Publications (140)619.83 Total impact
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ABSTRACT: We present galaxy velocity dispersions and dynamical mass estimates for 44 galaxy clusters selected via the SunyaevZel'dovich (SZ) effect by the Atacama Cosmology Telescope. Dynamical masses for 18 clusters are reported here for the first time. Using Nbody simulations, we model the different observing strategies used to measure the velocity dispersions and account for systematic effects resulting from these strategies. We find that the galaxy velocity distributions may be treated as isotropic, and that an aperture correction of up to 7 per cent in the velocity dispersion is required if the spectroscopic galaxy sample is sufficiently concentrated towards the cluster centre. Accounting for the radial profile of the velocity dispersion in simulations enables consistent dynamical mass estimates regardless of the observing strategy. Cluster masses $M_{200}$ are in the range $(115)\times10^{14}M_\odot$. Comparing with masses estimated from the SZ distortion assuming a gas pressure profile derived from Xray observations gives a mean SZtodynamical mass ratio of $1.10\pm0.13$, consistent with previous determinations at these mass scales.  [Show abstract] [Hide abstract]
ABSTRACT: We use microwave temperature maps from two seasons of data from the Atacama Cosmology Telescope (ACTPol) at 146 GHz, together with the Constant Mass CMASS galaxy sample from the Baryon Oscillation Spectroscopic Survey to measure the kinematic SunyaevZe\v{l}dovich (kSZ) effect over the redshift range z = 0.4  0.7. We use galaxy positions and the continuity equation to obtain a reconstruction of the lineofsight velocity field. We stack the cosmic microwave background temperature at the location of each halo, weighted by the corresponding reconstructed velocity. The resulting best fit kSZ model is preferred over the nokSZ hypothesis at 3.3sigma and 2.9sigma for two independent velocity reconstruction methods, using 25,537 galaxies over 660 square degrees. The effect of foregrounds that are uncorrelated with the galaxy velocities is expected to be well below our signal, and residual thermal SunyaevZe\v{l}dovich contamination is controlled by masking the most massive clusters. Finally, we discuss the systematics involved in converting our measurement of the kSZ amplitude into the mean free electron fraction of the halos in our sample.  [Show abstract] [Hide abstract]
ABSTRACT: Using a radioquiet subsample of the Sloan Digital Sky Survey spectroscopic quasar catalog, spanning redshifts 0.53.5, we derive the mean millimetre and farinfrared quasar spectral energy densities via a stacking analysis of Atacama Cosmology Telescope and HerschelSPIRE data. We constrain the form and evolution of the farinfrared emission finding 34$\sigma$ evidence for the presence of the thermal SunyaevZel'dovich (SZ) effect in the millimetre bands. We find this signal to be characteristic of a hot ionized gas component with thermal energy $(6.2 \pm 1.7) \times 10^{60}$erg. This amount of thermal energy is an order of magnitude greater than would be expected assuming only hot gas in virial equilibrium with the dark matter haloes of $(15)\times 10^{12}h^{1}$M$_\odot$ that these systems are expected to occupy, though the highest quasar mass estimates found in the literature could explain a large fraction of this energy. We find that our measurements are consistent with a scenario in which quasars deposit up to $(14.5 \pm 3.3)~\tau_8^{1}$ per cent of their radiative energy into their circumgalactic environment if their typical period of quasar activity is $\tau_8\times 10^8$ years. If quasar host masses are high ($\sim10^{13}h^{1}$M$_\odot$), then this percentage will be reduced significantly. Furthermore, the uncertainty quoted for this percentage is only statistical and additional systematic uncertainties (e.g., on quasar bolometric luminosity) enter at the 40 per cent level. Finally, emission from thermal dust is significant in these systems, with infrared luminosities of $\log_{10}(L_{\rm ir}/{\rm L}_\odot)=11.412.2$, increasing to higher redshift. We consider various models for dust emission. While sufficiently complex dust models can obviate the SZ effect, the SZ interpretation remains favoured at the 34$\sigma$ level for most models.  [Show abstract] [Hide abstract]
