galapagos: from pixels to parameters

Authors

  • Marco Barden,

    Corresponding author
    1. Institute of Astro- and Particle Physics, University of Innsbruck, Technikerstraße 25, A-6020 Innsbruck, Austria
    2. Max-Planck-Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
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  • Boris Häußler,

    1. Max-Planck-Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
    2. Schools of Physics & Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD
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  • Chien Y. Peng,

    1. NRC Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
    2. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
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  • Daniel H. McIntosh,

    1. Department of Physics, University of Missouri-Kansas City, 5100 Rockhill Road, Kansas City, MO 64110, USA
    2. Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003, USA
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  • Yicheng Guo

    1. Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003, USA
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E-mail: marco.barden@uibk.ac.at

ABSTRACT

To automate source detection, two-dimensional light profile Sérsic modelling and catalogue compilation in large survey applications, we introduce a new code Galaxy Analysis over Large Areas: Parameter Assessment by galfitting Objects from SExtractor (galapagos). Based on a single set-up, galapagos can process a complete set of survey images. It detects sources in the data, estimates a local sky background, cuts postage stamp images for all sources, prepares object masks, performs Sérsic fitting including neighbours and compiles all objects in a final output catalogue. For the initial source detection, galapagos applies SExtractor, while galfit is incorporated for modelling Sérsic profiles. It measures the background sky involved in the Sérsic fitting by means of a flux growth curve. galapagos determines postage stamp sizes based on SExtractor shape parameters. In order to obtain precise model parameters, galapagos incorporates a complex sorting mechanism and makes use of modern CPU’s multiplexing capabilities. It combines SExtractor and galfit data in a single output table. When incorporating information from overlapping tiles, galapagos automatically removes multiple entries from identical sources. galapagos is programmed in the Interactive Data Language (idl). We test the stability and the ability to properly recover structural parameters extensively with artificial image simulations. Moreover, we apply galapagos successfully to the STAGES data set. For one-orbit Hubble Space Telescope data, a single 2.2-GHz CPU processes about 1000 primary sources per 24 h. Note that galapagos results depend critically on the user-defined parameter set-up. This paper provides useful guidelines to help the user make sensible choices.

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