Bob Armstrong

University of Illinois, Urbana-Champaign, Urbana, IL, United States

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Publications (4)5.99 Total impact

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    ABSTRACT: We present results of X-ray observations of a sample of 15 clusters selected via their imprint on the cosmic microwave background from the thermal Sunyaev-Zel'dovich (SZ) effect. These clusters are a subset of the first SZ-selected cluster catalog, obtained from observations of 178 deg2 of sky surveyed by the South Pole Telescope (SPT). Using X-ray observations with Chandra and XMM-Newton, we estimate the temperature, TX , and mass, Mg , of the intracluster medium within r 500 for each cluster. From these, we calculate YX = MgTX and estimate the total cluster mass using an M 500-YX scaling relation measured from previous X-ray studies. The integrated Comptonization, Y SZ, is derived from the SZ measurements, using additional information from the X-ray-measured gas density profiles and a universal temperature profile. We calculate scaling relations between the X-ray and SZ observables and find results generally consistent with other measurements and the expectations from simple self-similar behavior. Specifically, we fit a Y SZ-YX relation and find a normalization of 0.82 ± 0.07, marginally consistent with the predicted ratio of Y SZ/YX = 0.91 ± 0.01 that would be expected from the density and temperature models used in this work. Using the YX -derived mass estimates, we fit a Y SZ-M 500 relation and find a slope consistent with the self-similar expectation of Y SZM 5/3 with a normalization consistent with predictions from other X-ray studies. We find that the SZ mass estimates, derived from cosmological simulations of the SPT survey, are lower by a factor of 0.78 ± 0.06 relative to the X-ray mass estimates. This offset is at a level of 1.3σ when considering the ~15% systematic uncertainty for the simulation-based SZ masses. Overall, the X-ray measurements confirm that the scaling relations of the SZ-selected clusters are consistent with the properties of other X-ray-selected samples of massive clusters, even allowing for the broad redshift range (0.29 < z < 1.08) of the sample.
    Full-text · Article · Aug 2011 · The Astrophysical Journal
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    ABSTRACT: The Dark Energy Survey Data Management System (DESDM) will process and archive the data for the Dark Energy Survey (DES), a 5000 deg2 grizY survey on the Blanco 4-m telescope at Cerro Tololo Inter-American Observatory (CTIO). The goal of DES is to study dark energy using various techniques including galaxy clusters, supernova, large-scale structure and weak lensing. The DESDM system is responsible for calibrating the images and has been tested on simulated data from Fermilab and observed data from the Blanco Cosmology Survey (BCS), a 45 night NOAO survey. We will present results of photometric calibrations for both simulated and BCS data that incorporate the uniformity of the stellar locus in color-color space. The potential use of the stellar locus will be explored in the context of upcoming large surveys.
    No preview · Article · Jan 2010
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    ABSTRACT: The Dark Energy Survey (DES) collaboration is a multi-national science effort to understand cosmic acceleration and the nature of 'dark energy' responsible for this phenomenon. Dark Energy Survey Data Management (DESDM) system is a new observational astronomy processing pipeline and data management system that will be used to: process raw images obtained from a survey with the new DES field camera (DECam) covering 5000 sq degree of southern sky; archive intermediate and final co-added images; extract catalogs of celestial objects from every image and deliver data products to the astronomy community through portals and services. DESDM has been designed as a data intensive Science Gateway coupling use of shared computational resources (e.g. Teragrid) with project-owned databases and file systems for storage distributed across three continents. DESDM system over the next six years time will perform over 10 million CPU-hours (SUs) of image processing and serve over 4 Petabytes of images and 14 billion cataloged objects to the international DES collaboration. When delivered for operations in 2011, it will be one of, if not the, most scalable and powerful systems for processing telescope images, creating co-added deep images, and generating detailed star and galaxy catalogs in existence. The project's software components consist of a processing framework, an ensemble of astronomy codes, an integrated archive, a data-access framework and a portal infrastructure. This paper provides an overview of the DESDM scope and highlights, the architectural features developed and planned to be able to support Gateway-style management peta-scale intensive continuous processing and on-demand user queries for analysis.
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    ABSTRACT: We present results of X-ray observations of a sample of 15 clusters selected via their imprint on the cosmic microwave background (CMB) from the thermal Sunyaev-Zel'dovich (SZ) effect. These clusters are a subset of the first SZ-selected cluster catalog, obtained from observations of 178 deg^2 of sky surveyed by the South Pole Telescope. Using X-ray observations with Chandra and XMM-Newton, we estimate the temperature, T_X, and mass, M_g, of the intracluster medium (ICM) within r_500 for each cluster. From these, we calculate Y_X=M_g T_X and estimate the total cluster mass using a M_500-Y_X scaling relation measured from previous X-ray studies. The integrated Comptonization, Y_SZ, is derived from the SZ measurements, using additional information from the X-ray measured gas density profiles and a universal temperature profile. We calculate scaling relations between the X-ray and SZ observables, and find results generally consistent with other measurements and the expectations from simple self-similar behavior. Specifically, we fit a Y_SZ-Y_X relation and find a normalization of 0.82 +- 0.07, marginally consistent with the predicted ratio of Y_SZ/Y_X=0.91+-0.01 that would be expected from the density and temperature models used in this work. Using the Y_X derived mass estimates, we fit a Y_SZ-M_500 relation and find a slope consistent with the self-similar expectation of Y_SZ ~ M^5/3 with a normalization consistent with predictions from other X-ray studies. We compare the X-ray mass estimates to previously published SZ mass estimates derived from cosmological simulations of the SPT survey. We find that the SZ mass estimates are lower by a factor of 0.89+-0.06, which is within the ~15% systematic uncertainty quoted for the simulation-based SZ masses.
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