NGC 55, an irregular galaxy in Sculptor (Niall MacNeill)

NGC 55, an irregular galaxy in Sculptor

I came to post this today and was bemused to see that Fernando Qi Yang's lovely rendition of the same target is IOTD. I am pleased to see that his image and mine are quite similar in appearance, which is not always the case when different imagers process different data sets of the same object. He has a wider field of view, but I suspect a larger image scale compared to mine at 0.47"/pixel, although he doesn't say what it is. I congratulate him on the accolade and a fine result.
This is the wonderful galaxy NGC 55 in the constellation of Sculptor. It is actually quite close to us at a distance of about 6.5 million light years, so about 3x further away than Andromeda. Even though it is smaller than the Milky Way or Andromeda at 68,000 light years across, its proximity makes for a decent apparent diameter (32.4’ x 5.6’). In fact it has about the same width as the Moon.
It is a bit of an ugly duckling but it is one of my favourites and very well placed for Southern Hemisphere observers. It is clearly edge on, but there is a lot going on in there. I suspect that its “irregularity” is mostly because of its edge on aspect to us and that seen face on it may have a more conventional spiral shape.
The image is a 2 panel mosaic as it is just too large for my sensor and I didn't want to miss the subtle star tail on the left side of the galaxy in this image. I gathered 60 hours of data.
The galaxy has a load of Hydrogen Alpha emissions, and I have integrated the narrowband Ha data with a PixInsight narrowband script NBRGBCombination. I spent a lot of time on the Ha integration. I found that the final result is hugely influenced by the level of stretch in the Ha image. Too little and the amount of Ha is small but intense. As the stretch is increased, more of the Ha areas are incorporated, but they are reduced in intensity. In the end I combined two such images and used PixelMath maximum, to get, what I think is a really nice balance. I hope you agree.
Note the interesting bulge or thickening, just left of centre, where a sort of halo is created.
There are some really nice distant galaxies in the background if you care to take a tour.
A zoomed in version can be accessed via the mouse-over.

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Status	Advanced success
Started	...
PixInsight job	0OQAN8GSTYSQCIIO2QIX7ZHSL1RCHAS9
PixInsight queue size	n/a
PixInsight stage	TASK_LOG

RA (center)	00h15m06s.465
RA (top/left)	00h12m52s.135
RA (top/right)	00h17m19s.995
RA (bottom/right)	00h17m21s.562
RA (bottom/left)	00h12m55s.816

Dec (center)	-39°12′32″.69
Dec (top/left)	-39°26′54″.65
Dec (top/right)	-39°28′04″.12
Dec (bottom/right)	-38°57′54″.56
Dec (bottom/left)	-38°57′04″.40

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