Sample Selection and Processing Methods

The four galaxies shown in Figure 1 were all selected from a single scan in the SA57 polar field. As you can see, they were selected to represent a range of parameters from the 2MASS dataset. Unfortunately there were not many edge-on galaxies in this dataset for testing of the position angle. There are a couple of fairly bright galaxies (1869; NGC 4971), one with a star nearby (1585), a small faint one (1062), and a very distorted galaxy (1795; VV841).

The IRAF ellipse fitting routine, which is part of STSDAS, was used to determine the photometry of galaxies to be compared with the determinations made by GALWORKS. The fitting routine allows one to fix any of the ellipse parameters (galaxy center, ellipticity, and position angle) and determine the photometry of the galaxy. The other option is to let IRAF select the ellipse parameters at each step (you can define the step size). GALWORKS, on the other hand, determines the ellipse parameters at the 3-sigma level and holds them fixed at every step.