The Duchamp Source Finder

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Background

A lot of radio astronomy data consist of three dimensions: two representing the position on the sky, and the third representing frequency (or wavelength, or velocity). If one is observing a particular spectral line, objects such as galaxies (if it is HI) or masers (OH, say) will appear as discrete objects in three dimensions, being constrained in spatial position and frequency coverage.

If one is conducting a survey over a reasonably large area of the sky, one will not want to search manually through the data, but instead do so in an automated and repeatable way, with well-defined selection criteria.

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Duchamp

Duchamp is a solution to this problem of three-dimensional source finding. It has the following features:

• Efficient three-dimensional searching and merging of detected objects.
• Optional noise-reduction prior to searching via the technique of wavelet reconstruction. This innovative procedure greatly enhances the detectability of fainter sources.
• Alternative use of spatial or spectral smoothing to reduce noise and enhance features.
• Ease-of-use through a simple parameter file input.
• Flexibility to control all relevant parameters such as signal-to-noise threshold or the minimum size of detections.
• A useful range of text- and graphics-based output (click on links to see examples):
  • A list of the detections and their properties, as well as the input parameters that were used. [text file]
  • Integrated spectra of each detection. [postscript file]
  • A map showing the spatial location and integrated flux of the detections. [postscript file]
  • Optional production of Karma annotation files and VOTables (XML format) for use in other programs.

Example of the spectral output of Duchamp.

Duchamp does not make assumptions about the shape of the detections -- it does not fit Gaussians or any other function to the detected objects, it simply reports their locations. Note that it has been designed for the case of small numbers of object pixels in a lot of noise (what one would expect for HI or maser surveys). As it keeps track of all detected pixels, it may not perform as efficiently for cubes with a large amount of extended emission, such as millimetre observations of molecular lines. You are welcome to try it however, and feedback is always well received.

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Why "Duchamp"?

Odd name — where does it come from? I wanted the program to have an interesting name, preferably not an acronym (so many are just too forced and dodgy...). As it is designed for data cubes, I had initially though of Picasso, after the leading cubist, but that had already been taken by Robert Minchin. So I went with Marcel Duchamp, a cubist, dadaist and surrealist artist, who pioneered the art of "readymades", or "found objects".

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