Robert Thornton

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

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%.

The Atacama Cosmology Telescope: a measurement of the cosmic microwave background power spectrum at 148 and 218 GHz from the 2008 southern survey

We present measurements of the cosmic microwave background (CMB) power spectrum made by the Atacama Cosmology Telescope at 148 GHz and 218 GHz, as well as the cross-frequency spectrum between the two channels. Our results clearly show the second through the seventh acoustic peaks in the CMB power spectrum. The measurements of these higher-order peaks provide an additional test of the ΛCDM cosmological model. At l>3000, we detect power in excess of the primary anisotropy spectrum of the CMB. At lower multipoles 500 < l < 3000, we find evidence for gravitational lensing of the CMB in the power spectrum at the 2.8σ level. We also detect a low level of Galactic dust in our maps, which demonstrates that we can recover known faint, diffuse signals.

Overview of the Atacama Cosmology Telescope: receiver, instrumentation, and telescope systems

The Atacama Cosmology Telescope was designed to measure small-scale anisotropies in the Cosmic Microwave Background and detect galaxy clusters through the Sunyaev-Zel’dovich effect. The instrument is located on Cerro Toco in the Atacama Desert, at an altitude of 5190 meters. A six-meter off-axis Gregorian telescope feeds a new type of cryogenic receiver, the Millimeter Bolometer Array Camera. The receiver features three 1000-element arrays of transition-edge sensor bolometers for observations at 148GHz, 218GHz, and 277GHz. Each detector array is fed by free space mm-wave optics. Each frequency band has a field of view of approximately 22 × 26. The telescope was commissioned in 2007 and has completed its third year of operations. We discuss the major components of the telescope, camera, and related systems, and summarize the instrument performance. Subject headings: Microwave Telescopes, CMB Observations

Optical design of the Atacama Cosmology Telescope and the Millimeter Bolometric Array Camera

The Atacama Cosmology Telescope is a 6 m telescope designed to map the cosmic microwave background simultaneously at 145, 215, and 280 GHz with arcminute resolution. Each frequency will have a 32 by 32 element focal plane array of transition edge sensor bolometers. The telescope and the cold reimaging optics are optimized for millimeter-wave observations with these sensitive detectors. The design of each is described.

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

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.

The Atacama Cosmology Telescope: Extragalactic Sources at 148 GHz in the 2008 Survey

We report on extragalactic sources detected in a 455 deg2 map of the southern sky made with data at a frequency of 148 GHz from the Atacama Cosmology Telescope (ACT) 2008 observing season. We provide a catalog of 157 sources with flux densities spanning two orders of magnitude: from 15 mJy to 1500 mJy. Comparison to other catalogs shows that 98% of the ACT detections correspond to sources detected at lower radio frequencies. Three of the sources appear to be associated with the brightest cluster galaxies of low-redshift X-ray-selected galaxy clusters. Estimates of the radio to millimeter-wave spectral indices and differential counts of the sources further bolster the hypothesis that they are nearly all radio sources, and that their emission is not dominated by re-emission from warm dust. In a bright (>50 mJy) 148 GHz selected sample with complete cross-identifications from the Australia Telescope 20 GHz survey, we observe an average steepening of the spectra between 5, 20, and 148 GHz with median spectral indices of α5-20 = –0.07 ± 0.06, α20-148 = –0.39 ± 0.04, and α5-148 = –0.20 ± 0.03. When the measured spectral indices are taken into account, the 148 GHz differential source counts are consistent with previous measurements at 30 GHz in the context of a source count model dominated by radio sources. Extrapolating with an appropriately rescaled model for the radio source counts, the Poisson contribution to the spatial power spectrum from synchrotron-dominated sources with flux density less than 20 mJy is C Sync = (2.8 ± 0.3) × 10–6μK2.

The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters

Author(s): Louis, T; Grace, E; Hasselfield, M; Lungu, M; Maurin, L; Addison, GE; Ade, PAR; Aiola, S; Allison, R; Amiri, M; Angile, E; Battaglia, N; Beall, JA; De Bernardis, F; Bond, JR; Britton, J; Calabrese, E; Cho, HM; Choi, SK; Coughlin, K; Crichton, D; Crowley, K; Datta, R; Devlin, MJ; Dicker, SR; Dunkley, J; Dunner, R; Ferraro, S; Fox, AE; Gallardo, P; Gralla, M; Halpern, M; Henderson, S; Hill, JC; Hilton, GC; Hilton, M; Hincks, AD; Hlozek, R; Patty Ho, SP; Huang, Z; Hubmayr, J; Huffenberger, KM; Hughes, JP; Infante, L; Irwin, K; Kasanda, SM; Klein, J; Koopman, B; Kosowsky, A; Li, D; Madhavacheril, M; Marriage, TA; McMahon, J; Menanteau, F; Moodley, K; Munson, C; Naess, S; Nati, F; Newburgh, L; Nibarger, J; Niemack, MD; Nolta, MR; Nunez, C; Page, LA; Pappas, C; Partridge, B; Rojas, F; Schaan, E; Schmitt, BL; Sehgal, N; Sherwin, BD; Sievers, J; Simon, S; Spergel, DN; Staggs, ST; Switzer, ER; Thornton, R; Trac, H; Treu, J; Tucker, C; Engelen, AV; Ward, JT; Wollack, EJ | Abstract:

Evidence of Lensing of the Cosmic Microwave Background by Dark Matter Halos

We present evidence 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 optically selected CMASS galaxies from the SDSS-III/BOSS survey. The mean lensing signal is consistent with simulated dark matter halo profiles and is favored over a null signal at 3.2σ significance. This result demonstrates the potential of microwave background lensing to probe the dark matter distribution in galaxy group and galaxy cluster halos.

The Atacama Cosmology Telescope: Calibration with the Wilkinson Microwave Anisotropy Probe using cross-correlations

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). ACTs 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.We present a new calibration method based on cross-correlations with WMAP and apply it to data from the Atacama Cosmology Telescope (ACT). ACTs 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 < ell < 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 high signal-to-noise over a wide range of multipoles.

Two-season Atacama Cosmology Telescope polarimeter lensing power spectrum

Blake D. Sherwin, Alexander van Engelen, Neelima Sehgal, Mathew Madhavacheril, 3 Graeme E. Addison, Simone Aiola, 7, 8 Rupert Allison, Nicholas Battaglia, Daniel T. Becker, James A. Beall, J. Richard Bond, Erminia Calabrese, Rahul Datta, Mark J. Devlin, Rolando Dünner, Joanna Dunkley, 4, 11 Anna E. Fox, Patricio Gallardo, Mark Halpern, Matthew Hasselfield, 18 Shawn Henderson, J. Colin Hill, Gene C. Hilton, Johannes Hubmayr, John P. Hughes, Adam D. Hincks, Renée Hlozek, Kevin M. Huffenberger, Brian Koopman, Arthur Kosowsky, 8 Thibaut Louis, Löıc Maurin, Jeff McMahon, Kavilan Moodley, Sigurd Naess, 11 Federico Nati, Laura Newburgh, Michael D. Niemack, Lyman A. Page, Jonathan Sievers, David N. Spergel, 26 Suzanne T. Staggs, Robert J. Thornton, 13 Jeff Van Lanen, Eve Vavagiakis, and Edward J. Wollack Berkeley Center for Cosmological Physics, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720 Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON, Canada M5S 3H8 Physics and Astronomy Department, Stony Brook University, Stony Brook, NY 11794 Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544 Dept. of Physics and Astronomy, The Johns Hopkins University,