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Paper: Galapagos: A Semi-Automated Tool for Galaxy Profile Fitting
Volume: 442, Astronomical Data Analysis Software and Systems XX (ADASSXX)
Page: 155
Authors: Häußler, B.; Barden, M.; Bamford, S. P.; Rojas, A.
Abstract: When it comes to measuring galaxy parameters, e.g. sizes (half-light radii), shapes (axial ratios) or profiles (Sérsic indices), on a large sample of tens of thousands of galaxies, e.g. COSMOS, STAGES or GEMS, or even millions of galaxies, e.g. SDSS, an automated fitting routine is strongly required. In this work, we introduce GALAPAGOS (Galaxy Analysis over Large Areas: Parameter Assessment by GALFITting Objects from SEXTRACTOR), a code that enables users to carry out profile fitting on large surveys in a mostly automated manner. After initial setup and specification of a set of parameters, the code manages the whole process: source extraction (with SEXTRACTOR) on the individual survey frames, masking and deblending, setup of the galaxy fitting process (using GALFIT), the fitting itself, and finally the compilation of all the resulting parameters into an object catalog; without the need for any user interaction. We present these steps and highlight the strengths of GALAPAGOS compared to other codes used for similar purposes. We have carried out thorough tests of the current version of the code on both real and simulated data. We show results and discuss the statistical and systematic biases of fitting codes in general and GALAPAGOS in particular. We find that GALAPAGOS returns very accurate measurements of the galaxy parameters without systematic bias and with only small statistical uncertainties, at least on 1-orbit HST data and assuming an optimal setup. We also briefly present MEGAMORPH, which will open up Galapagos for various survey strategies (including ground-based with variable PSF), multi-wavelength data, Bulge/Disk decompositions and high-performance computing facilities.
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