Joanna Dunkley

Publications (36)44.86 Total impact

• Article: Cosmological Parameters from Pre-Planck CMB Measurements

  Erminia Calabrese, Renée A. Hlozek, Nick Battaglia, Elia S. Battistelli, J. Richard Bond, Jens Chluba, Devin Crichton, Sudeep Das, Mark J. Devlin, Joanna Dunkley, [......], Michael R. Nolta, Lyman A. Page, Neelima Sehgal, Blake D. Sherwin, Jonathan L. Sievers, Cristóbal Sifón, David N. Spergel, Suzanne T. Staggs, Eric R. Switzer, Edward J. Wollack
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  ABSTRACT: Recent data from the WMAP, ACT and SPT experiments provide precise measurements of the cosmic microwave background temperature power spectrum over a wide range of angular scales. The combination of these observations is well fit by the standard, spatially flat LCDM cosmological model, constraining six free parameters to within a few percent. The scalar spectral index, n_s = 0.9690 +/- 0.0089, is less than unity at the 3.6 sigma level, consistent with simple models of inflation. The damping tail of the power spectrum at high resolution, combined with the amplitude of gravitational lensing measured by ACT and SPT, constrains the effective number of relativistic species to be N_eff = 3.28 +/- 0.40, in agreement with the standard model's three species of light neutrinos.
  02/2013;
• Article: The Atacama Cosmology Telescope: Temperature and Gravitational Lensing Power Spectrum Measurements from Three Seasons of Data

  Sudeep Das, Thibaut Louis, Michael R. Nolta, Graeme E. Addison, Elia S. Battistelli, J Richard Bond, Erminia Calabrese, Devin Crichton Mark J. Devlin, Simon Dicker, Joanna Dunkley, [......], Neelima Sehgal, Blake D. Sherwin, Jonathan L. Sievers, David N. Spergel, Suzanne T. Staggs, Daniel S. Swetz, Eric R. Switzer, Robert Thornton, Hy Trac, Ed Wollack
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  ABSTRACT: We present the temperature power spectra of the cosmic microwave background (CMB) derived from the three seasons of data from the Atacama Cosmology Telescope (ACT) at 148 GHz and 218 GHz, as well as the cross-frequency spectrum between the two channels. We detect and correct for contamination due to the Galactic cirrus in our equatorial maps. We present the results of a number of tests for possible systematic error and conclude that any effects are not significant compared to the statistical errors we quote. Where they overlap, we cross-correlate the ACT and the South Pole Telescope (SPT) maps and show they are consistent. The measurements of higher-order peaks in the CMB power spectrum provide an additional test of the Lambda CDM cosmological model, and help constrain extensions beyond the standard model. The small angular scale power spectrum also provides constraining power on the Sunyaev-Zel'dovich effects and extragalactic foregrounds. We also present a measurement of the CMB gravitational lensing convergence power spectrum at 4.6-sigma detection significance.
  01/2013;
• Article: The Atacama Cosmology Telescope: Cosmological parameters from three seasons of data

  Jonathan L. Sievers, Renée A. Hlozek, Michael R. Nolta, Viviana Acquaviva, Graeme E. Addison, Peter A. R. Ade, Paula Aguirre, Mandana Amiri, John William Appel, L. Felipe Barrientos, [......], Robert Thornton, Hy Trac, Carole Tucker, Masao Uehara, Katerina Visnjic, Ryan Warne, Grant Wilson, Ed Wollack, Yue Zhao, Caroline Zuncke
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  ABSTRACT: We present constraints on cosmological and astrophysical parameters from high-resolution microwave background maps at 148 GHz and 218 GHz made by the Atacama Cosmology Telescope (ACT) in three seasons of observations from 2008 to 2010. A model of primary cosmological and secondary foreground parameters is fit to the map power spectra and lensing deflection power spectrum, including contributions from both the thermal Sunyaev-Zeldovich (tSZ) effect and the kinematic Sunyaev-Zeldovich (kSZ) effect, Poisson and correlated anisotropy from unresolved infrared sources, radio sources, and the correlation between the tSZ effect and infrared sources. The power ell^2 C_ell/2pi of the thermal SZ power spectrum at 148 GHz is measured to be 3.4 +/-1.4 muK^2 at ell=3000, while the corresponding amplitude of the kinematic SZ power spectrum has a 95 percent confidence level upper limit of 8.6 muK^2. Combining ACT power spectra with the WMAP 7-year temperature and polarization power spectra, we find excellent consistency with the LCDM model. We constrain the number of effective relativistic degrees of freedom in the early universe to be Neff=2.79 +/-0.56, in agreement with the canonical value of Neff=3.046 for three massless neutrinos. We constrain the sum of the neutrino masses to be Sigma m_nu < 0.39 eV at 95% confidence when combining ACT and WMAP 7-year data with BAO and Hubble constant measurements. We constrain the amount of primordial helium to be Yp = 0.225 +/-0.034, and measure no variation in the fine structure constant alpha since recombination, with alpha/alpha_0 = 1.004+/- 0.005. We also find no evidence for any running of the scalar spectral index, dns/dln k = -0.004 +/- 0.012.
  01/2013;
• Article: The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz from Three Seasons of Data