ABSTRACT: Mass calibration uncertainty is the largest systematic effect for using clusters of galaxies to constrain cosmological parameters. We present weak lensing mass measurements from the CanadaFranceHawaii Telescope Stripe 82 Survey for galaxy clusters selected through their high signaltonoise thermal SunyaevZeldovich (tSZ) signal measured with the Atacama Cosmology Telescope (ACT). The average weak lensing mass is $\left(4.8\pm0.8\right)\,\times10^{14}\,\mathrm{M}_\odot$, consistent with the tSZ mass estimate of $\left(4.70\pm1.0\right)\,\times10^{14}\,\mathrm{M}_\odot$ which assumes a universal pressure profile for the cluster gas. Our results are consistent with previous weaklensing measurements of tSZdetected clusters from the Planck satellite. When comparing our results, we estimate the Eddington bias correction for the sample intersection of Planck and weaklensing clusters which was previously neglected.  [Show abstract] [Hide abstract]
ABSTRACT: We present a measurement of the gravitational lensing of the Cosmic Microwave Background (CMB) temperature and polarization fields obtained by crosscorrelating the reconstructed convergence signal from the first season of ACTPol data at 146 GHz with Cosmic Infrared Background (CIB) fluctuations measured using the Planck satellite. Using an overlap area of 206 square degrees, we detect gravitational lensing of the CMB polarization by largescale structure at a statistical significance of 4.5 sigma. Combining both CMB temperature and polarization data gives a lensing detection at 9.1 sigma significance. A Bmode polarization lensing signal is present with a significance of 3.2 sigma. We also present the first measurement of CMB lensingCIB correlation at small scales corresponding to l > 2000. Null tests and systematic checks show that our results are not significantly biased by astrophysical or instrumental systematic effects, including Galactic dust. Fitting our measurements to the bestfit lensingCIB cross power spectrum measured in Planck data, scaled by an amplitude A, gives A=1.02 +0.12/0.18 (stat.) +/0.06(syst.), consistent with the Planck results.  [Show abstract] [Hide abstract]
ABSTRACT: Fullsky maps of the cosmic microwave background temperature reveal a 7% asymmetry of fluctuation power between two halves of the sky. A common phenomenological model for this asymmetry is an overall dipole modulation of statistically isotropic fluctuations, which produces particular offdiagonal correlations between multipole coefficients. We compute these correlations and construct corresponding estimators for the amplitude and direction of the dipole modulation. Applying these estimators to various cutsky temperature maps from Planck and WMAP data shows consistency with a dipole modulation, differing from a null signal at 2.5σ, with an amplitude and direction consistent with previous fits based on the temperature fluctuation power. The signal is scale dependent, with a statistically significant amplitude at angular scales larger than 2 degrees. Future measurements of microwave background polarization and gravitational lensing can increase the significance of the signal. If the signal is not a statistical fluke in an isotropic Universe, it requires new physics beyond the standard model of cosmology.  [Show abstract] [Hide abstract]
ABSTRACT: Twopoint correlation functions of cosmic microwave background polarization provide a physically independent probe of the surprising suppression of correlations in the cosmic microwave background temperature anisotropies at large angular scales. We investigate correlation functions constructed from both the Q and U Stokes parameters and from the E and B polarization components. The dominant contribution to these correlation functions comes from local physical effects at the last scattering surface or from the epoch of reionization at high redshift, so all should be suppressed if the temperature suppression is due to an underlying lack of correlations in the cosmological metric perturbations larger than a given scale. We evaluate the correlation functions for the standard $\Lambda$CDM cosmology constrained by the observed temperature correlation function, and compute statistics characterizing their suppression on large angular scales. Future fullsky polarization maps with minimal systematic errors on large angular scales will provide strong tests of whether the observed temperature correlation function is a statistical fluke or reflects a fundamental shortcoming of the standard cosmological model.  [Show abstract] [Hide abstract]
ABSTRACT: We present Southern African Large Telescope followup observations of seven massive clusters detected by the Atacama Cosmology Telescope (ACT) on the celestial equator using the Sunyaev–Zel'dovich (SZ) effect. We conducted multiobject spectroscopic observations with the Robert Stobie Spectrograph in order to measure galaxy redshifts in each cluster field, determine the cluster lineofsight velocity dispersions, and infer the cluster dynamical masses. We find that the clusters, which span the redshift range 0.3 < z < 0.55, range in mass from (5–20) × 1014 M⊙ (M200c). Their masses, given their SZ signals, are similar to those of Southern hemisphere ACT clusters previously observed using Gemini and the VLT. We note that the brightest cluster galaxy in one of the systems studied, ACTCL J0320.4+0032 at z = 0.38, hosts a type II quasar. Only a handful of such systems are currently known, and therefore ACTCL J0320.4+0032 may be a rare example of a very massive halo in which quasarmode feedback is actively taking place.  [Show abstract] [Hide abstract]
ABSTRACT: This paper was published online on 13 April 2015 with an error in an author’s name. The seventh author’s name should read as “Jerod Caligiuri.” The author’s name has been corrected as of 17 April 2015. The author’s name is correct in the printed version of the journal.  [Show abstract] [Hide abstract]
ABSTRACT: We present a statistical detection of the gravitational lensing of the cosmic microwave background by $10^{13}$ solar mass dark matter halos. Lensing convergence maps from the Atacama Cosmology Telescope Polarimeter (ACTPol) are stacked at the positions of around 12,000 opticallyselected CMASS galaxies from the SDSSIII/BOSS survey. The mean lensing signal is consistent with simulated dark matter halo profiles, and is favored over a null signal at 3.2 sigma significance. This result demonstrates the potential of microwave background lensing to probe the dark matter distribution in galaxy group and galaxy cluster halos.  [Show abstract] [Hide abstract]
ABSTRACT: Twopoint correlation functions of cosmic microwave background polarization provide a physically independent probe of the surprising suppression of correlations in the cosmic microwave background temperature anisotropies at large angular scales. We investigate correlation functions constructed from both the Q and U Stokes parameters and from the E and B polarization components. The dominant contribution to these correlation functions comes from local physical effects at the last scattering surface or from the epoch of reionization at high redshift, so all should be suppressed if the temperature suppression is due to an underlying lack of correlations in the cosmological metric perturbations larger than a given scale. We evaluate the correlation functions for the standard ΛCDM cosmology constrained by the observed temperature correlation function, and compute statistics characterizing their suppression on large angular scales. Future fullsky polarization maps with minimal systematic errors on large angular scales will provide strong tests of whether the observed temperature correlation function is a statistical fluke or reflects a fundamental shortcoming of the standard cosmological model.  [Show abstract] [Hide abstract]
ABSTRACT: We measure the crosscorrelation of cosmic microwave background lensing convergence maps derived from Atacama Cosmology Telescope data with galaxy lensing convergence maps as measured by the CanadaFranceHawaii Telescope Stripe 82 Survey. The CMBgalaxy lensing cross power spectrum is measured for the first time with a significance of 3.2{\sigma}, which corresponds to a 16% constraint on the amplitude of density fluctuations at redshifts ~ 0.9. With upcoming improved lensing data, this novel type of measurement will become a powerful cosmological probe, providing a precise measurement of the mass distribution at intermediate redshifts and serving as a calibrator for systematic biases in weak lensing measurements. 
Article: The Atacama Cosmology Telescope: Measuring radio galaxy bias through crosscorrelation with lensing
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ABSTRACT: We correlate the positions of radio galaxies in the FIRST survey with the CMB lensing convergence estimated from the Atacama Cosmology Telescope over 470 square degrees to determine the bias of these galaxies. We remove optically crossmatched sources below redshift $z=0.2$ to preferentially select Active Galactic Nuclei (AGN). We measure the angular crosspower spectrum $C_l^{\kappa g}$ at $4.4\sigma$ significance in the multipole range $100<l<3000$, corresponding to physical scales between $\approx$ 260 Mpc at an effective redshift $z_{\rm eff}= 1.5$. Modelling the AGN population with a redshiftdependent bias, the crossspectrum is well fit by the Planck bestfit $\Lambda$CDM cosmological model. Fixing the cosmology we fit for the overall bias model normalization, finding $b(z_{\rm eff}) = 3.5 \pm 0.8$ for the full galaxy sample, and $b(z_{\rm eff})=4.0\pm1.1 (3.0\pm1.1)$ for sources brighter (fainter) than 2.5 mJy. This measurement characterizes the typical halo mass of radioloud AGN: we find $\log(M_{\rm halo} / M_\odot) = 13.6^{+0.3}_{0.4}$.  [Show abstract] [Hide abstract]
