K. K. Schaffer

Publications (48)135.73 Total impact

• Article: 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

  M. McDonald, B. A. Benson, A. Vikhlinin, B. Stalder, L. E. Bleem, H. W. Lin, K. A. Aird, M. L. N. Ashby, M. W. Bautz, M. Bayliss, [......], S. A. Stanford, Z. Staniszewski, A. A. Stark, K. Story, A. van Engelen, K. Vanderlinde, J. D. Vieira, R. Williamson, O. Zahn, A. Zenteno
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  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 to 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 (rho_0/rho_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 Msun/yr 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 assemble in these massive systems at z ~ 1, which represents the first constraints on the onset of cooling in galaxy cluster cores. We investigate several potential biases which could conspire to mimic this cool core evolution and are unable to find a bias that has a similar redshift dependence and a substantial amplitude.
  05/2013;
• Article: Dusty starburst galaxies in the early Universe as revealed by gravitational lensing.

  J D Vieira, D P Marrone, S C Chapman, C De Breuck, Y D Hezaveh, A Weiβ, J E Aguirre, K A Aird, M Aravena, M L N Ashby, [......], L Shaw, E Shirokoff, J S Spilker, B Stalder, Z Staniszewski, A A Stark, K Story, K Vanderlinde, N Welikala, R Williamson
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  ABSTRACT: In the past decade, our understanding of galaxy evolution has been revolutionized by the discovery that luminous, dusty starburst galaxies were 1,000 times more abundant in the early Universe than at present. It has, however, been difficult to measure the complete redshift distribution of these objects, especially at the highest redshifts (z > 4). Here we report a redshift survey at a wavelength of three millimetres, targeting carbon monoxide line emission from the star-forming molecular gas in the direction of extraordinarily bright millimetre-wave-selected sources. High-resolution imaging demonstrates that these sources are strongly gravitationally lensed by foreground galaxies. We detect spectral lines in 23 out of 26 sources and multiple lines in 12 of those 23 sources, from which we obtain robust, unambiguous redshifts. At least 10 of the sources are found to lie at z > 4, indicating that the fraction of dusty starburst galaxies at high redshifts is greater than previously thought. Models of lens geometries in the sample indicate that the background objects are ultra-luminous infrared galaxies, powered by extreme bursts of star formation.
  Nature 03/2013; · 36.28 Impact Factor
• Article: ALMA Observations of SPT-Discovered, Strongly Lensed, Dusty, Star-Forming Galaxies

  Y. D. Hezaveh, D. P. Marrone, C. D. Fassnacht, J. S. Spilker, J. D. Vieira, J. E. Aguirre, K. A. Aird, M. Aravena, M. L. N. Ashby, M. Bayliss, [......], L. Shaw, E. Shirokoff, B. Stalder, Z. Staniszewski, A. A. Stark, K. Story, K. Vanderlinde, A. Weiß, N. Welikala, R. Williamson
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  ABSTRACT: We present Atacama Large Millimeter/submillimeter Array (ALMA) 860 micrometer imaging of four high-redshift (z=2.8-5.7) dusty sources that were detected using the South Pole Telescope (SPT) at 1.4 mm and are not seen in existing radio to far-infrared catalogs. At 1.5 arcsec resolution, the ALMA data reveal multiple images of each submillimeter source, separated by 1-3 arcsec, consistent with strong lensing by intervening galaxies visible in near-IR imaging of these sources. We describe a gravitational lens modeling procedure that operates on the measured visibilities and incorporates self-calibration-like antenna phase corrections as part of the model optimization, which we use to interpret the source structure. Lens models indicate that SPT0346-52, located at z=5.7, is one of the most luminous and intensely star-forming sources in the universe with a lensing corrected FIR luminosity of 3.7 X 10^13 L_sun and star formation surface density of 4200 M_sun yr^-1 kpc^-2. We find magnification factors of 5 to 22, with lens Einstein radii of 1.1-2.0 arcsec and Einstein enclosed masses of 1.6-7.2x10^11 M_sun. These observations confirm the lensing origin of these objects, allow us to measure the their intrinsic sizes and luminosities, and demonstrate the important role that ALMA will play in the interpretation of lensed submillimeter sources.
  03/2013;
• Article: Dusty starburst galaxies in the early Universe as revealed by gravitational lensing