  Matthew Hasselfield, Matt Hilton, Tobias A. Marriage, Graeme E. Addison, L. Felipe Barrientos, Nick Battaglia, Elia S. Battistelli, J. Richard Bond, Devin Crichton, Sudeep Das, [......], Blake D. Sherwin, Jon Sievers, Cristóbal Sifón, David N. Spergel, Suzanne T. Staggs, Daniel S. Swetz, Eric R. Switzer, Robert Thornton, Hy Trac, Edward J. Wollack
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  ABSTRACT: [Abridged] We present a catalog of 68 galaxy clusters, of which 19 are new discoveries, detected via the Sunyaev-Zel'dovich effect (SZ) at 148 GHz in the Atacama Cosmology Telescope (ACT) survey of 504 square degrees on the celestial equator. A subsample of 48 clusters within the 270 square degree region overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14 Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters, the sample is studied further through a "Profile Based Amplitude Analysis" using a single filter at a fixed \theta_500 = 5.9' angular scale. This new approach takes advantage of the "Universal Pressure Profile" (UPP) to break the degeneracy between the cluster extent (R_500) and the integrated Compton parameter (Y_500). The UPP scalings are found to be nearly identical to an adiabatic model, while a model incorporating non-thermal pressure better matches dynamical mass measurements and masses from the South Pole Telescope. A complete, high signal to noise ratio subsample of 15 ACT clusters is used to obtain cosmological constraints. We first confirm that constraints from SZ data are limited by uncertainty in the scaling relation parameters rather than sample size or measurement uncertainty. We next add in seven clusters from the ACT Southern survey, including their dynamical mass measurements based on galaxy velocity dispersions. In combination with WMAP7 these data simultaneously constrain the scaling relation and cosmological parameters, yielding \sigma_8 = 0.829 \pm 0.024 and \Omega_m = 0.292 \pm 0.025. The results include marginalization over a 15% bias in dynamical mass relative to the true halo mass. In an extension to LCDM that incorporates non-zero neutrino mass density, we combine our data with WMAP7+BAO+Hubble constant measurements to constrain \Sigma m_\nu < 0.29 eV (95% C. L.).
  01/2013;
• Article: Constraining thermal dust emission in distant galaxies with number counts and angular power spectra

  Graeme E. Addison, Joanna Dunkley, J. Richard Bond
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  ABSTRACT: We perform a joint fit to differential number counts from Spitzer's MIPS and Herschel's SPIRE instruments, and angular power spectra of cosmic infrared background (CIB) anisotropies from SPIRE, Planck, the Atacama Cosmology Telescope, and the South Pole Telescope, which together span 220 < \nu / GHz < 4300 (70 < \lambda / \mu m < 1400). We simultaneously constrain the dust luminosity function, thermal dust spectral energy distribution (SED) and clustering properties of CIB sources, and the evolution of these quantities over cosmic time. We find that the data strongly require redshift evolution in the thermal dust SED. In our adopted parametrization, this evolution takes the form of an increase in graybody dust temperature at high redshift, but it may also be related to a temperature - dust luminosity correlation or evolution in dust opacity. The counts and spectra together constrain the evolution of the thermal dust luminosity function up to z ~ 2.5-3, complementing approaches relying on rest-frame mid-infrared observations of the rarest bright objects. We are able to fit the power spectra without requiring a complex halo model approach, and show that neglecting scale-dependent halo bias may be impairing analyses that do use this framework. Our model has considerable predictive power and can be used to calculate any one- or two-point statistic of the CIB over a wide range of frequency and angular scale.
  10/2012;
• Article: The Atacama Cosmology Telescope: Data Characterization and Map Making

