SANEPIC: A Map-Making Method for Timestream Data From Large Arrays

We describe a map-making method which we have developed for the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) experiment, but which should have general application to data from other submillimeter arrays. Our method uses a Maximum Likelihood based approach, with several approximations, which allows images to be constructed using large amounts of data with fairly modest computer memory and processing requirements. This new approach, Signal And Noise Estimation Procedure Including Correlations (SANEPIC), builds upon several previous methods, but focuses specifically on the regime where there is a large number of detectors sampling the same map of the sky, and explicitly allowing for the the possibility of strong correlations between the detector timestreams. We provide real and simulated examples of how well this method performs compared with more simplistic map-makers based on filtering. We discuss two separate implementations of SANEPIC: a brute-force approach, in which the inverse pixel-pixel covariance matrix is computed; and an iterative approach, which is much more efficient for large maps. SANEPIC has been successfully used to produce maps using data from the 2005 BLAST flight. Subject headings: methods: data analysis — techniques: image processing — submillimeter — balloons Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada Laboratoire APC, 10, rue Alice Domon et Léonie Duquet 75205, Paris, France Department of Physics & Astronomy, Cardiff University, 5 The Parade, Cardiff, CF24 3AA, UK Jet Propulsion Laboratory, Pasadena, CA 91109-8099 Observational Cosmology, MS 59-33, California Institute of Technology, Pasadena, CA 91125 Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 Department of Physics, University of Miami, 1320 Campo Sano Drive, Carol Gables, FL 33146 Instituto Nacional de Astrof́ısica Óptica y Electrónica (INAOE), Aptdo. Postal 51 y 72000 Puebla, Mexico Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON