <z≥0.08; (ii) the high redshift sample from the 400 SD Survey with median <z≥0.59; and (iii) 15 clusters drawn from the Rosat Distant Cluster Survey and the Wide Angle Rosat Pointed Survey, with median <z≥0.83. Our analysis is based on the measurement of the surface brightness concentration, cSB
(Santos et al., 2008A&A...483...35S
), which allows us to characterize the cool-core strength in low signal-to-noise data. We also obtain gas density profiles to derive cluster central cooling times and entropy. In addition to the X-ray analysis, we search for radio counterparts associated with the cluster cores. We find a statistically significant difference in the cSB
distributions of the two high-z samples, pointing towards a lack of concentrated clusters in the 400 SD high-z sample. Taking this into account, we confirm a negative evolution in the fraction of cool-core clusters with redshift, in particular for very strong cool-cores. This result is validated by the central entropy and central cooling time, which show strong anti-correlations with cSB
. However, the amount of evolution is significantly smaller than previously claimed, leaving room for a large population of well formed cool-cores at z∼1. Finally, we explore the potential of the proposed X-ray mission Wide Field X-ray Telescope to detect and quantify cool-cores up to z=1.5.
X-rays: galaxies: clusters - galaxies: clusters: interacluster medium, galaxies: high-redshift
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