  Rolando Dünner, Matthew Hasselfield, Tobias A. Marriage, Jon Sievers, Viviana Acquaviva, Graeme E. Addison, Peter A. R. Ade, Paula Aguirre, Mandana Amiri, John William Appel, [......], Suzanne T. Staggs, Daniel S. Swetz, Eric R. Switzer, Robert Thornton, Hy Trac, Carole Tucker, Ryan Warne, Grant Wilson, Ed Wollack, Yue Zhao
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  ABSTRACT: We present a description of the data reduction and mapmaking pipeline used for the 2008 observing season of the Atacama Cosmology Telescope (ACT). The data presented here at 148 GHz represent 12% of the 90 TB collected by ACT from 2007 to 2010. In 2008 we observed for 136 days, producing a total of 1423 hours of data (11 TB for the 148 GHz band only), with a daily average of 10.5 hours of observation. From these, 1085 hours were devoted to a 850 deg^2 stripe (11.2 hours by 9.1 deg) centered on a declination of -52.7 deg, while 175 hours were devoted to a 280 deg^2 stripe (4.5 hours by 4.8 deg) centered at the celestial equator. We discuss sources of statistical and systematic noise, calibration, telescope pointing, and data selection. Out of 1260 survey hours and 1024 detectors per array, 816 hours and 593 effective detectors remain after data selection for this frequency band, yielding a 38% survey efficiency. The total sensitivity in 2008, determined from the noise level between 5 Hz and 20 Hz in the time-ordered data stream (TOD), is 32 micro-Kelvin sqrt{s} in CMB units. Atmospheric brightness fluctuations constitute the main contaminant in the data and dominate the detector noise covariance at low frequencies in the TOD. The maps were made by solving the least-squares problem using the Preconditioned Conjugate Gradient method, incorporating the details of the detector and noise correlations. Cross-correlation with WMAP sky maps, as well as analysis from simulations, reveal that our maps are unbiased at multipoles ell > 300. This paper accompanies the public release of the 148 GHz southern stripe maps from 2008. The techniques described here will be applied to future maps and data releases.
  07/2012;
• Article: The Atacama Cosmology Telescope: Cross-Correlation of CMB Lensing and Quasars

  Blake D. Sherwin, Sudeep Das, Amir Hajian, Graeme Addison, J. Richard Bond, Devin Crichton, Mark J. Devlin, Joanna Dunkley, Megan B. Gralla, Mark Halpern, [......], Michael D. Niemack, Lyman A. Page, Erik D. Reese, Neelima Sehgal, Jon Sievers, Cristobal Sifon, David N. Spergel, Suzanne T. Staggs, Eric R. Switzer, Ed Wollack
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  ABSTRACT: We measure the cross-correlation of Atacama Cosmology Telescope CMB lensing convergence maps with quasar maps made from the Sloan Digital Sky Survey DR8 SDSS-XDQSO photometric catalog. The CMB lensing-quasar cross-power spectrum is detected for the first time at a significance of 3.8 sigma, which directly confirms that the quasar distribution traces the mass distribution at high redshifts z>1. Our detection passes a number of null tests and systematic checks. Using this cross-power spectrum, we measure the amplitude of the linear quasar bias assuming a template for its redshift dependence, and find the amplitude to be consistent with an earlier measurement from clustering; at redshift z ~ 1.4, the peak of the distribution of quasars in our maps, our measurement corresponds to a bias of b = 2.5 +/- 0.6. With the signal-to-noise ratio on CMB lensing measurements likely to improve by an order of magnitude over the next few years, our results demonstrate the potential of CMB lensing cross-correlations to probe astrophysics at high redshifts.
  07/2012;
• Article: The Atacama Cosmology Telescope: Relation Between Galaxy Cluster Optical Richness and Sunyaev-Zel'dovich Effect

