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John, thanks for displaying the H-alpha bandpass image.
The bar of NGC 253 is only hinted at in broadband optical light (e.g. R or G or B bands, or photometric U, B, V, R), yet this galaxy is quite obviously a barred spiral in your Ha image!
(putting various bands together makes for a pretty picture, but each individual band is probably more informative from the point of view of science.....)
There is obviously still some stellar continuum light in your Ha image, but the nebulae are obvious. I think that your image probably shows H-alpha maxima along the two leading edges of the bar, and that this might be the signature of shocks in which the interstellar gas is compressed into star formation along the leading edge of the bar.
I got quite a buzz from your Ha image...it is better than many of the science images of NGC 253 that have been made in the Ha bandpass!
The overall structure of this galaxy is a lot clearer in Ha than it is in a broader bandpass......it is almost as if you had made an "X-ray" of this galaxy in order to show its most important features.
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