Figure: Description of the HI rogues gallery

The various panels are described here. The simplest involves a greyscale representation of the optical image on the left, and the optical image with HI column density contours on the right.

When the faint optical structure warrants it, we present two representations of the optical data with different "depths" (the image on the right allows to see much fainter structures, but saturates in the center), in addition to the optical image with HI contours superimposed.

Finally, when the complexity of the HI structure warrants it, we also present a greyscale representation of the integrated HI emission. These images show clearly HI minima and maxima, which may be ambiguous in the contour maps. When we do show a greyscale map of the HI, we sometimes include contours. These are most often single contours from the optical data. When there are multiple contours, these are spaced by factors of ten apart. On a few occasions we show HI contours upon the HI greyscales. Since the HI and optical morphologies are so different, it should be obvious what the contours represent.

Credit: John Hibbard, NRAO

http://www.nrao.edu/astrores/HIrogues/webGallery/RoguesGallery06.html