Tidal streams in the Southern Pinwheel

[marco]

Dear all, here is my latest effort, latest in term of processing since this is clearly a spring object :D

This shot is about one of the most common targets for the period, M83, the southern pinwheel. But I tried to show something less common on this one.

All started when I composed the luminance channel of this shot. Usually one of the first things I do as I start a processing is to perform a hyper stretch (gaussian) of the original fits looking for the faintest details recorded as well as possible defects. On this luminance I noticed almost immediately the faint arc north of the galaxy :confused2:. A quick search on the web turned out it was a known features, first imagined by Malin and than by (very) few others. There is a debate at the moment about its origin, perhaps it is a tidal stream remaining from a former interaction with another galaxy (long gone) or as being one of the very faintest arms of this spiral, somehow a little bit brighter in that position. I found no sure answer about the right answer.:rolleyes:

Surprisingly I found only another shot taken by an amateur showing traces of it, the beautiful one taken by Mike and posted on this web some time ago.

I hope so to contribute to the topic with my image :D

Here is the link:
http://www.glitteringlights.com/Images/deepsky/13667287_YtYhj#1420364184_vHKgwNm-A-LB

I strongly recommend to check the high res version, 4000x4000 and visible full screen with the usual zoomify page:
http://astrosurf.com/lorenzi/ccd/m83_HaLRGB

You can indeed dive into the field, there are dozen and dozen of background galaxies.

I had to stretch really a lot to show the tidal stream and the outer arms of M83, furthermore I opted to keep the background a little bit brighter than I usual do in order to help the overall visibility. I didn't see so far many pics around showing the great extend of m83, that is pretty amazing!

I also tried my best to keep the image looking natural, although at this "extreme" processing I am not sure to have succeed..:screwy:

I also added some Ha to increase the visibility of the HII regions.

I hope you will like it :rolleyes:

Clear Skies
Marco

[Octane]

That is just so stunningly beautiful.

Another masterpiece.

Awesome work, my friend.

H

[TrevorW]

Very nice indeed, well done

[strongmanmike]

Interesting result Marco, I can see why you are uming and are'ing on the image

The thing I found difficult when I went deep (and wide) on this galaxy was trying to show the tidal stream at the same level of believability as the galaxy in a natural RGB form without effectively painting it in somehow by careful use of PS tools and the heavy blurring required to hide the stretch induced noise gave an unnatural look etc... but to me this wan't reality so I opted to only showcase the tidal stream in a straight high contrast stretch (http://www.pbase.com/strongmanmike2002/image/132837742/original) ala David Malin because this was more real to me and not enhanced on a feature specific level.

As you can see there is also a faint short extension at the bottom of the over exposed main halo in the straight contrast enhanced version (both mine and David Malins) that doesn't really appear on your naturalised image even though the upper brightest arc is very well rendered...and I imagine this is becasue you haven't specifically worked on that feature to show it in the final work..?

Feature specific manipulation produces a record of sorts and certainly shows the location of a faint feature but I am in two minds as to what the achievement is and how accurate the record is...?

That said, it is still a revealing shot :thumbsup:

Mike

[marco]

Thanks H :)



Thanks Trevor :)

Clear Skies
Marco

[marco]

Hi Mike, Thanks :)

I understand your comments and this is quite an important point, since it is about defining the border between processing and making artifacts (or worse adding details not present in the image!).

I was aware about the presence of a second faint arm on the bottom part, the point is.. it is not visible in my image!

http://www.astrosurf.com/lorenzi/ccd/M83_L_gaussian.jpg

If you check this link you can see the gaussian stretch of the central part of my luminance (color added little info to this).

Apart for the ugliness and several cosmetics defects of the sensor (see the bands I had to remove manually due to a defective column close the sensor :shrug:) you can see that there is evident record of the upper arm but no trace of the lower one, or at least nothing I could honestly consider an actual detail :question:.

So you can see my effort to increase the visibility of the visible arm, but I could not enhance something that was actually not there :shrug: *That* is what I cannot consider acceptable (read=cheating)!

So it seems that we opted for two different processes but that your image is still a bit deeper (unless the arm or stream changed recently :D).

Thanks for pointing this out :)

Clear Skies
Marco

[strongmanmike]

Actually the lower extension is indeed there in your mega stretched image (can't you see it?)...you just haven't worked on it to bring it out in the final work :shrug:...here in lies the problem of feature specific enhancement.

As I said, still a very cool image :thumbsup:

Mike

[strongmanmike]

Oh and it was also good to confirm by looking at your images that the strange dark halo around the galaxy is not a processing artifact. When I noticed it in my images I couldn't for the life of me work out what was going on..? Could it be a trick of the eye and actually a chance alignment of stars in a circle around the galaxy causing the halo effect...?

Mike

[gregbradley]

Yes I wondered about that dark halo top half right side.

I have seen it on my images as well but seemed to stand out on Marcos more.

Perhaps that was the path the other galaxy took when it sideswiped M83.

Great shot Marco and well done on doing the long exposure needed to bring that out.

Greg.

[iceman]

Stunning image Marco, magnificent!

[jjjnettie]

Spectacular!

[Stevec35]

A great M83 to be sure. Love the colour and everything else.

Cheers

Steve

[multiweb]

That's very cool Marco. I realise that those tidal streams are extremely faint compared to the galaxy RGB but I think you've done a great job at blending the whole field. The luminosity is just right and the whole dynamic very well balanced. In the end it makes for a very pleasing picture. :thumbsup:

[Peter Ward]

Ditto.:thumbsup:

[marco]

Err.. you lost me here, can you point me on which feature are u referring to?