  J. D. Vieira, D. P. Marrone, S. C. Chapman, C. De Breuck, Y. D. Hezaveh, A. Weiss, J. E. Aguirre, K. A. Aird, M. Aravena, M. L. N. Ashby, [......], K. K. Schaffer, L. Shaw, E. Shirokoff, J. S. Spilker, B. Stalder, A. A. Stark, K. Story, K. Vanderlinde, N. Welikala, R. Williamson
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  ABSTRACT: In the past decade, our understanding of galaxy evolution has been revolutionized by the discovery that luminous, dusty, starburst galaxies were 1,000 times more abundant in the early Universe than at present. It has, however, been difficult to measure the complete redshift 2 distribution of these objects, especially at the highest redshifts (z > 4). Here we report a redshift survey at a wavelength of three millimeters, targeting carbon monoxide line emission from the star-forming molecular gas in the direction of extraordinarily bright millimetrewave-selected sources. High-resolution imaging demonstrates that these sources are strongly gravitationally lensed by foreground galaxies. We detect spectral lines in 23 out of 26 sources and multiple lines in 12 of those 23 sources, from which we obtain robust, unambiguous redshifts. At least 10 of the sources are found to lie at z > 4, indicating that the fraction of dusty starburst galaxies at high redshifts is greater than previously thought. Models of lens geometries in the sample indicate that the background objects are ultra-luminous infrared galaxies, powered by extreme bursts of star formation.
  03/2013;
• Article: ALMA redshifts of millimeter-selected galaxies from the SPT survey: The redshift distribution of dusty star-forming galaxies

  A. Weiss, C. De Breuck, D. P. Marrone, J. D. Vieira, J. E. Aguirre, K. A. Aird, M. Aravena, M. L. N. Ashby, M. Bayliss, B. A. Benson, [......], K. K. Schaffer, E. Shirokoff, J. S. Spilker, B. Stalder, Z. Staniszewski, A. A. Stark, K. Story, K. Vanderlinde, N. Welikala, R. Williamson
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  ABSTRACT: Using the Atacama Large Millimeter/submillimeter Array (ALMA), we have conducted a blind redshift survey in the 3 mm atmospheric transmission window for 26 strongly lensd dusty star-forming galaxies (DSFGs) selected with the South Pole Telescope (SPT). The sources were selected to have S_1.4mm>20 mJy and a dust-like spectrum and, to remove low-z sources, not have bright radio (S_843MHz<6mJy) or far-infrared counterparts (S_100um<1 Jy, S_60um<200mJy). We robustly detect 44 line features in our survey, which we identify as redshifted emission lines of 12CO, 13CO, [CI], H2O, and H2O+. We find one or more spectral features in 23 sources yielding a ~90% detection rate for this survey; in 12 of these sources we detect multiple lines, while in 11 sources we detect only a single line. For the sources with only one detected line, we break the redshift degeneracy with additional spectroscopic observations if available, or infer the most likely line identification based on photometric data. This yields secure redshifts for ~70% of the sample. The three sources with no lines detected are tentatively placed in the redshift desert between 1.7<z<2.0. The resulting mean redshift of our sample is =3.5. This finding is in contrast to the redshift distribution of radio-identified DSFGs, which have a significantly lower mean redshift of =2.3 and for which only 10-15% of the population is expected to be at z>3. We discuss the effect of gravitational lensing on the redshift distribution and compare our measured redshift distribution to that of models in the literature.
  03/2013;
• Article: Constraints on Cosmology from the Cosmic Microwave Background Power Spectrum of the 2500-square degree SPT-SZ Survey

