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Downloaded E E E From APJS, 191:423–438,2010 DECEMBER Preprint typeset using LATEX style emulateapj v. 11/10/09 THE ATACAMA COSMOLOGY TELESCOPE (ACT): BEAM PROFILES AND FIRST SZ CLUSTER MAPS A. D. HINCKS1, V. ACQUAVIVA2,3 ,P.A.R.ADE4 , P. AGUIRRE5,M.AMIRI6,J.W.APPEL1,L.F.BARRIENTOS5,E.S.BATTISTELLI7,6, J. R.BOND8 ,B.BROWN9,B.BURGER6,J.CHERVENAK10,S.DAS11,1,3 ,M.J.DEVLIN12,S.R.DICKER12,W.B.DORIESE13, J. DUNKLEY14,1,3 ,R.DÜNNER5, T. ESSINGER-HILEMAN1,R.P.FISHER1,J.W.FOWLER1,A.HAJIAN8,3,1 ,M.HALPERN6, M. HASSELFIELD6,C.HERNÁNDEZ-MONTEAGUDO15,G.C.HILTON13,M.HILTON16,17 ,R.HLOZEK14,K.M.HUFFENBERGER18, D. H. HUGHES19,J.P.HUGHES2,L.INFANTE5,K.D.IRWIN13,R.JIMENEZ20,J.B.JUIN5 ,M.KAUL12,J.KLEIN12,A.KOSOWSKY9, J. M. LAU21,22,1 ,M.LIMON23,12,1 , Y.-T. LIN24,3,5 ,R.H.LUPTON3, T. A. MARRIAGE25,3 ,D.MARSDEN12 ,K.MARTOCCI26,1 , P. MAUSKOPF4, F. MENANTEAU2,K.MOODLEY16,17 ,H.MOSELEY10,C.B.NETTERFIELD27,M.D.NIEMACK13,1,M.R.NOLTA8,L.A.PAGE1, L. PARKER1,B.PARTRIDGE28,H.QUINTANA5,B.REID20,1 ,N.SEHGAL21,J.SIEVERS8,D.N.SPERGEL3, S.T.STAGGS1,O.STRYZAK1, D.S. SWETZ12,13,E.R.SWITZER26,1,R.THORNTON12,29 ,H.TRAC30,3 ,C.TUCKER4,L.VERDE20,R.WARNE16,G.WILSON31, E. WOLLACK10, AND Y. ZHAO1 1 Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544, USA 2 Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8019, USA 3 Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544, USA 4 School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, Wales CF24 3AA, UK 5 Departamento de Astronomía y Astrofísica, Facultad de Física, Pontificía Universidad Católica de Chile, Casilla 306, Santiago 22, Chile 6 Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z4, Canada 7 Department of Physics, University of Rome “La Sapienza”, Piazzale Aldo Moro 5, I-00185 Rome, Italy 8 Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8, Canada 9 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA 10 Code 553/665, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA 11 Berkeley Center for Cosmological Physics, LBL and Department of Physics, University of California, Berkeley, CA 94720, USA 12 Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104, USA 13 NIST Quantum Devices Group, 325 Broadway Mailcode 817.03, Boulder, CO 80305, USA 14 Department of Astrophysics, Oxford University, Oxford OX1 3RH, UK 15 Max Planck Institut für Astrophysik, Postfach 1317, D-85741 Garching bei München, Germany 16 Astrophysics and Cosmology Research Unit, School of Mathematical Sciences, University of KwaZulu-Natal, Durban, 4041, South Africa 17 Centre for High Performance Computing, CSIR Campus, 15 Lower Hope Street, Rosebank, Cape Town, South Africa 18 Department of Physics, University of Miami, Coral Gables, FL 33124, USA 19 Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), Tonantzintla, Puebla, Mexico 20 ICREA & Institut de Ciencies del Cosmos (ICC), University of Barcelona, Barcelona 08028, Spain 21 Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305-4085, USA 22 Department of Physics, Stanford University, Stanford, CA 94305-4085, USA 23 Columbia Astrophysics Laboratory, 550 West 120th Street, Mail Code 5247, New York, NY 10027, USA 24 Institute for the Physics and Mathematics of the Universe, The University of Tokyo, Kashiwa, Chiba 277-8568, Japan 25 Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore 21218-2686, MD 26 Kavli Institute for Cosmological Physics, Laboratory for Astrophysics and Space Research, 5620 South Ellis Ave., Chicago, IL 60637, USA 27 Department of Physics, University of Toronto, 60 Street George Street, Toronto, ON M5S 1A7, Canada 28 Department of Physics and Astronomy, Haverford College, Haverford, PA 19041, USA 29 Department of Physics, West Chester University of Pennsylvania, West Chester, PA 19383, USA 30 Harvard-Smithsonian Center for Astrophysics, Harvard University, Cambridge, MA 02138, USA and 31 Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA Submitted 2009 June 19; accepted 2010 November 3; published 2010 December 2 ABSTRACT The Atacama Cosmology Telescope (ACT) is currently observing the cosmic microwave background with ar- arXiv:0907.0461v3 [astro-ph.CO] 6 Dec 2010 cminute resolution at 148GHz, 218GHz, and 277GHz. In this paper, we present ACT’s first results. Data have been analyzed using a maximum-likelihood map-making method which uses B-splines to model and remove the atmospheric signal. It has been used to make high-precision beam maps from which we determine the experiment’s window functions. This beam information directly impacts all subsequent analyses of the data. We also used the method to map a sample of galaxyclusters via the Sunyaev-Zel’dovich (SZ) effect, and show five clusters previously detected with X-ray or SZ observations. We