A MORPHOLOGICAL FILTER FOR REMOVING CIRRUS-LIKE EMISSION FROM FAR-INFRARED EXTRAGALACTIC IRAS FIELDS

The presence of diffuse extended IR emission from the Galaxy in the fo rm of the so called ''Galactic Cirrus'' emission has hampered the expl oration of the extragalactic sky at long IR wavelengths. We describe t he development of a filter based on mathematical morphology which appe ars to be a promising approach to the problem of cirrus removal. The m ethod of Greyscale Morphology was applied to a lambda100 mum IRAS imag e of the M81 group of galaxies. This is an extragalactic field which s uffers from serious contamination from foreground Galactic ''cirrus.'' Using a technique called ''sieving,'' it was found that the cirrus em ission has a characteristic behavior which can be quantified in terms of an average spatial structure spectrum or growth function. This func tion was then used to attempt to remove ''cirrus'' from the entire ima ge. The result was a significant reduction of cirrus emission by an in tensity factor of 15 compared with the original input image. The metho d appears to preserve extended emission in the spatially extended IR d isks of M81 and M82 as well as distinguishing fainter galaxies within bright regions of galactic cirrus. The method is still under developme nt and some problems still remain to be solved. The techniques may als o be applicable to IR databases obtained with the Cosmic Background Ex plorer (COBE).