  Z. Hou, C. L. Reichardt, K. T. Story, B. Follin, R. Keisler, K. A. Aird, B. A. Benson, L. E. Bleem, J. E. Carlstrom, C. L. Chang, [......], L. Shaw, E. Shirokoff, H. G. Spieler, Z. Staniszewski, A. A. Stark, A. van Engelen, K. Vanderlinde, J. D. Vieira, R. Williamson, O. Zahn
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  ABSTRACT: We explore extensions to the standard LCDM cosmological model using new measurements of the cosmic microwave background (CMB) from the South Pole Telescope (SPT). Adding SPT measurements to WMAP7 significantly improves constraints on possible extensions to the LCDM model; the addition of low-redshift measurements of H0 and BAO leads to further improvements. Before combining these datasets, we check for consistency in the LCDM model between measurements of the CMB (SPT+WMAP7), H0 and BAO, and find evidence for some tension between the datasets. Within the CMB data alone, we find only weak support for physics beyond the LCDM model due to a slight trend of decreasing power at smaller angular scales, relative to the prediction of the LCDM model. This trend could be due to a logarithmic scale dependence of the power-law index of the primordial power spectrum, nrun. Alternatively, the trend could arise either from adjustments at small or large scales. The power at small scales is sensitive to the damping scale which is influenced by both the helium abundance, Yp and the effective number of neutrino species, Neff. The power at large scales is affected by the ISW effect which is sensitive to the sum of neutrino masses, mnu. These extensions have similar observational consequences and are partially degenerate when considered simultaneously. These degeneracies can weaken or enhance the apparent deviation of any single extension from the LCDM model. Of the 6 one-parameter model extensions considered, we find the CMB data to have the largest statistical preference for running within [-0.046, -0.003] at 95% confidence...[abridged]
  12/2012;
• Article: A Measurement of the Cosmic Microwave Background Damping Tail from the 2500-square-degree SPT-SZ survey

  K. T. Story, C. L. Reichardt, Z. Hou, R. Keisler, K. A. Aird, B. A. Benson, L. E. Bleem, J. E. Carlstrom, C. L. Chang, H-M. Cho, [......], L. Shaw, E. Shirokoff, H. G. Spieler, Z. Staniszewski, A. A. Stark, A. van Engelen, K. Vanderlinde, J. D. Vieira, R. Williamson, O. Zahn
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  ABSTRACT: We present a measurement of the cosmic microwave background (CMB) temperature power spectrum using data from the recently completed South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. This measurement is made from observations of 2540 deg^2 of sky with arcminute resolution at 150 GHz, and improves upon previous measurements using the SPT by tripling the sky area. We report CMB temperature anisotropy power over the multipole range 650<\ell<3000. We fit the SPT bandpowers, combined with the results from the seven-year Wilkinson Microwave Anisotropy Probe (WMAP7) data release, with a six-parameter LCDM cosmological model and find that the two datasets are consistent and well fit by the model. Adding SPT measurements significantly improves LCDM parameter constraints, and in particular tightens the constraint on the angular sound horizon \theta_s by a factor of 2.7. The impact of gravitational lensing on the CMB power spectrum is detected with 8.1 \sigma, the most significant detection to date. The inferred amplitude of the lensing spectrum is consistent with the LCDM prediction. This sensitivity of the SPT+WMAP7 data to lensing by large-scale structure at low redshifts allows us to constrain the mean curvature of the observable universe with CMB data alone to be \Omega_K=-0.003+0.014-0.018. Using the SPT+WMAP7 data, we measure the spectral index of scalar fluctuations to be ns=0.9623+/-0.0097 in the LCDM model, a 3.9 \sigma preference for a scale-dependent spectrum with ns<1. The SPT measurement of the CMB damping tail helps break the degeneracy that exists between the tensor-to-scalar ratio r and ns in large-scale CMB measurements, leading to an upper limit of r<0.18 (95% C.L.) in the LCDM+r model. Adding low-redshift measurements of the Hubble constant ($H_0$) and the baryon acoustic oscillation (BAO) feature ...[abridged]
  10/2012;
• Article: Design and characterization of 90 GHz feedhorn-coupled TES polarimeter pixels in the SPTpol camera

