Physical Description

NGC 3184 is a fairly bright face-on round spiral galaxy in UMa located just east of Tania Australis (μ-UMa), which is one of the hind paws of the Great Bear (using the convention of the Big Dipper's handle as the tail). In Rev D you can see that it lies close to the constellation border of Leo Minor. NGC 3184 is often called the "Little Pinwheel Galaxy" due to its resemblance to the brighter and closer Pinwheel Galaxy, M101. It is approximately 7' x 7' in size with center brightness about magnitude 9.8, distance 39 Mly or 12 Mpsc, Hubble class Sc. (Ref: Sky Atlas 2000.0 Companion, 2nd Ed.)

Contained in NGC 3184 are two HII regions NGC 3180 and NGC 3181. Referring to Rev E, 3180 is the diffuse nebular structure making up the outer arm at about the 2:00 position, and 3181 at about 4:00. These regions are difficult to distinguish from the rest of the galaxy in this image but are more distinct as bright nebulous regions visually, hence they have their own NGC designations. (Ref: Wikipedia)

Imaging Notes

I had largely ignored imaging this galaxy as Stellarium lists it only as NGC 3180 with magnitude 12.68. Lately I was perusing some of Gary Imm's galaxy image collection and came across this one. I was struck with how nicely round and symmetrical it was and decided to give it some time. I'm glad I did as it turned out to be an interesting as well as photographically pleasing target.

I got a rare three clear nights in Feb 2020 near the New Moon with fairly good transparency and seeing conditions. As you can see in the Original image, the field of view contains a comparatively bright star that is quite over saturated and dominant. That is GP UMa, which actually is only magnitude 6.5. In the final image I cropped it out to focus only on the galaxy.

Ubiquitous Hardware Issues

I have yet to fully address a vibration issue caused by my FLI ML16200 cooling fan, however I did manage to mitigate it better in this imaging session. The vibration appears to be with the primary mirror. I locked it down more aggressively followed by torquing the primary focus knob in the CCW direction more so than I normally would. This seemed to help.

I discovered that my AP 1100 mount was greatly out of balance, and having addressed that, my guiding was much better. There was a failed attempt the night before this session in which my stars were greatly slanted, and thankfully this issue was greatly improved with the balancing.

But there is still evidence of optical misalignment in the C11 which I need to address. One thing I presently have missing is the ability to adjust tip-tilt in the imaging train. That may be required to make this work properly.

Processing Notes

There is quite a bit of residual noise, particularly chromatic noise, and as usual more integration time followed by even more careful processing ought to clean that up more satisfactorily. Note that this target is fairly small, as I listed at the beginning, being only some 7' x 7' in size. My resolution is about 0.44 "/px but with seeing conditions likely on the order of 1.5 - 2". I did employ a modest measure of Deconvolution in PixInsight to help deblur the image somewhat, but I did not want to dial this up too high. I did not do any sharpening as the results were unsatisfactory, but I did do a blended application of HDRMultiscaleTransform. One consolation is that I looked at an APOD (from almost 20 years ago), and the resolution and color balance of that image was actually worse than mine, so maybe I can brag that this is good APOD material after all (from two decades past).

Summary

However, even with these usual ongoing issues, I am still pleased with the outcome of this image, and I hope you enjoy it.

Revisions

Revisions F and G are from a later set of processing steps. This time I targeted a more deblured and less saturated look because I don't think this color data warrants trying to detail the dimmer portions of the galaxy.