MULTI-SCALE CLEAN: A COMPARISON OF ITS PERFORMANCE AGAINST CLASSICAL CLEAN ON GALAXIES USING THINGS

A practical evaluation of the multi-scale clean algorithm is presented. The data used in the comparisons are taken from The H I Nearby Galaxy Survey. The implementation of multi-scale clean in the CASA software package is used, although comparisons are made against the very similar multi-resolution clean algorithm implemented in AIPS. Both are compared against the classical clean algorithm (as implemented in AIPS). The results of this comparison show that several of the well-known characteristics and issues of using classical clean are significantly lessened (or eliminated completely) when using the multi-scale clean algorithm. Importantly, multi-scale clean significantly reduces the effects of the clean bowl that is caused by missing short-spacings, and the pedestal of low-level un-cleaned flux (which affects flux scales and resolution). Multiscale clean can clean down to the noise level without the divergence suffered by classical clean. We discuss practical applications of the added contrast provided by multi-scale clean using two selected astronomical examples: Hi holes in the interstellar medium and anomalous gas structures outside the main galactic disk.