  J. T. Sayre, P. Ade, K. A. Aird, J. E. Austermann, J. A. Beall, D. Becker, B. A. Benson, L. E. Bleem, J. Britton, J. E. Carlstrom, [......], E. Shirokoff, K. Story, C. Tucker, K. Vanderlinde, J. D. Vieira, G. Wang, R. Williamson, V. Yefremenko, K. W. Yoon, E. Young
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  ABSTRACT: The SPTpol camera is a two-color, polarization-sensitive bolometer receiver, and was installed on the 10 meter South Pole Telescope in January 2012. SPTpol is designed to study the faint polarization signals in the Cosmic Microwave Background, with two primary scientific goals. One is to constrain the tensor-to-scalar ratio of perturbations in the primordial plasma, and thus constrain the space of permissible inflationary models. The other is to measure the weak lensing effect of large-scale structure on CMB polarization, which can be used to constrain the sum of neutrino masses as well as other growth-related parameters. The SPTpol focal plane consists of seven 84-element monolithic arrays of 150 GHz pixels (588 total) and 180 individual 90 GHz single-pixel modules. In this paper we present the design and characterization of the 90 GHz modules.
  10/2012;
• Article: South Pole Telescope Software Systems: Control, Monitoring, and Data Acquisition

  K. Story, E. Leitch, P. Ade, K. A. Aird, J. E. Austermann, J. A. Beall, D. Becker, A. N. Bender, B. A. Benson, L. E. Bleem, [......], G. Smecher, B. Stalder, C. Tucker, K. Vanderlinde, J. D. Vieira, G. Wang, R. Williamson, V. Yefremenko, K. W. Yoon, E. Young
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  ABSTRACT: We present the software system used to control and operate the South Pole Telescope. The South Pole Telescope is a 10-meter millimeter-wavelength telescope designed to measure anisotropies in the cosmic microwave background (CMB) at arcminute angular resolution. In the austral summer of 2011/12, the SPT was equipped with a new polarization-sensitive camera, which consists of 1536 transition-edge sensor bolometers. The bolometers are read out using 36 independent digital frequency multiplexing (\dfmux) readout boards, each with its own embedded processors. These autonomous boards control and read out data from the focal plane with on-board software and firmware. An overall control software system running on a separate control computer controls the \dfmux boards, the cryostat and all other aspects of telescope operation. This control software collects and monitors data in real-time, and stores the data to disk for transfer to the United States for analysis.
  10/2012;
• Article: Feedhorn-coupled TES polarimeter camera modules at 150 GHz for CMB polarization measurements with SPTpol

  J. W. Henning, P. Ade, K. A. Aird, J. E. Austermann, J. A. Beall, D. Becker, B. A. Benson, L. E. Bleem, J. Britton, J. E. Carlstrom, [......], E. Shirokoff, K. Story, C. Tucker, K. Vanderlinde, J. D. Vieira, G. Wang, R. Williamson, V. Yefremenko, K. W. Yoon, E. Young
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  ABSTRACT: The SPTpol camera is a dichroic polarimetric receiver at 90 and 150 GHz. Deployed in January 2012 on the South Pole Telescope (SPT), SPTpol is looking for faint polarization signals in the Cosmic Microwave Background (CMB). The camera consists of 180 individual Transition Edge Sensor (TES) polarimeters at 90 GHz and seven 84-polarimeter camera modules (a total of 588 polarimeters) at 150 GHz. We present the design, dark characterization, and in-lab optical properties of the 150 GHz camera modules. The modules consist of photolithographed arrays of TES polarimeters coupled to silicon platelet arrays of corrugated feedhorns, both of which are fabricated at NIST-Boulder. In addition to mounting hardware and RF shielding, each module also contains a set of passive readout electronics for digital frequency-domain multiplexing. A single module, therefore, is fully functional as a miniature focal plane and can be tested independently. Across the modules tested before deployment, the detectors average a critical temperature of 478 mK, normal resistance R_N of 1.2 Ohm, unloaded saturation power of 22.5 pW, (detector-only) optical efficiency of ~ 90%, and have electrothermal time constants < 1 ms in transition.
  10/2012;
• Article: SPTpol: an instrument for CMB polarization measurements with the South Pole Telescope

