Extended Surface Photometry Toolbox

Profiling a galaxy

  1. Select the source or sources you wish to have profiled. Do this using the `Objects' tab. In this panel, press `Add source', and then drag out a circle on the image to indicate the outer limit of the profiling process. After you have added a source, you can adjust the position of a circle by dragging it, or adjust its size by dragging on the small square grip which appears on it. You can then move on to the `Ellipse Fit' tab.
  2. To delete a source, select it in the text list of sources, and press the `Delete source' button.
  3. Specify the background on your image. You can do this either by inserting the values, if you know then, or by pressing the `Estimate...' button to have the toolbox make an estimate for you.
  4. Specify an ARD file, if you want. You can use the `Image regions...' toolbox to help you here.
  5. Choose the method you wish to use to obtain the fitted ellipses. There are three possibilities: `using isophote contours', which corresponds to the ESP ELLFOU task, and works by fitting ellipses to isophote contours; `using intensity analysis', which corresponds to ELLPRO, and uses a simpler intensity-based method; or use this last method's slow variant, which should give better results at low radii.
  6. There are a number of `expert' options in this panel. The use of these options can reasonably be understood only in conjunction with the ESP documentation, SUN/180, to which you should refer for further details.

Output formats

The toolbox can produce output in two formats. The first is the more-or-less human-readable format which ESP has traditionally used: this is sent to the file named in the field `Text output'. The second is a more structured, but still largely readable, format called STL, or `small text list' (described in detail in the CAT library documentation, SUN/181). The library which writes this format requires that the output filename is restricted to alphanumeric characters plus underscore, and ends in ".txt". If you do not supply file names here, the toolbox will supply defaults.