ABSTRACT: The accelerating expansion of the universe at recent epochs is encoded in the cosmic microwave background: a few percent of the total temperature fluctuations are generated by evolving gravitational potentials which trace the largescale structures in the universe. This signature of dark energy, the Integrated SachsWolfe Effect, has been detected by averaging temperatures in the WMAP sky maps corresponding to the directions of superstructures in the Sloan Digital Sky Survey data release 6. We model the maximum average peak signal expected in the standard $\Lambda$CDM cosmological model, using Gaussian random realizations of the microwave sky, including correlations between different physical contributions to the temperature fluctuations and between different redshift ranges of the evolving gravitational potentials. We find good agreement with the mean temperature peak amplitude from previous theoretical estimates based on largescale structure simulations, but with larger statistical uncertainties. We apply our simulation pipeline to four different foregroundcleaned microwave temperature maps from Planck and WMAP data, finding a mean temperature peak signal at previously identified sky locations which exceeds our theoretical mean signal at a statistical significance of about $2.5\sigma$ and which differs from a null signal at $3.5\sigma$.  [Show abstract] [Hide abstract]
ABSTRACT: Quasidilaton massive gravity offers a physically welldefined gravitational theory with nonzero graviton mass. We present the full set of dynamical equations governing the expansion history of the universe, valid during radiation domination, matter domination, and a latetime selfaccelerating epoch related to the graviton mass. The existence of selfconsistent solutions constrains the amplitude of the quasidilaton field and the graviton mass, as well as other model parameters. We point out that the effective mass of gravitational waves can be significantly larger than the graviton mass, opening the possibility that a single theory can explain both the latetime acceleration of the cosmic expansion and modifications of structure growth leading to the suppression of largeangle correlations observed in the cosmic microwave background. 
Article: The Atacama Cosmology Telescope: A Measurement of the Thermal SunyaevZel'dovich OnePoint PDF
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ABSTRACT: We present a measurement of the onepoint probability distribution function (PDF) of the thermal SunyaevZel'dovich (tSZ) decrement in the pixel temperature histogram of filtered 148 GHz sky maps from the Atacama Cosmology Telescope (ACT). The PDF includes the signal from all galaxy clusters in the map, including objects below the signaltonoise threshold for individual detection, making it a particularly sensitive probe of the amplitude of matter density perturbations, $\sigma_8$. We use a combination of analytic halo model calculations and numerical simulations to compute the theoretical tSZ PDF and its covariance matrix, accounting for all noise sources and including relativistic corrections. From the measured ACT 148 GHz PDF alone, we find $\sigma_8 = 0.793 \pm 0.018$, with additional systematic errors of $\pm 0.017$ due to uncertainty in intracluster medium gas physics and $\pm 0.006$ due to uncertainty in infrared point source contamination. Using effectively the same data set, the statistical error here is a factor of two lower than that found in ACT's previous $\sigma_8$ determination based solely on the skewness of the tSZ signal. In future temperature maps with higher sensitivity, the tSZ PDF will break the degeneracy between intracluster medium gas physics and cosmological parameters.  [Show abstract] [Hide abstract]
ABSTRACT: A period of inflation in the early universe produces a nearly scaleinvariant spectrum of gravitational waves over a huge range in wavelength. If the amplitude of this gravitational wave background is large enough to be detectable with microwave background polarization measurements, it will also be detectable directly with a spacebased laser interferometer. Using a Monte Carlo sampling of inflation models, we demonstrate that the combination of these two measurements will strongly constrain the expansion history during inflation and the physical mechanism driving it. 