  J. E. Austermann, K. A. Aird, J. A. Beall, D. Becker, A. Bender, B. A. Benson, L. E. Bleem, J. Britton, J. E. Carlstrom, C. L. Chang, [......], E. Shirokoff, A. A. Stark, K. Story, K. Vanderlinde, J. D. Vieira, G. Wang, R. Williamson, V. Yefremenko, K. W. Yoon, O. Zahn
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  ABSTRACT: SPTpol is a dual-frequency polarization-sensitive camera that was deployed on the 10-meter South Pole Telescope in January 2012. SPTpol will measure the polarization anisotropy of the cosmic microwave background (CMB) on angular scales spanning an arcminute to several degrees. The polarization sensitivity of SPTpol will enable a detection of the CMB "B-mode" polarization from the detection of the gravitational lensing of the CMB by large scale structure, and a detection or improved upper limit on a primordial signal due to inflationary gravity waves. The two measurements can be used to constrain the sum of the neutrino masses and the energy scale of inflation. These science goals can be achieved through the polarization sensitivity of the SPTpol camera and careful control of systematics. The SPTpol camera consists of 768 pixels, each containing two transition-edge sensor (TES) bolometers coupled to orthogonal polarizations, and a total of 1536 bolometers. The pixels are sensitive to light in one of two frequency bands centered at 90 and 150 GHz, with 180 pixels at 90 GHz and 588 pixels at 150 GHz. The SPTpol design has several features designed to control polarization systematics, including: single-moded feedhorns with low cross-polarization, bolometer pairs well-matched to difference atmospheric signals, an improved ground shield design based on far-sidelobe measurements of the SPT, and a small beam to reduce temperature to polarization leakage. We present an overview of the SPTpol instrument design, project status, and science projections.
  10/2012;
• Article: Performance and on-sky optical characterization of the SPTpol instrument

  E. M. George, P. Ade, K. A. Aird, J. E. Austermann, J. A. Beall, D. Becker, A. Bender, B. A. Benson, L. E. Bleem, J. Britton, [......], E. Shirokoff, K. Story, C. Tucker, K. Vanderlinde, J. D. Vieira, G. Wang, R. Williamson, V. Yefremenko, K. W. Yoon, E. Young
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  ABSTRACT: In January 2012, the 10m South Pole Telescope (SPT) was equipped with a polarization-sensitive camera, SPTpol, in order to measure the polarization anisotropy of the cosmic microwave background (CMB). Measurements of the polarization of the CMB at small angular scales (~several arcminutes) can detect the gravitational lensing of the CMB by large scale structure and constrain the sum of the neutrino masses. At large angular scales (~few degrees) CMB measurements can constrain the energy scale of Inflation. SPTpol is a two-color mm-wave camera that consists of 180 polarimeters at 90 GHz and 588 polarimeters at 150 GHz, with each polarimeter consisting of a dual transition edge sensor (TES) bolometers. The full complement of 150 GHz detectors consists of 7 arrays of 84 ortho-mode transducers (OMTs) that are stripline coupled to two TES detectors per OMT, developed by the TRUCE collaboration and fabricated at NIST. Each 90 GHz pixel consists of two antenna-coupled absorbers coupled to two TES detectors, developed with Argonne National Labs. The 1536 total detectors are read out with digital frequency-domain multiplexing (DfMUX). The SPTpol deployment represents the first on-sky tests of both of these detector technologies, and is one of the first deployed instruments using DfMUX readout technology. We present the details of the design, commissioning, deployment, on-sky optical characterization and detector performance of the complete SPTpol focal plane.
  10/2012;
• Article: High-Redshift Cool-Core Galaxy Clusters Detected via the Sunyaev--Zel'dovich Effect in the South Pole Telescope Survey

