Tidal streams in the Southern Pinwheel

[marco (Marco Lorenzi)]

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

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 . 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.

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

Here is the link:
http://www.glitteringlights.com/Imag...4_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..

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

I hope you will like it

Clear Skies
Marco

[Octane (Humayun)]

That is just so stunningly beautiful.

Another masterpiece.

Awesome work, my friend.

H

[TrevorW]

Very nice indeed, well done

[strongmanmike (Michael)]

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 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

Mike

[marco (Marco Lorenzi)]

Originally Posted by Octane

That is just so stunningly beautiful.

Another masterpiece.

Awesome work, my friend.

H

Thanks H

Originally Posted by TrevorW

Very nice indeed, well done

Thanks Trevor

Clear Skies
Marco

[marco (Marco Lorenzi)]

Originally Posted by strongmanmike

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

Mike

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 ) 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 .

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 *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 ).

Thanks for pointing this out

Clear Skies
Marco

[strongmanmike (Michael)]

Originally Posted by marco

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 *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 ).

Thanks for pointing this out

Clear Skies
Marco

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 ...here in lies the problem of feature specific enhancement.

As I said, still a very cool image

Mike

[strongmanmike (Michael)]

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 (Mike)]

Stunning image Marco, magnificent!

[jjjnettie (Jeanette)]

Spectacular!

[Stevec35 (Steve)]

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

Cheers

Steve

[multiweb (Marc)]

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.

[Peter Ward]

Originally Posted by 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.

Ditto.

[marco (Marco Lorenzi)]

Originally Posted by 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

Originally Posted by 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.

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

Originally Posted by iceman

Stunning image Marco, magnificent!

Thanks Mike

Originally Posted by jjjnettie

Spectacular!

Thanks JJJinette

Originally Posted by Stevec35

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

Cheers

Steve

Thanks Steve

Originally Posted by 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.

Thanks Marc

Originally Posted by Peter Ward

Ditto.

Thanks Peter

Clear Skies
Marco

[strongmanmike (Michael)]

Originally Posted by marco

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

Marco

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/strongmanmike20...36997/original

2) http://www.pbase.com/strongmanmike20...36998/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 (Mariusz)]

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.

Originally Posted by 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/strongmanmike20...36997/original

2) http://www.pbase.com/strongmanmike20...36998/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

[RobF (Rob)]

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