  Neelima Sehgal, Graeme Addison, Nick Battaglia, Elia S. Battistelli, J. Richard Bond, Sudeep Das, Mark J. Devlin, Joanna Dunkley, Rolando Dünner, Megan Gralla, [......], Bruce Partridge, Erik D. Reese, Blake D. Sherwin, Jon Sievers, Cristóbal Sifón, David N. Spergel, Suzanne T. Staggs, Daniel S. Swetz, Eric R. Switzer, Ed Wollack
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  ABSTRACT: We present the measured Sunyaev-Zel'dovich (SZ) flux from 474 optically-selected MaxBCG clusters that fall within the Atacama Cosmology Telescope (ACT) Equatorial survey region. The ACT Equatorial region used in this analysis covers 510 square degrees and overlaps Stripe 82 of the Sloan Digital Sky Survey. We also present the measured SZ flux stacked on 52 X-ray-selected MCXC clusters that fall within the ACT Equatorial region and an ACT Southern survey region covering 455 square degrees. We find that the measured SZ flux from the X-ray-selected clusters is consistent with expectations. However, we find that the measured SZ flux from the optically-selected clusters is both significantly lower than expectations and lower than the recovered SZ flux measured by the Planck satellite. Since we find a lower recovered SZ signal than Planck, we investigate the possibility that there is a significant offset between the optically-selected brightest cluster galaxies (BCGs) and the SZ centers, to which ACT is more sensitive due to its finer resolution. Such offsets can arise due to either an intrinsic physical separation between the BCG and the center of the gas concentration or from misidentification of the cluster BCG. We find that the entire discrepancy for both ACT and Planck can be explained by assuming that the BCGs are offset from the SZ maxima with a uniform random distribution between 0 and 1.5 Mpc. Such large offsets between gas peaks and BCGs for optically-selected cluster samples seem unlikely given that we find the physical separation between BCGs and X-ray peaks for an X-ray-selected subsample of MaxBCG clusters to have a much narrower distribution that peaks within 0.2 Mpc. It is possible that other effects are lowering the ACT and Planck signals by the same amount, with offsets between BCGs and SZ peaks explaining the remaining difference between measurements. (Abridged)
  05/2012;
• Article: Modelling the correlation between the thermal Sunyaev Zel'dovich effect and the cosmic infrared background

  Graeme E. Addison, Joanna Dunkley, David N. Spergel
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  ABSTRACT: We show how the correlation between the thermal Sunyaev Zel'dovich effect (tSZ) from galaxy clusters and dust emission from cosmic infrared background (CIB) sources can be calculated in a halo model framework. Using recent tSZ and CIB models, we find that the size of the tSZ x CIB cross-correlation is approximately 20 per cent at 150 GHz. The contribution to the total angular power spectrum is of order -2 \mu K^2 at ell=3000, however, this value is uncertain by a factor of two to three, primarily because of CIB source modelling uncertainties. We expect the large uncertainty in this component to degrade upper limits on the kinematic Sunyaev Zel'dovich effect (kSZ), due to similarity in the frequency dependence of the tSZ x CIB and kSZ across the frequency range probed by current Cosmic Microwave Background missions. We also find that the degree of tSZ x CIB correlation is higher for mm x sub-mm spectra than mm x mm, because more of the sub-mm CIB originates at lower redshifts (z<2), where most tSZ clusters are found.
  04/2012;
• Article: The Atacama Cosmology Telescope: A Measurement of the Thermal Sunyaev-Zel'dovich Effect Using the Skewness of the CMB Temperature Distribution

  Michael J. Wilson, Blake D. Sherwin, J. Colin Hill, Graeme Addison, Nick Battaglia, J. Richard Bond, Sudeep Das, Mark J. Devlin, Joanna Dunkley, Rolando Dunner, [......], Bruce Partridge, Erik D. Reese, Neelima Sehgal, Jon Sievers, David N. Spergel, Suzanne T. Staggs, Daniel S. Swetz, Eric R. Switzer, Hy Trac, Ed Wollack
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  ABSTRACT: We present a detection of the unnormalized skewness <T^3> induced by the thermal Sunyaev-Zel'dovich (tSZ) effect in filtered Atacama Cosmology Telescope (ACT) 148 GHz cosmic microwave background temperature maps. Contamination due to infrared and radio sources is minimized by template subtraction of resolved sources and by constructing a mask using outlying values in the 218 GHz (tSZ-null) ACT maps. We measure <T^3>= -31 +- 6 \mu K^3 (measurement error only) or +- 14 \mu K^3 (including cosmic variance error) in the filtered ACT data, a 5-sigma detection. We show that the skewness is a sensitive probe of sigma_8, and use analytic calculations and tSZ simulations to obtain cosmological constraints from this measurement. From this signal alone we infer a value of sigma_8= 0.79 +0.03 -0.03 (68 % C.L.) +0.06 -0.06 (95 % C.L.). Our results demonstrate that measurements of non-Gaussianity can be a useful method for characterizing the tSZ effect and extracting the underlying cosmological information.
  03/2012;
• Article: Evidence of Galaxy Cluster Motions with the Kinematic Sunyaev-Zel'dovich Effect