  D. R. Semler, R. Šuhada, K. A. Aird, M. L. N. Ashby, M. Bautz, M. Bayliss, G. Bazin, S. Bocquet, B. A. Benson, L. E. Bleem, [......], A. A. Stark, K. Story, C. W. Stubbs, A. van Engelen, K. Vanderlinde, J. D. Vieira, A. Vikhlinin, R. Williamson, O. Zahn, A. Zenteno
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  ABSTRACT: We report the first investigation of cool-core properties of galaxy clusters selected via their Sunyaev--Zel'dovich (SZ) effect. We use 13 galaxy clusters uniformly selected from 178 deg^2 observed with the South Pole Telescope (SPT) and followed up by the Chandra X-ray Observatory. They form an approximately mass-limited sample (> 3 x 10^14 M_sun h^-1_70) spanning redshifts 0.3 < z < 1.1. Using previously published X-ray-selected cluster samples, we compare two proxies of cool-core strength: surface brightness concentration (cSB) and cuspiness ({\alpha}). We find that cSB is better constrained. We measure cSB for the SPT sample and find several new z > 0.5 cool-core clusters, including two strong cool cores. This rules out the hypothesis that there are no z > 0.5 clusters that qualify as strong cool cores at the 5.4{\sigma} level. The fraction of strong cool-core clusters in the SPT sample in this redshift regime is between 7% and 56% (95% confidence). Although the SPT selection function is significantly different from the X-ray samples, the high-z cSB distribution for the SPT sample is statistically consistent with that of X-ray-selected samples at both low and high redshifts. The cool-core strength is inversely correlated with the offset between the brightest cluster galaxy and the X-ray centroid, providing evidence that the dynamical state affects the cool-core strength of the cluster. Larger SZ-selected samples will be crucial in understanding the evolution of cluster cool cores over cosmic time.
  08/2012;
• Article: A massive, cooling-flow-induced starburst in the core of a luminous cluster of galaxies.

  M McDonald, M Bayliss, B A Benson, R J Foley, J Ruel, P Sullivan, S Veilleux, K A Aird, M L N Ashby, M Bautz, [......], K Story, C W Stubbs, R Suhada, A van Engelen, K Vanderlinde, J D Vieira, A Vikhlinin, R Williamson, O Zahn, A Zenteno
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  ABSTRACT: In the cores of some clusters of galaxies the hot intracluster plasma is dense enough that it should cool radiatively in the cluster's lifetime, leading to continuous 'cooling flows' of gas sinking towards the cluster centre, yet no such cooling flow has been observed. The low observed star-formation rates and cool gas masses for these 'cool-core' clusters suggest that much of the cooling must be offset by feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical and infrared observations of the galaxy cluster SPT-CLJ2344-4243 (ref. 11) at redshift z = 0.596. These observations reveal an exceptionally luminous (8.2 × 10(45) erg s(-1)) galaxy cluster that hosts an extremely strong cooling flow (around 3,820 solar masses a year). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (formation of around 740 solar masses a year), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool-core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star-formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form through accretion of the intracluster medium, rather than (as is currently thought) assembling entirely via mergers.
  Nature 08/2012; 488(7411):349-52. · 36.28 Impact Factor
• Article: A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly Luminous Galaxy Cluster

  M. McDonald, M. Bayliss, B. A. Benson, R. J. Foley, J. Ruel, P. Sullivan, S. Veilleux, K. A. Aird, M. L. N. Ashby, M. Bautz, [......], K. Story, C. W. Stubbs, R. Suhada, A. van Engelen, K. Vanderlinde, J. D. Vieira, A. Vikhlinin, R. Williamson, O. Zahn, A. Zenteno
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  ABSTRACT: In the cores of some galaxy clusters the hot intracluster plasma is dense enough that it should cool radiatively in the cluster's lifetime, leading to continuous "cooling flows" of gas sinking towards the cluster center, yet no such cooling flow has been observed. The low observed star formation rates and cool gas masses for these "cool core" clusters suggest that much of the cooling must be offset by astrophysical feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical, and infrared observations of the galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an exceptionally luminous (L_2-10 keV = 8.2 x 10^45 erg/s) galaxy cluster which hosts an extremely strong cooling flow (dM/dt = 3820 +/- 530 Msun/yr). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (740 +/- 160 Msun/yr), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form via accretion of the intracluster medium, rather than the current picture of central galaxies assembling entirely via mergers.
  08/2012;
• Article: Redshifts, Sample Purity, and BCG Positions for the Galaxy Cluster Catalog from the first 720 Square Degrees of the South Pole Telescope Survey

