C21 is an irregular dwarf galaxy in Canis Venati, 12 million lightyears away, 20.000 lightyears in diameter and around 30 billion sun masses heavy and thus one of the heaviest of its type. Its radio spectroscopic halo is a remarkable 200.000 lightyears across and thus 1000 times larer than the visible galaxy.
Its irregular shape is the result of the collision with its neighbour 500 milion years ago, creating hot gas and starburst areas which show up nicely in the Ha enhancements of the image.
This was a first time processing following
@Jon Rista recommendation to stay with linear data and no noise correction for as long as possible, and to process the stars together with the galaxy - and also not to create the plastic look of overdone noise reduction.
Stretching was done in ArcSinH, HistogramTrafo and GHS - the GHS version prevailed delivering the best results.
Also I used a game galaxy mask to allow lowering the background lightness a bit.
For asthetic rasons I did use a slight BlurX and tiny NoiseX at thevery end though.
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