  Nick Hand, Graeme E. Addison, Eric Aubourg, Nick Battaglia, Elia S. Battistelli, Dmitry Bizyaev, J. Richard Bond, Howard Brewington, Jon Brinkmann, Benjamin R. Brown, [......], Stephanie Snedden, David N. Spergel, Suzanne T. Staggs, Daniel S. Swetz, Eric R. Switzer, Hy Trac, Benjamin A. Weaver, Edward J. Wollack, Christophe Yeche, Caroline Zunckel
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  ABSTRACT: Using high-resolution microwave sky maps made by the Atacama Cosmology Telescope, we for the first time present strong evidence for motions of galaxy clusters and groups via microwave background temperature distortions due to the kinematic Sunyaev-Zel'dovich effect. Galaxy clusters are identified by their constituent luminous galaxies observed by the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. We measure the mean pairwise momentum of clusters, with a probability of the signal being due to random errors of 0.002, and the signal is consistent with the growth of cosmic structure in the standard model of cosmology.
  03/2012;
• Source

  Available from: Clive Dickinson

  Article: Impact on the tensor-to-scalar ratio of incorrect Galactic foreground modelling

  Charmaine Armitage-Caplan, Joanna Dunkley, Hans Kristian Eriksen, Clive Dickinson
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  ABSTRACT: A key goal of many Cosmic Microwave Background experiments is the detection of gravitational waves, through their B-mode polarization signal at large scales. To extract such a signal requires modelling contamination from the Galaxy. Using the Planck experiment as an example, we investigate the impact of incorrectly modelling foregrounds on estimates of the polarized CMB, quantified by the bias in tensor-to-scalar ratio r, and optical depth tau. We use a Bayesian parameter estimation method to estimate the CMB, synchrotron, and thermal dust components from simulated observations spanning 30-353 GHz, starting from a model that fits the simulated data, returning r<0.03 at 95% confidence for an r=0 model, and r=0.09+-0.03 for an r=0.1 model. We then introduce a set of mismatches between the simulated data and assumed model. Including a curvature of the synchrotron spectral index with frequency, but assuming a power-law model, can bias r high by ~1-sigma (delta r ~ 0.03). A similar bias is seen for thermal dust with a modified black-body frequency dependence, incorrectly modelled as a power-law. If too much freedom is allowed in the model, for example fitting for spectral indices in 3 degree pixels over the sky with physically reasonable priors, we find r can be biased up to ~3-sigma high by effectively setting the indices to the wrong values. Increasing the signal-to-noise ratio by reducing parameters, or adding additional foreground data, reduces the bias. We also find that neglecting a 1% polarized free-free or spinning dust component has a negligible effect on r. These tests highlight the importance of modelling the foregrounds in a way that allows for sufficient complexity, while minimizing the number of free parameters.
  03/2012;
• Source

  Available from: Cristóbal Sifón

  Article: The Atacama Cosmology Telescope: Dynamical Masses and Scaling Relations for a Sample of Massive Sunyaev-Zel'dovich Effect Selected Galaxy Clusters