Article: Dynamics of Gauge Field Inflation
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ABSTRACT: We analyze the existence and stability of dynamical attractor solutions for cosmological inflation driven by the coupling between fermions and a gauge field. Assuming a spatially homogeneous and isotropic gauge field and fermion current, the interacting fermion equation of motion reduces to that of a free fermion up to a phase shift. Consistency of the model is ensured via the Stuckelberg mechanism. We prove the existence of exactly one stable solution, and demonstrate the stability numerically. Inflation arises without fine tuning, and does not require postulating any effective potential or nonstandard coupling.  [Show abstract] [Hide abstract]
ABSTRACT: If a primordial magnetic field in the universe has nonzero helicity, the violation of parity symmetry results in nonzero correlations between cosmic microwave background temperature and Bmode polarization. In this paper we derive approximations to the relevant microwave background power spectra arising from a helical magnetic field. Using the crosspower spectrum between temperature and Bmode polarization from the WMAP nineyear data, we set a 95\% confidence level upper limit on the helicity amplitude to be 10 nG$^2$ Gpc for helicity spectral index $n_H = 1.9$, for a cosmological magnetic field with effective field strength of 3 nG and a powerlaw index $n_B = 2.9$ near the scaleinvariant value. Future microwave background polarization maps with greater sensitivity will be able to detect the helicity of an inflationary magnetic field well below the maximum value allowed by microwave background constraints on the magnetic field amplitude.  [Show abstract] [Hide abstract]
ABSTRACT: Future arcminute resolution polarization data from groundbased Cosmic Microwave Background (CMB) observations can be used to estimate the contribution to the temperature power spectrum from the primary anisotropies and to uncover the signature of reionization near $\ell=1500$ in the small angularscale temperature measurements. Our projections are based on combining expected smallscale Emode polarization measurements from Advanced ACTPol in the range $300<\ell<3000$ with simulated temperature data from the full Planck mission in the low and intermediate $\ell$ region, $2<\ell<2000$. We show that the six basic cosmological parameters determined from this combination of data will predict the underlying primordial temperature spectrum at high multipoles to better than $1\%$ accuracy. Assuming an efficient cleaning from multifrequency channels of most foregrounds in the temperature data, we investigate the sensitivity to the only residual secondary component, the kinematic SunyaevZel'dovich (kSZ) term. The CMB polarization is used to break degeneracies between primordial and secondary terms present in temperature and, in effect, to remove from the temperature data all but the residual kSZ term. We estimate a $15 \sigma$ detection of the diffuse homogeneous kSZ signal from expected AdvACT temperature data at $\ell>1500$, leading to a measurement of the amplitude of matter density fluctuations, $\sigma_8$, at $1\%$ precision. Alternatively, by exploring the reionization signal encoded in the patchy kSZ measurements, we bound the time and duration of the reionization with $\sigma(z_{\rm re})=1.1$ and $\sigma(\Delta z_{\rm re})=0.2$. We find that these constraints degrade rapidly with large beam sizes, which highlights the importance of arcminutescale resolution for future CMB surveys.
Publication Stats
6k  Citations  
619.83  Total Impact Points  
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Institutions

20112015

University of Oxford
Oxford, England, United Kingdom


20052015

University of Pittsburgh
 Physics and Astronomy
Pittsburgh, Pennsylvania, United States


20122013

University of Toronto
 Canadian Institute for Theoretical Astrophysics
Toronto, Ontario, Canada


19922006

University of Chicago
 • Department of Astronomy and Astrophysics
 • Department of Physics
Chicago, Illinois, United States 
NASA
Washington, West Virginia, United States


19992005

Rutgers, The State University of New Jersey
 Department Physics and Astronomy
New Brunswick, New Jersey, United States


1998

Tufts University
 Department of Physics and Astronomy
Georgia, United States


19951997

Harvard University
 Department of Physics
Cambridge, Massachusetts, United States


1996

HarvardSmithsonian Center for Astrophysics
Cambridge, Massachusetts, United States
