ELLIPSECT: A surface brightness analysis tool for GALFIT 3

TL;DR

EllipSect computes non-parametric measurements that are not provided by GALFIT 3, including the total effective radius resulting from multi-component fits, cusp radius, and the Petrosian radius.

Abstract

EllipSect is a user-friendly analysis and measurement tool, implemented in Python, that operates on the imaging data together with the output of the widely used 2D surface-brightness fitting code GALFIT 3. It produces publication-quality figures and exportable data products to enable quantitative assessment of GALFIT 3 models and their individual components. In addition, EllipSect computes non-parametric measurements that are not provided by GALFIT 3, including the total effective radius resulting from multi-component fits, cusp radius, and the Petrosian radius. This paper provides examples and a quick guide for EllipSect.

Figures (7)

• Figure 1: Example of sky computation using the gradient method. The ring around the brightest cluster member of Abell 2029 indicates the radius used by EllipSect to compute the sky. For visualization purposes, all pixels in that elliptical ring are assigned the same numerical value corresponding to the ellipse's major-axis length.
• Figure 2: Example of cube image generated by EllipSect. The left panel shows the galaxy, the middle panel is the model, and the right panel is the residual. The user can change the color palette, brightness, and contrast.
• Figure 3: Example of EllipSect output for the cD galaxy Holm 15a and its model. It shows a seven-Gaussian component fit. The red continuous line represents the galaxy and the blue continuous line represents the multicomponent GALFIT 3 model. Each Gaussian component is shown as a dashed line and is color-coded, as indicated in the inset box at the top right. The plot shows average SB vs. radius along the major axis. The residual percentage is displayed in the bottom plot.
• Figure 4: Example of cube image generated by EllipSect for M 61 galaxy. Details for this image are the same as the caption of Figure \ref{['cube']}.
• Figure 5: Example of EllipSect multi-plot output for M 61 galaxy and its model. This figure shows multiple plots of galaxy SB and model at different angles from the major axis (the major axis is the one with $0\deg$). The error is shown on the right hand side of the multiplot. The angle in red at the top right indicates the angle measured relative to the image's Y-axis. On the other hand, the subtle grey angle at the bottom left indicates the angle measured from the major axis, starting from the top, with the major axis and the bottom plot with the minor axis.