GALAPAGOS, a semi-automated tool for galaxy profile fitting

Haeussler, Boris

When it comes to measuring galaxy parameters, e.g. sizes (half-light radii), shapes (axial ratios) or profiles (sersic indices), on a large sample of galaxies with tens of thousands or even millions of galaxies, an automated fitting routine is strongly required. In this talk, I will introduce GALAPAGOS (Galaxy Analysis over Large Areas: Parameter Assessment by GALFITting Objects from SExtractor; Barden et al, in prep), a code that enables users to carry out profile fitting on large surveys in a largely automated manner. After an initial setup and specification of a handful of parameters, the code runs the whole process: source extraction (with SExtractor) on the individual survey frames, masking and deblending, setup of the galaxy fitting process (using GALFIT; Peng at al. 2002), the fitting itself, and finally the compilation of all the resulting parameters into an object catalog; without the need for any user interaction. I will briefly present these steps and will highlight the strengths of GALAPAGOS compared to other codes used for similar purposes. I will also briefly discuss our plans for further features in the code, opening it up for varied survey strategies and multi-wavelength data.

We have carried out thorough tests of the current version of the code on both real and simulated data. I will show some 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.

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