  Cristobal Sifon, Felipe Menanteau, Matthew Hasselfield, Tobias A. Marriage, John P. Hughes, L. Felipe Barrientos, Jorge Gonzalez, Leopoldo Infante, Graeme E. Addison, Andrew J. Baker, [......], Lyman A. Page, Bruce Partridge, Erik D. Reese, Neelima Sehgal, Jon Sievers, David N. Spergel, Suzanne T. Staggs, Robert J. Thornton, Hy Trac, Edward Wollack
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  ABSTRACT: We present the first dynamical mass estimates and scaling relations for a sample of Sunyaev-Zel'dovich effect (SZE) selected galaxy clusters. The sample consists of 16 massive clusters detected with the Atacama Cosmology Telescope (ACT) over a 455 sq. deg. area of the southern sky. Deep multi-object spectroscopic observations were taken to secure intermediate-resolution (R~700-800) spectra and redshifts for ~60 member galaxies on average per cluster. The dynamical masses M_200c of the clusters have been calculated using simulation-based scaling relations between velocity dispersion and mass. The sample has a median redshift z=0.50 and a median mass M_200c~12e14 Msun/h70 with a lower limit M_200c~6e14 Msun/h70, consistent with the expectations for the ACT southern sky survey. These masses are compared to the ACT SZE properties of the sample, specifically, the match-filtered central SZE amplitude y~, the central Compton parameter y0, and the integrated Compton signal Y_200c, which we use to derive SZE-Mass scaling relations. All SZE estimators correlate with dynamical mass with low intrinsic scatter (<~20%), in agreement with numerical simulations. We explore the effects of various systematic effects on these scaling relations, including the correlation between observables and the influence of dynamically disturbed clusters. Using the 3-dimensional information available, we divide the sample into relaxed and disturbed clusters and find that ~50% of the clusters are disturbed. There are hints that disturbed systems might bias the scaling relations but given the current sample sizes these differences are not significant; further studies including more clusters are required to assess the impact of these clusters on the scaling relations.
  01/2012;
• Article: Correlations in the (Sub)millimeter Background from ACT × BLAST

  Amir Hajian, Marco P. Viero, Graeme Addison, Paula Aguirre, John William Appel, Nick Battaglia, James J. Bock, J. Richard Bond, Sudeep Das, Mark J. Devlin, [......], Guillaume Patanchon, Douglas Scott, Neelima Sehgal, Jon Sievers, David N. Spergel, Suzanne T. Staggs, Daniel S. Swetz, Eric R. Switzer, Robert Thornton, and Ed Wollack
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  ABSTRACT: We present measurements of the auto- and cross-frequency correlation power spectra of the cosmic (sub)millimeter background at 250, 350, and 500 μm (1200, 860, and 600 GHz) from observations made with the Balloon-borne Large Aperture Submillimeter Telescope (BLAST); and at 1380 and 2030 μm (218 and 148 GHz) from observations made with the Atacama Cosmology Telescope (ACT). The overlapping observations cover 8.6 deg2 in an area relatively free of Galactic dust near the south ecliptic pole. The ACT bands are sensitive to radiation from the cosmic microwave background, to the Sunyaev-Zel'dovich effect from galaxy clusters, and to emission by radio and dusty star-forming galaxies (DSFGs), while the dominant contribution to the BLAST bands is from DSFGs. We confirm and extend the BLAST analysis of clustering with an independent pipeline and also detect correlations between the ACT and BLAST maps at over 25σ significance, which we interpret as a detection of the DSFGs in the ACT maps. In addition to a Poisson component in the cross-frequency power spectra, we detect a clustered signal at 4σ, and using a model for the DSFG evolution and number counts, we successfully fit all of our spectra with a linear clustering model and a bias that depends only on redshift and not on scale. Finally, the data are compared to, and generally agree with, phenomenological models for the DSFG population. This study demonstrates the constraining power of the cross-frequency correlation technique to constrain models for the DSFGs. Similar analyses with more data will impose tight constraints on future models.
  The Astrophysical Journal 12/2011; 744(1):40. · 6.02 Impact Factor
• Article: The Atacama Cosmology Telescope: Calibration with the Wilkinson Microwave Anisotropy Probe Using Cross-correlations

  Amir Hajian, Viviana Acquaviva, Peter A. R. Ade, Paula Aguirre, Mandana Amiri, John William Appel, L. Felipe Barrientos, Elia S. Battistelli, John R. Bond, Ben Brown, [......], David N. Spergel, Suzanne T. Staggs, Daniel S. Swetz, Eric R. Switzer, Robert Thornton, Hy Trac, Carole Tucker, Ryan Warne, Ed Wollack, and Yue Zhao
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  ABSTRACT: We present a new calibration method based on cross-correlations with the Wilkinson Microwave Anisotropy Probe (WMAP) and apply it to data from the Atacama Cosmology Telescope (ACT). ACT's observing strategy and map-making procedure allows an unbiased reconstruction of the modes in the maps over a wide range of multipoles. By directly matching the ACT maps to WMAP observations in the multipole range of 400 < l < 1000, we determine the absolute calibration with an uncertainty of 2% in temperature. The precise measurement of the calibration error directly impacts the uncertainties in the cosmological parameters estimated from the ACT power spectra. We also present a combined map based on ACT and WMAP data that has a high signal-to-noise ratio over a wide range of multipoles.
  The Astrophysical Journal 10/2011; 740(2):86. · 6.02 Impact Factor
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  Available from: ArXiv

