The Redshift Evolution of the Mean Temperature, Pressure, and Entropy Profiles in 80 Spt-selected Galaxy Clusters

We present the results of an X-ray analysis of 80 galaxy clusters selected in the 2500 deg South Pole Telescope survey and observed with the Chandra X-ray Observatory. We divide the full sample into subsamples of ∼20 clusters based on redshift and central density, performing a joint X-ray spectral fit to all clusters in a subsample simultaneously, assuming self-similarity of the temperature profile. This approach allows us to constrain the shape of the temperature profile over 0 < r < 1.5R500, which would be impossible on a per-cluster basis, since the observations of individual clusters have, on average, 2000 X-ray counts. The results presented here represent the first constraints on the evolution of the average temperature profile from z = 0 to z = 1.2. We find that high-z (0.6 < z < 1.2) clusters are slightly (∼30%) cooler both in the inner (r < 0.1R500) and outer (r > R500) regions than their low-z (0.3 < z < 0.6) counterparts. Combining the average temperature profile with measured gas density profiles from our earlier work, we infer the average pressure and entropy profiles for each subsample. Confirming earlier results from this data set, we find an absence of strong cool cores at high z, manifested in this analysis as a significantly lower observed pressure in the central 0.1R500 of the high-z cool-core subset of clusters compared to the low-z cool-core subset. Overall, our observed pressure profiles agree well with earlier lower-redshift measurements, suggesting minimal redshift evolution in the pressure profile outside of the core. We find no measurable redshift evolution in the entropy profile at r . 0.7R500 – this may reflect a long-standing balance between cooling and feedback over long timescales and large physical scales. We observe a slight flattening of the entropy profile at r & R500 in our high-z subsample. This flattening is consistent with a temperature bias due to the enhanced (∼3×) rate at which group-mass (∼2 keV) halos, which would go undetected at our survey depth, are accreting onto the cluster at z ∼ 1. This work demonstrates a powerful method for inferring spatially-resolved cluster properties in the case where individual cluster signal-to-noise is low, but the number of observed clusters is high. Subject headings: galaxies: clusters: general – galaxies: clusters: intracluster medium – cosmology: early universe – X-rays: galaxies: clusters Email: [email protected] † Hubble Fellow 1 Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 2 Fermi National Accelerator Laboratory, Batavia, IL 605100500 3 Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 4 Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 6 University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 7 Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 452 Lomita Mall, Stanford, CA 94305 8 Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305 9 SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 10 Department of Physics, Harvard University, 17 Oxford Street, Cambridge, MA 02138 15 Department of Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 11 Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL, USA 60439 12 Department of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 München, Germany 13 Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany 14 Department of Physics and Astronomy, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110 16 Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 17 NIST Quantum Devices Group, 325 Broadway Mailcode 817.03, Boulder, CO, USA 80305 18 Departamento de Astronomia y Astrosifica, Pontificia Universidad Catolica, Chile 19 California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 20 Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8, Canada 21 Astronomy Department, University of Illinois at Urbana-