How sensitive are final parameters on initial input parameters?
One frequent concern regarding image fitting is the fear that the initial guesses may sensitively affect the final parameters. This concern was alleviated early on in plots circulated internally which showed that the initial guesses for the effective radii for GALFIT, derived from SExtractor catalog values, bore either no correlation or had a huge scatter compared to the simulated galaxy parameters (Figure 2). Yet GALFIT converged on the known solutions in the end (compare Figure 2 with Figures 3 and 4). So insensitive is the code to initial inputs that even though they are often off by one to two orders of magnitude, especially for n=4 galaxies, the final scatter is only of order 0.1 dex. This is all the more striking when considering the fact that 50% of all the simulated objects have nearby neighbors, all of whom would also have quite crude initial parameters. The strong convergence behavior is not just in the effective radius parameter, but also for all the other free parameters. H