  Article: Evidence for anomalous dust-correlated emission at 8 GHz

  Michelle Lu, Joanna Dunkley, Lyman Page
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  ABSTRACT: In 1969 Edward Conklin measured the anisotropy in celestial emission at 8 GHz with a resolution of 16.2 degrees and used the data to report a detection of the CMB dipole. Given the paucity of 8 GHz observations over large angular scales and the clear evidence for non-power law Galactic emission near 8 GHz, a new analysis of Conklin's data is informative. In this paper we compare Conklin's data to that from Haslam et al. (0.4 GHz), Reich and Reich (1.4 GHz), and WMAP (23-94 GHz). We show that the spectral index between Conklin's data and the 23 GHz WMAP data is beta=-1.7+-0.1, where we model the emission temperature as T \propto nu^beta. Free-free emission has beta \approx -2.15, synchrotron emission has beta \approx -2.7 to -3. Thermal dust emission (beta \approx1.7) is negligible at 8 GHz. We conclude that there must be another distinct non-power law component of diffuse foreground emission that emits near 10 GHz, consistent with other observations in this frequency range. By comparing to the full complement of data sets, we show that a model with an anomalous emission component, assumed to be spinning dust, is preferred over a model without spinning dust at 5 sigma (Delta chi2= 31). However, the source of the new component cannot be determined uniquely.
  09/2011;
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  Available from: Cristóbal Sifón

  Article: The Atacama Cosmology Telescope: ACT-CL J0102-4915 "El Gordo," a Massive Merging Cluster at Redshift 0.87

  Felipe Menanteau, John P. Hughes, Cristobal Sifon, Matt Hilton, Jorge Gonzalez, Leopoldo Infante, L. Felipe Barrientos, Andrew J. Baker, John R. Bond, Sudeep Das, [......], Kavilan Moodley, Michael D. Niemack, Michael R. Nolta, Lyman A. Page, Erik D. Reese, Neelima Sehgal, Jon Sievers, David N. Spergel, Suzanne T. Staggs, Edward Wollack
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  ABSTRACT: We present a detailed analysis from new multi-wavelength observations of the exceptional galaxy cluster ACT-CL J0102-4915 "El Gordo," likely the most massive, hottest, most X-ray luminous and brightest Sunyaev-Zeldovich (SZ) effect cluster known at z>0.6. The Atacama Cosmology Telescope collaboration discovered El Gordo as the most significant SZ decrement in a sky survey area of 755 deg^2. Our VLT/FORS2 spectra of 89 member galaxies yield a cluster redshift, z=0.870, and velocity dispersion, s=1321+/-106 km/s. Our Chandra observations reveal a hot and X-ray luminous system with an integrated temperature of Tx=14.5+/-1.0 keV and 0.5-2.0 keV band luminosity of Lx=(2.19+/-0.11)x10^45 h70^-2 erg/s. We obtain several statistically consistent cluster mass estimates; using mass scaling relations with velocity dispersion, X-ray Yx, and integrated SZ, we estimate a cluster mass of M200a=(2.16+/-0.32)x10^15 M_sun/h70. The Chandra and VLT/FORS2 optical data also reveal that El Gordo is undergoing a major merger between components with a mass ratio of approximately 2 to 1. The X-ray data show significant temperature variations from a low of 6.6+/-0.7 keV at the merging low-entropy, high-metallicity, cool core to a high of 22+/-6 keV. We also see a wake in the X-ray surface brightness caused by the passage of one cluster through the other. Archival radio data at 843 MHz reveal diffuse radio emission that, if associated with the cluster, indicates the presence of an intense double radio relic, hosted by the highest redshift cluster yet. El Gordo is possibly a high-redshift analog of the famous Bullet Cluster. Such a massive cluster at this redshift is rare, although consistent with the standard L-CDM cosmology in the lower part of its allowed mass range. Massive, high-redshift mergers like El Gordo are unlikely to be reproduced in the current generation of numerical N-body cosmological simulations.
  09/2011;
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  Available from: Edward J. Wollack

