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Title:
GEMS: Galaxy Fitting Catalogs and Testing Parametric Galaxy Fitting Codes: GALFIT and GIM2D
Authors:
Häussler, Boris; McIntosh, Daniel H.; Barden, Marco; Bell, Eric F.; Rix, Hans-Walter; Borch, Andrea; Beckwith, Steven V. W.; Caldwell, John A. R.; Heymans, Catherine; Jahnke, Knud; Jogee, Shardha; Koposov, Sergey E.; Meisenheimer, Klaus; Sánchez, Sebastian F.; Somerville, Rachel S.; Wisotzki, Lutz; Wolf, Christian
Affiliation:
AA(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany.), AB(Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003.), AC(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany.), AD(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany.), AE(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany.), AF(Astronomisches Recheninstitut, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany.), AG(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218.; Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218.), AH(University of Texas, McDonald Observatory, Fort Davis, TX 79734.), AI(Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada.), AJ(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany.), AK(University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259.), AL(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany.), AM(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany.), AN(Centro Astronomico Hispano Aleman de Calar Alto, C/Jesus Durban Remon 2-2, Almeria E-04004, Spain.), AO(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany.), AP(Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany.), AQ(Department of Physics, Denys Wilkinson Building, University of Oxford, Keble Road, Oxford OX1 3RH, UK.)
Publication:
The Astrophysical Journal Supplement Series, Volume 172, Issue 2, pp. 615-633. (ApJS Homepage)
Publication Date:
10/2007
Origin:
UCP
ApJ Keywords:
Catalogs, Galaxies: General, Galaxies: Photometry, Galaxies: Statistics, Methods: Data Analysis, Surveys
DOI:
10.1086/518836
Bibliographic Code:
2007ApJS..172..615H

Abstract

In the context of measuring the structures of intermediate-redshift galaxies with HST ACS surveys, we tune, test, and compare two widely used fitting codes (GALFIT and GIM2D) for fitting single-component Sérsic models to both simulated and real galaxy data. Our study focuses on the GEMS survey with the sensitivity of typical HST survey data, and we include our final catalog of fit results for all 41,495 objects detected in GEMS. Using simulations, we find that fitting accuracy depends sensitively on galaxy profile shape. Exponential disks are well fit and have small measurement errors, whereas fits to de Vaucouleurs profiles show larger uncertainties owing to the large amount of light at large radii. Both codes provide reliable fits with little systematic error for galaxies with effective surface brightnesses brighter than that of the sky; the formal uncertainties returned by these codes significantly underestimate the true uncertainties (as estimated using the simulations). We find that GIM2D suffers significant systematic errors for spheroids with close companions owing to the difficulty of effectively masking out neighboring galaxy light; there appears to be no work-around to this important systematic in GIM2D's current implementation. While this crowding error affects only a small fraction of galaxies in GEMS, it must be accounted for in the analysis of deeper cosmological images or of more crowded fields with GIM2D. In contrast, GALFIT results are robust to the presence of neighbors because it can simultaneously fit the profiles of multiple companions as well as the galaxy of interest. We find GALFIT's robustness to nearby companions and factor of >~20 faster runtime speed are important advantages over GIM2D for analyzing large HST ACS data sets.

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