The Atacama Cosmology Telescope (act): Beam Profiles and First Sz Cluster Maps

The Atacama Cosmology Telescope (ACT) is currently observing the cosmic microwave background with arcminute resolution at 148 GHz, 218 GHz, and 277 GHz. 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 galaxy clusters via the Sunyaev-Zel’dovich (SZ) effect, and show eight clusters previously detected in the X-ray or SZ and two new cluster candidates. We provide integrated Compton-y measurements for each cluster. Of particular interest is our detection of the z = 0.44 component of Abell 3128 and our current non-detection of 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 microwave background – cosmology: observations – galaxies: clusters: general – methods: data analysis 1 Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ, USA 08544 2 Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ USA 08544 3 Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA, USA 19104 4 Department of Physics & Astronomy, Cardiff University, 5 The Parade, Cardiff, Wales, UK CF24 3AA 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, Canada V6T 1Z4 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, Canada M5S 3H8 9 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, USA 15260 10 Code 553/665, NASA/Goddard Space Flight Center, Greenbelt, MD, USA 20771 11 NIST Quantum Devices Group, 325 Broadway Mailcode 817.03, Boulder, CO, USA 80305 12 Department of Astrophysics, Oxford University, Oxford, UK OX1 3RH 13 Max Planck Institut für Astrophysik, Postfach 1317, D-85741 Garching bei München, Germany 14 Astrophysics and Cosmology Research Unit, School of Mathematical Sciences, University of KwaZulu-Natal, Durban, 4041, South Africa 15 Centre for High Performance Computing, CSIR Campus, 15 Lower Hope St. Rosebank, Cape Town, South Africa 16 Southern African Astronomical Observatory, Observatory Road, Observatory 7925, South Africa 17 Department of Physics, University of Miami, Coral Gables, FL, USA 33124 18 Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), Tonantzintla, Puebla, Mexico 19 Deptartment of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8019