  Article: Power-Law Template for IR Point Source Clustering

  Graeme E. Addison, Joanna Dunkley, Amir Hajian, Marco Viero, J. Richard Bond, Sudeep Das, Mark Devlin, Mark Halpern, Adam Hincks, Renée Hlozek, Tobias A. Marriage, Kavilan Moodley, Lyman A. Page, Erik D. Reese, Douglas Scott, David N. Spergel, Suzanne T. Staggs, Edward Wollack
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  ABSTRACT: We perform a combined fit to angular power spectra of unresolved infrared (IR) point sources from the Planck satellite (at 217, 353, 545 and 857 GHz, over angular scales 100 < l < 2200), the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST; 250, 350 and 500 um; 1000 < l < 9000), and from correlating BLAST and Atacama Cosmology Telescope (ACT; 148 and 218 GHz) maps. We find that the clustered power over the range of angular scales and frequencies considered is well fit by a simple power law of the form C_l \propto l^-n with n = 1.25 +/- 0.06. While the IR sources are understood to lie at a range of redshifts, with a variety of dust properties, we find that the frequency dependence of the clustering power can be described by the square of a modified blackbody, nu^beta B(nu,T_eff), with a single emissivity index beta = 2.20 +/- 0.07 and effective temperature T_eff = 9.7 K. Our predictions for the clustering amplitude are consistent with existing ACT and South Pole Telescope results at around 150 and 220 GHz, as is our prediction for the effective dust spectral index, which we find to be alpha_150-220 = 3.68 +/- 0.07 between 150 and 220 GHz. Our constraints on the clustering shape and frequency dependence can be used to model the IR clustering as a contaminant in Cosmic Microwave Background anisotropy measurements. The combined Planck and BLAST data also rule out a linear bias clustering model.
  08/2011;
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  Available from: Katerina Visnjic

  Article: Evidence for dark energy from the cosmic microwave background alone using the Atacama Cosmology Telescope lensing measurements.

  Blake D Sherwin, Joanna Dunkley, Sudeep Das, John W Appel, J Richard Bond, C Sofia Carvalho, Mark J Devlin, Rolando Dünner, Thomas Essinger-Hileman, Joseph W Fowler, [......], Benjamin L Schmitt, Neelima Sehgal, Jon Sievers, David N Spergel, Suzanne T Staggs, Daniel S Swetz, Eric R Switzer, Robert Thornton, Katerina Visnjic, Ed Wollack
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  ABSTRACT: For the first time, measurements of the cosmic microwave background radiation (CMB) alone favor cosmologies with w = -1 dark energy over models without dark energy at a 3.2-sigma level. We demonstrate this by combining the CMB lensing deflection power spectrum from the Atacama Cosmology Telescope with temperature and polarization power spectra from the Wilkinson Microwave Anisotropy Probe. The lensing data break the geometric degeneracy of different cosmological models with similar CMB temperature power spectra. Our CMB-only measurement of the dark energy density Ω(Λ) confirms other measurements from supernovae, galaxy clusters, and baryon acoustic oscillations, and demonstrates the power of CMB lensing as a new cosmological tool.
  Physical Review Letters 07/2011; 107(2):021302. · 7.37 Impact Factor
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  Available from: Katerina Visnjic

  Article: Detection of the power spectrum of cosmic microwave background lensing by the Atacama Cosmology Telescope.

  Sudeep Das, Blake D Sherwin, Paula Aguirre, John W Appel, J Richard Bond, C Sofia Carvalho, Mark J Devlin, Joanna Dunkley, Rolando Dünner, Thomas Essinger-Hileman, [......], Benjamin L Schmitt, Neelima Sehgal, Jon Sievers, David N Spergel, Suzanne T Staggs, Daniel S Swetz, Eric R Switzer, Robert Thornton, Katerina Visnjic, Ed Wollack
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  ABSTRACT: We report the first detection of the gravitational lensing of the cosmic microwave background through a measurement of the four-point correlation function in the temperature maps made by the Atacama Cosmology Telescope. We verify our detection by calculating the levels of potential contaminants and performing a number of null tests. The resulting convergence power spectrum at 2° angular scales measures the amplitude of matter density fluctuations on comoving length scales of around 100 Mpc at redshifts around 0.5 to 3. The measured amplitude of the signal agrees with Lambda cold dark matter cosmology predictions. Since the amplitude of the convergence power spectrum scales as the square of the amplitude of the density fluctuations, the 4σ detection of the lensing signal measures the amplitude of density fluctuations to 12%.
  Physical Review Letters 07/2011; 107(2):021301. · 7.37 Impact Factor