Thanks Mike



Thanks JJJinette



Thanks Steve



Thanks Marc



Thanks Peter

Clear Skies
Marco

[strongmanmike]

It looks like the galaxy is sitting in a dark hole about twice its diameter

It's pretty clear in these 100% res crops:

1) http://www.pbase.com/strongmanmike2002/image/132836997/original

2) http://www.pbase.com/strongmanmike2002/image/132836998/original

open them and then shrink to fit on your screen to make it more obvious.

I see the same dark hole/halo around your M83 too

As I said I'm starting to think it is a visual illusion created by the stars..??

Mike

[atalas]

Great shot.

[MGTechDVP]

Fantastic image, well done.

[gregbradley]

Is it possible its evidence of dark matter?

It was the first thing I noticed about Marco's image that there is a dark band around the galaxy. At first I thought it may have been processing from a lassoo. But I think its an actual thing in the image. I see it in my own images of the area.

Greg.

[RobF]

Absolutely stunning. Benchmark image - thanks for sharing with us Marco.

[marco]

Now it is clear. I have no PS at the moment handy to check the actual values of the background in different locations (am still at work), but at first impression it seems there is a kind of ring of brighter stars around the galaxy (in particular at the right) so I would go as well for a kind of visual impression. A quick check with PS or other imaging tools should give however a more "scientific" answer :)



Thanks Louie



Thanks Mariusz



it is a clear sign of the dark side of the force :D
FYI, I never use lassos to process image luminosity to avoid what Mike reported below, at least not at the initial stages. What usual I do is to duplicate the image as new layer, apply the correction I want (denoise, luminosity, etc) and than masking this layer with a Layer masks using the same base image as actual mask. The effect of the processing can than be changed by working on the mask (changing its contrast by using levels or its blending by applying a gaussian filter). That means that this usually apply to the whole image. In some limited cases (e.g. this one) I than mask (again through layer masks) the effect I had to limit the strength on certain areas. Working on specific areas with Lassos is usually not good since can easily produce less natural blends..



Thanks Rob

Marco

[Leonardo70]

Fantastic work Marco. Stunning image.
Milion galaxies on background .

Ciao,
Leo

[Ross G]

An amazing and unique photo Marco.

Thank you.

Ross.

[jase]

Lovely Marco. You've certainly gone deep to pick out the arc. Interesting discussion on processing to enhance it. I would have probably used an object mask to selectively stretch the data and keep in in line with the other image elements. Too many ways to skin a cat one could say. Ironically its not scientifically accurate due to non linear stretches. Perhaps you could do a negative linearly stretched version and superimpose the RGB galaxy over the top. In any case, its a great image. Well done.

[marco]

Thanks Leo



Thanks Ross



Thanks Jase. Yes definitely there are several ways to work out on faint details. Actually, when details are really barely visible on the original image is when things become tricky. I also recently purchased Pixinsight and I am experimenting with some of its routines, same for CCDStack. Perhaps I will be able to find other ways to squeeze out the original data. For sure this is the most stretched image I have ever produced, I usually don't like to go so extreme but I wanted to try something out of the common path on this very popular subject. Superimpose the RGB galaxy over the negative stretched data is the way Mike chose for his excellent shot, it is definitely a nice way to go and perhaps more "scientific" but I am still intrigued to experiment something different, at the end of the day my target is to have a pleasant image, with real details but not necessary scientifically accurate. A simple DDP is already producing a non scientifically accurate image, let's apart working on colors or adding narrowband images ;)

Clear Skies
Marco

[gregbradley]

it is a clear sign of the dark side of the force :D
FYI, I never use lassos to process image luminosity to avoid what Mike reported below, at least not at the initial stages. What usual I do is to duplicate the image as new layer, apply the correction I want (denoise, luminosity, etc) and than masking this layer with a Layer masks using the same base image as actual mask. The effect of the processing can than be changed by working on the mask (changing its contrast by using levels or its blending by applying a gaussian filter). That means that this usually apply to the whole image. In some limited cases (e.g. this one) I than mask (again through layer masks) the effect I had to limit the strength on certain areas. Working on specific areas with Lassos is usually not good since can easily produce less natural blends..


I agree. lasso is not such a great tool really. It has its moments but really once you start using hide all layer masks or inverted layer masks it seems a bit crude.

I have also seen this effect of a darker ring around luminance images of galaxies occassionally in my own images. It is a definite "thing".
If the theory of dark matter is in fact true and I for one feel it probably is (perhaps it is simply old spent energy particles that are black, like soot for example) , then it would make sense that these dark matter or dark energy clouds would be further out being spent particles rather than further in where more energetic particles would tend to gravitate together. Just a theory. Perhaps we should collect some images that show this effect and send it off to someone at NASA or somewhere.

Greg.



Thanks Rob

Marco[/QUOTE]

[p1taylor]

Marco you have really created a stunning image keep up the good work.

peter

[SkyViking]

That's a superb image Marco, I really like these ultra deep views.
Great processing with well balanced colours and a nice natural look overall - and that faint outer arm looks amazing :eyepop:
Thanks for the view :)

[John Hothersall]

What a sight to see all that extra dynamic usually unseen. Thanks for showing.

John.

[cookie8]

Marco,I don't know much about DSO imaging but I know a spectacular galaxy when I see one. Deserves a big WOW!

[Ken Crawford]

Very nice Marco, Deep and wonderful colors.

I showed an example of this proposed stream at AAIC that I took while at Moorook. Along with it was a shot taken at of it by the VLT to help determine if it is a stream or not. It is faint but I was able to capture it a couple of years ago with around 4 hours of exposure so I am surprised it does not show up more often in images.

But I bet we will start seeing more of them in the future . .