4 galaxies in Ha narrowband: M51, M82, M101 and M106

[Menno555]

For over months now, the weather here (the Netherlands near the coast) is terrible and predictions are just as worse
So I decided to do some work with captures of last year.

I did some captures in 2021 of the stronger Ha narrowband galaxies M51, M82, M101 and M106 and reprocessed them, focusing only on that.
I did keep the apparent sizes for comparison and only now I see that M51 is really not that big in apparent size. Somehow I always felt that M51 is huge but it isn't

The 4 captures differ in number of exposures, exposure times (300 and 600sec), gain, and so on. So relative brightness is only a approximation here.
M101 is really still a work in progress though, want to add more data to that. M106 also to see if I can get some more data on the vertical arm.
No Ha was extracted, these are the RGB stacks as captured with camera and filters and then stacked with DeepSkyStacker or SiriL.

For best view, the full 6000px version (15Mb) is here: https://i.ibb.co/Bwsxxxp/narrow-galaxies.jpg

All this with:
Meade LX200 8" f/10 ACF OTA
Ioptron CEM25EC mount (no guiding)
Optolong L-eNhance filter (M82 and M106)
Optolong L-eXtreme filter (M51 and M101)
Zwo ASI071MC Pro camera

narrow-galaxiessm.jpg (438.77 KiB) Viewed 1222 times

[timh]

Hi Menno,

The L-extreme images are interesting because they show an almost 'HA only' view of the galaxies with the two filter passbands sampling maybe only 3 % of the total broadband light - so maybe 30-50x HA enriched ? These images really do highlight where all the star formation is happening.

With M106 - which is very bright in HA - I did at one time attempt to get even nearer to a true 100% HA view (being interested in getting a clear view of the two HA arms) by further 'purifying' the HA signal through subtracting out the underlying broadband red component. This meant taking a red channel broadband image and carefully subtracting it from the HA image just to the point that the stars begin to be removed - and thus leaving just the HA signal behind. It sort of worked and showed both of the HA arms much more clearly. Pixmath is very good for that sort of thing. But subtractions are often noisy and the subtraction of stars imprecise because of size disparities.

So just an idle curiosity thing (maybe a good definition of this hobby ) but since you have used two filters you might have the data to do something similar if you tried a similar subtraction of the broader L-enhance red channel from the L-extreme red channel data?

best wishes
Tim

[Menno555]

Hi Tim

Yes, the eXtreme and eNhance are indeed different. The eNhance is way "softer" and combines a lot more in neutral/white colors.
Subtracting the Ha is surely possible with combining but like you mentioned, the noise is the big spoiler here.
But gonna experiment for sure with it M106 is on my list to do with the eXtreme filter and see what it does with the vertical arms. With the eNhance only the one obvious vertical arm is showing but the second one is way more illusive because its position over the disk itself.

Menno

[timh]

Yes I agree with all of that - it's probably only an interesting thing to try on M106 and M82 - for the others not so much - just leaves red dots more or less in those cases - and it does indeed need good signal for the subtraction to not be too noisy.