Making maps from Planck LFI 30 GHz data with asymmetric beams and cooler noise

¹ Astrophysics Group, Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK
² Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
³ SISSA/ISAS, Via Beirut 4, 34014 Trieste, and INFN, Sezione di Trieste, via Valerio 2, 34127, Italy
⁴ Laboratoire Astroparticule & Cosmologie, 10 rue Alice Domon & Léonie Duquet, 75205 Paris Cedex 13, France (UMR 7164 – Université Paris Diderot, CEA, CNRS, Observatoire de Paris, France)
⁵ Computational Cosmology Center, Lawrence Berkeley National Laboratory, Berkeley CA 94720, USA
⁶ Space Sciences Laboratory, University of California Berkeley, Berkeley CA 94720, USA
⁷ Dipartimento di Fisica, Università di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁸ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA 91109, USA
⁹ California Institute of Technology, Pasadena CA 91125, USA
¹⁰ Warsaw University Observatory, Aleje Ujazdowskie 4, 00478 Warszawa, Poland
¹¹ Institut d'Astrophysique de Paris, 98 bis Boulevard Arago, 75014 Paris, France
¹² University of Helsinki, Department of Physics, PO Box 64, 00014 Helsinki, Finland
¹³ Helsinki Institute of Physics, PO Box 64, 00014 Helsinki, Finland e-mail: torsti.poutanen@helsinki.fi
¹⁴ INFN, Sezione di Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
¹⁵ Metsähovi Radio Observatory, Helsinki University of Technology, Metsähovintie 114, 02540 Kylmälä, Finland
¹⁶ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
¹⁷ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena CA 91125, USA
¹⁸ INAF - IASF Bologna, via P. Gobetti, 101, 40129 Bologna, Italy
¹⁹ Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana IL 61801, USA
²⁰ Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana IL 61801, USA

Received: 13 June 2008
Accepted: 3 November 2008

Abstract

The Planck satellite will observe the full sky at nine frequencies from 30 to 857 GHz. Temperature and polarization frequency maps made from these observations are prime deliverables of the Planck mission. The goal of this paper is to examine the effects of four realistic instrument systematics in the 30 GHz frequency maps: non-axially-symmetric beams, sample integration, sorption cooler noise, and pointing errors. We simulated one-year long observations of four 30 GHz detectors. The simulated timestreams contained cosmic microwave background (CMB) signal, foreground components (both galactic and extra-galactic), instrument noise (correlated and white), and the four instrument systematic effects. We made maps from the timelines and examined the magnitudes of the systematics effects in the maps and their angular power spectra. We also compared the maps of different mapmaking codes to see how they performed. We used five mapmaking codes (two destripers and three optimal codes). None of our mapmaking codes makes any attempt to deconvolve the beam from its output map. Therefore all our maps had similar smoothing due to beams and sample integration. This is a complicated smoothing, because each map pixel has its own effective beam. Temperature to polarization cross-coupling due to beam mismatch causes a detectable bias in the TE spectrum of the CMB map. The effects of cooler noise and pointing errors did not appear to be major concerns for the 30 GHz channel. The only essential difference found so far between mapmaking codes that affects accuracy (in terms of residual root-mean-square) is baseline length. All optimal codes give essentially indistinguishable results. A destriper gives the same result as the optimal codes when the baseline is set short enough (Madam). For longer baselines destripers (Springtide and Madam) require less computing resources but deliver a noisier map.