provide integrated Compton-y measurements for each cluster. Of par- ticular interest is our detection of the z =0.44 component of A3128 and our current non-detectionof the low-redshift part, providing strong evidence that the further cluster is more massive as suggested by X-ray measurements. This is a compelling example of the redshift-independent mass selection of the SZ effect. Subject headings: cosmic background radiation – cosmology: observations – galaxies: clusters: general – methods: data analysis 2 HINCKS ET AL. 1. INTRODUCTION and radial profiles; window functions are derived in Section 4; A new generation of experiments is measuring the cosmic mi- Section 5 shows a selection of clusters imaged with the mapper; crowave background (CMB) at arcminute resolutions. Within and we conclude in Section 6. the past year alone, results from the South Pole Telescope (Staniszewski et al. 2009), ACBAR (Reichardt et al. 2009a), 2. THE COTTINGHAM MAPPING METHOD AMiBA (Umetsu et al. 2009), APEX-SZ (Reichardt et al. In this section, we present a technique for removing the atmo- 2009b), the Cosmic Background Imager (Sievers et al. 2009), spheric power first described by Cottingham (1987) and used the Sunyaev-Zel’dovich Array (Sharp et al. 2010), and QUaD by Meyer et al. (1991), Boughn et al. (1992), and Ganga et al. (Friedman et al. 2009) have revealed the ∼arcminute structure (1993). The temporal variations in atmospheric signals are mod- of the CMB with higher precision than ever. The angular power eled using B-splines, a class of functions ideal for interpola- spectrum of temperature fluctuations at these scales (ℓ & 1000) tion, discussed more below. The technique computes maximum- will further constrain models of the early universe. Furthermore, likelihood estimates of both the celestial and the atmospheric secondary features such as the Sunyaev-Zel’dovich (SZ) effect signals, using all available detectors in a single frequency band. and gravitational lensing probe the growth of structure. We refer to it hereafter as the Cottingham method. With its first science release, the Atacama Cosmology Tele- In the following subsections, we give a mathematical descrip- scope (ACT) now adds to these endeavors. A 6m, off-axis Gre- tion of the Cottingham method (Section 2.1), followed by a gorian telescope, it was commissioned on Cerro Toco in north- discussion of its benefits and a comparison to the “destriping” ern Chile in 2007 October. Its current receiver is the Millimeter method developed for Planck, which has close similarities (Sec- Bolometer Array Camera (MBAC), containing three 32×32 ar- tion 2.2). Our approach for including the effects of spatial vari- rays of transition edge sensor (TES) bolometers observing at ability across the detector arrays is in Section 2.3. We discuss central frequencies of 148GHz, 218GHz, and 277GHz, with the use of B-splines in Section 2.4, and finish by outlining our beam full-widths at half-maxima (FWHM) of 1.′37, 1.′01, and implementation of the method (Section 2.5) and map-making 0.′91, respectively (see Section 3.2, below). It has operated for steps (Section 2.6). three seasons and is currently in its fourth season. In 2007 one month of science observations was made using only the 2.1. The Algorithm 148GHz array. The other two frequencies were added for the 2008 season, which lasted about 3.5 months. The telescope op- The measured timestream d is modeled as a celestial signal tical design is described in Fowler et al. (2007). Hincks et al. plus an atmospheric component: (2008) and Switzer et al. (2008) report on the telescope perfor- mance and provide an overview of hardware and software sys- d = Pm + Bα + n, (1) tems. The MBAC design and details of TES detector proper- ties and readout are in Niemack (2006), Marriage et al. (2006), where the pointing matrix P projects the celestial map m into Battistelli et al. (2008), Niemack et al. (2008), Swetz et al. the timestream, B is a matrix of basis functions with amplitudes (2008), Thornton et al. (2008), and Zhao et al. (2008).32 α which model the temporal variation of atmospheric power, ACT is located at one of the premier sites for millimeter as- and n is the noise. The timestream of measurements d may be tronomy because of the high altitude (5200m) and the dry at- a concatenation of multiple detectors if they have been properly mosphere. The precipitable water vapor (PWV) had a median treated for relative gain differences. Throughout this paper, this value of 0.56mm during the nights of our 2008 season. Never- is the case: all working detectors from one frequency band are theless, atmospheric emission remains the largest signal external processed simultaneously.
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