  J. Song, A. Zenteno, B. Stalder, S. Desai, L. E. Bleem, K. A. Aird, R. Armstrong, M. L. N. Ashby, M. Bayliss, G. Bazin, [......], S. A. Stanford, Z. Staniszewski, A. A. Stark, K. Story, C. W. Stubbs, A. van Engelen, K. Vanderlinde, J. D. Vieira, R. Williamson, O. Zahn
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  ABSTRACT: We present the results of the ground- and space-based optical and near-infrared (NIR) follow-up of 224 galaxy cluster candidates detected with the Sunyaev-Zel'dovich (SZ) effect in the 720 deg^2 of the South Pole Telescope (SPT) survey completed in the 2008 and 2009 observing seasons. We use the optical/NIR data to establish whether each candidate is associated with an overdensity of galaxies and to estimate the cluster redshift. Most photometric redshifts are derived through a combination of three different cluster redshift estimators using red-sequence galaxies, resulting in an accuracy of \Delta z/(1+z)=0.017, determined through comparison with a subsample of 57 clusters for which we have spectroscopic redshifts. We successfully measure redshifts for 158 systems and present redshift lower limits for the remaining candidates. The redshift distribution of the confirmed clusters extends to z=1.35 with a median of z_{med}=0.57. Approximately 18% of the sample with measured redshifts lies at z>0.8. We estimate a lower limit to the purity of this SPT SZ-selected sample by assuming that all unconfirmed clusters are noise fluctuations in the SPT data. We show that the cumulative purity at detection significance \xi>5 (\xi>4.5) is >= 95 (>= 70%). We present the red brightest cluster galaxy (rBCG) positions for the sample and examine the offsets between the SPT candidate position and the rBCG. The radial distribution of offsets is similar to that seen in X-ray-selected cluster samples, providing no evidence that SZ-selected cluster samples include a different fraction of recent mergers than X-ray-selected cluster samples.
  07/2012;
• Article: Frequency multiplexed superconducting quantum interference device readout of large bolometer arrays for cosmic microwave background measurements.

  M A Dobbs, M Lueker, K A Aird, A N Bender, B A Benson, L E Bleem, J E Carlstrom, C L Chang, H-M Cho, J Clarke, [......], D Schwan, E Shirokoff, H G Spieler, Z Staniszewski, A A Stark, K Vanderlinde, J D Vieira, C Vu, B Westbrook, R Williamson
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  ABSTRACT: A technological milestone for experiments employing transition edge sensor bolometers operating at sub-Kelvin temperature is the deployment of detector arrays with 100s-1000s of bolometers. One key technology for such arrays is readout multiplexing: the ability to read out many sensors simultaneously on the same set of wires. This paper describes a frequency-domain multiplexed readout system which has been developed for and deployed on the APEX-SZ and South Pole Telescope millimeter wavelength receivers. In this system, the detector array is divided into modules of seven detectors, and each bolometer within the module is biased with a unique ∼MHz sinusoidal carrier such that the individual bolometer signals are well separated in frequency space. The currents from all bolometers in a module are summed together and pre-amplified with superconducting quantum interference devices operating at 4 K. Room temperature electronics demodulate the carriers to recover the bolometer signals, which are digitized separately and stored to disk. This readout system contributes little noise relative to the detectors themselves, is remarkably insensitive to unwanted microphonic excitations, and provides a technology pathway to multiplexing larger numbers of sensors.
  The Review of scientific instruments 07/2012; 83(7):073113. · 1.52 Impact Factor
• Article: Submillimeter Observations of Millimeter Bright Galaxies Discovered by the South Pole Telescope

  T. R. Greve, J. D. Vieira, A. Weiss, J. E. Aguirre, K. A. Aird, M. L. N. Ashby, B. A. Benson, L. E. Bleem, C. M. Bradford, M. Brodwin, [......], E. Shirokoff, B. Stalder, S. A. Stanford, Z. Staniszewski, A. A. Stark, K. Story, K. Vanderlinde, W. Walsh, N. Welikala, R. Williamson
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  ABSTRACT: We present APEX SABOCA 350micron and LABOCA 870micron observations of 11 representative examples of the rare, extremely bright (S_1.4mm > 15mJy), dust-dominated millimeter-selected galaxies recently discovered by the South Pole Telescope (SPT). All 11 sources are robustly detected with LABOCA with 40 < S_870micron < 130mJy, approximately an order of magnitude higher than the canonical submillimeter galaxy (SMG) population. Six of the sources are also detected by SABOCA at >3sigma, with the detections or upper limits providing a key constraint on the shape of the spectral energy distribution (SED) near its peak. We model the SEDs of these galaxies using a simple modified blackbody and perform the same analysis on samples of SMGs of known redshift from the literature. These calibration samples inform the distribution of dust temperature for similar SMG populations, and this dust temperature prior allows us to derive photometric redshift estimates and far infrared luminosities for the sources. We find a median redshift of = 3.0, higher than the = 2.2 inferred for the normal SMG population. We also derive the apparent size of the sources from the temperature and apparent luminosity, finding them to appear larger than our unlensed calibration sample, which supports the idea that these sources are gravitationally magnified by massive structures along the line of sight.
  06/2012;
• Article: SPT-CL J0205-5829: A z = 1.32 Evolved Massive Galaxy Cluster in the South Pole Telescope Sunyaev-Zel'dovich Effect Survey

  B. Stalder, J. Ruel, R. Suhada, M. Brodwin, K. A. Aird, K. Andersson, R. Armstrong, M. L. N. Ashby, M. Bautz, M. Bayliss, [......], A. A. Stark, K. Story, C. W. Stubbs, A. van Engelen, K. Vanderlinde, J. D. Vieira, A. Vikhlinin, R. Williamson, O. Zahn, A. Zenteno
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  ABSTRACT: The galaxy cluster SPT-CL J0205-5829 currently has the highest spectroscopically-confirmed redshift, z=1.322, in the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. XMM-Newton observations measure a core-excluded temperature of Tx=8.7keV producing a mass estimate that is consistent with the Sunyaev-Zel'dovich derived mass. The combined SZ and X-ray mass estimate of M500=(4.9+/-0.8)e14 h_{70}^{-1} Msun makes it the most massive known SZ-selected galaxy cluster at z>1.2 and the second most massive at z>1. Using optical and infrared observations, we find that the brightest galaxies in SPT-CL J0205-5829 are already well evolved by the time the universe was <5 Gyr old, with stellar population ages >3 Gyr, and low rates of star formation (<0.5Msun/yr). We find that, despite the high redshift and mass, the existence of SPT-CL J0205-5829 is not surprising given a flat LambdaCDM cosmology with Gaussian initial perturbations. The a priori chance of finding a cluster of similar rarity (or rarer) in a survey the size of the 2500 deg^2 SPT-SZ survey is 69%.
  05/2012;
• Article: Weak-Lensing Mass Measurements of Five Galaxy Clusters in the South Pole Telescope Survey Using Magellan/Megacam

  F. W. High, H. Hoekstra, N. Leethochawalit, T. de Haan, L. Abramson, K. A. Aird, R. Armstrong, M. L. N. Ashby, M. Bautz, M. Bayliss, [......], C. W. Stubbs, R. Suhada, S. Tokarz, A. van Engelen, K. Vanderlinde, J. D. Vieira, A. Vikhlinin, R. Williamson, O. Zahn, A. Zenteno
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  ABSTRACT: We use weak gravitational lensing to measure the masses of five galaxy clusters selected from the South Pole Telescope (SPT) survey, with the primary goal of comparing these with the SPT Sunyaev--Zel'dovich (SZ) and X-ray based mass estimates. The clusters span redshifts 0.28 < z < 0.43 and have masses M_500 > 2 x 10^14 h^-1 M_sun, and three of the five clusters were discovered by the SPT survey. We observed the clusters in the g'r'i' passbands with the Megacam imager on the Magellan Clay 6.5m telescope. We measure a mean ratio of weak lensing (WL) aperture masses to inferred aperture masses from the SZ data, both within an aperture of R_500,SZ derived from the SZ mass, of 1.04 +/- 0.18. We measure a mean ratio of spherical WL masses evaluated at R_500,SZ to spherical SZ masses of 1.07 +/- 0.18, and a mean ratio of spherical WL masses evaluated at R_500,WL to spherical SZ masses of 1.10 +/- 0.24. We explore potential sources of systematic error in the mass comparisons and conclude that all are subdominant to the statistical uncertainty, with dominant terms being cluster concentration uncertainty and N-body simulation calibration bias. Expanding the sample of SPT clusters with WL observations has the potential to significantly improve the SPT cluster mass calibration and the resulting cosmological constraints from the SPT cluster survey. These are the first WL detections using Megacam on the Magellan Clay telescope.
  05/2012;