Starship Asterisk*

M83 Star Streams

Explanation: Big, bright, and beautiful, spiral galaxy M83 lies a mere twelve million light-years away, near the southeastern tip of the very long constellation Hydra. This deep view of the gorgeous island universe includes observations from Hubble, along with ground based data from the European Southern Observatory's very large telescope units, National Astronomical Observatory of Japan's Subaru telescope, and Australian Astronomical Observatory photographic data by D. Malin. About 40,000 light-years across, M83 is popularly known as the Southern Pinwheel for its pronounced spiral arms. But the wealth of reddish star forming regions found near the edges of the arms' thick dust lanes, also suggest another popular moniker for M83, the Thousand-Ruby Galaxy. Arcing near the top of the novel cosmic portrait lies M83's northern stellar tidal stream, debris from the gravitational disruption of a smaller, merging satellite galaxy. The faint, elusive star stream was found in the mid 1990s by enhancing photographic plates.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

APOD Robot wrote:spiral galaxy M83 lies a mere twelve million light-years away

Just for an interesting comparison, twelve million years ago, human predecessors were not yet even a twinkle in the eye of the great apes. But that is only slightly more boggling to me than the fact that this APOD was composed from five separate data sources. I feel like such a great ape.

M83 was the only galaxy discovered by the Frenchman Nicolas Lacaille using a 0.5 inch refractor at Cape Town in 1751. I suggest we call it Lacaille's galaxy.

That's a fascinating and beautiful image. I have to wonder about the very red color of the dwarf galaxy, however. Certainly the dwarf lacks star formation, although I find it slightly fascinating that a galaxy without star formation is so grainy in texture. Presumably we are seeing red giants, although I think they are surprisingly well resolved in view of how far away the galaxy is. The smooth population of the dwarf galaxy also seems redder than the smooth old population of M83, which is very unusual. Normally, dwarf galaxies are more metal-poor and therefore less red than large galaxies.

It could be that the dwarf galaxy has been photographed and processed in a different way than the portrait of "M83 proper", so that the color of the two galaxies (or the large galaxy and the star stream) are not quite comparable.

In any case, this is a very fascinating confirmation of the fact that shredded dwarf galaxies and their star streams roam the outskirts of many, probably most, major galaxies.

Ann

Ann wrote:That's a fascinating and beautiful image. I have to wonder about the very red color of the dwarf galaxy, however. Certainly the dwarf lacks star formation, although I find it slightly fascinating that a galaxy without star formation is so grainy in texture. Presumably we are seeing red giants, although I think they are surprisingly well resolved in view of how far away the galaxy is. The smooth population of the dwarf galaxy also seems redder than the smooth old population of M83, which is very unusual. Normally, dwarf galaxies are more metal-poor and therefore less red than large galaxies.

It could be that the dwarf galaxy has been photographed and processed in a different way than the portrait of "M83 proper", so that the color of the two galaxies (or the large galaxy and the star stream) are not quite comparable.

In any case, this is a very fascinating confirmation of the fact that shredded dwarf galaxies and their star streams roam the outskirts of many, probably most, major galaxies.

Ann

I don't really know, but it seems a little dubious to deduce facts about a smaller, satellite galaxy, now merged with M83, from the stellar tidal stream left behind from the merger. Could the stream just as easily be a combination of both original galaxies?

Edit: Or maybe we see in the tidal stream, the remnants of a globular cluster (sometimes classified as a satellite galaxy) which was full of old stars, but is now mainly consumed by M83? In which case, I don't really know if the remnant stream would be a mixture, or not.

I spotted something in todays APOD what resembles a bow shock. Visually located in M83's star stream, it is probably some 12 million light years closer and located in our own galaxy as it appears to surround a star which would be one of our 'own', judging by its visual size. I've tried to enhance it. Click on the thumbnail for a full size version.



What is it? And if it is a bow shock, what is the source of the energy causing it? I am not an astronomer, but merely an enthusiastic fan of APOD who thinks he has seen something new

The faint, elusive star stream was found in the mid 1990s...

Starstream, yes, but also, I think, a coincidental alignment with a galaxy cluster well behind the starstream in the far distance. How else to explain the large number of elongated "stars" within the starstream? If you download the large image and zoom in on that orangish starstream you can see galaxy shapes all over it, hundreds of them.

Rob

M. Schoenmaker wrote:I spotted something in todays APOD what resembles a bow shock. Visually located in M83's star stream, it is probably some 12 million light years closer and located in our own galaxy as it appears to surround a star which would be one of our 'own', judging by its visual size. I've tried to enhance it. Click on the thumbnail for a full size version.



What is it? And if it is a bow shock, what is the source of the energy causing it? I am not an astronomer, but merely an enthusiastic fan of APOD who thinks he has seen something new

This isn't a bowshock, this is a tidal tail associated with a distant background galaxy.

@Ann: the tidal stream isn't a dwarf galaxy, it would have been completely absorbed by M83.

David Malin is one of the very few people in the world that the word 'legend' is applicable to! He compiled an amazing archive of deep galaxy images, it can be seen here: http://www.aao.gov.au/images/general/HC ... _list.html

The northern tidal tail seems positively chock full of galaxy shaped objects. Some appear edge on, some face on in appearance. These objects seem to be in much greater proportion here than in the surrounding space. Is this attributed to a different data set in this area? What are we looking at here?

Nitpicker wrote:I feel like such a great ape.

Sure you did not mean?

M83-The "Dislocated Arm Galaxy"

FloridaMike wrote:

Nitpicker wrote:I feel like such a great ape.

Sure you did not mean?

Gosh, I haven't seen Grape Ape in several decades. Not worth psychoanalysis, but one of the few vivid memories I have of my early childhood is watching Grape Ape on Saturday mornings. Thanks Beegly Beegly.

I have taken a look at the enlarged picture, which is something I should have done before I made my first post, of course!

It is obvious that the star stream has been imaged in just one filter or color. Either the original filter was a red (or possibly an infrared) one, or else it wasn't necessarily red but has been mapped that way. That is the reason why the star stream looks so red! Unlike M83 itself, the star stream hasn't been imaged in RGB.

There is indeed a profusion of galaxies that can be seen in or right next to the star stream. But clearly we see all these galaxies just because the resolution is so good. The depth of its resolution makes the portrait of the star stream look almost like a Hubble image. The major galaxy in the picture, M83, has not been imaged to nearly such depth. The deep resolution ends quite abruptly in places, leaving the space above it look devoid or either stars or galaxies.

It is abundantly clear that the stream or tidal tail is made up of stars, and that the small-looking galaxies are background objects.

The lesson that can be learnt from this image is that you have to use one kind of photographic technique to image a bright object, and another technique to image something that is very faint.

Ann

A little explaining about the image. Because it was assembled from a variety of different data sources there are unavoidable differences in resolution and depth among the various parts of the image. The star stream itself was imaged under superb conditions (three filters, BVR) with the VLT (VIMOS) and was very aggressively processed to bring out the resolved stars. This probably explains why so many distant background galaxies are also seen through the star stream as considerable stretching was applied to amplify the extremely weak signal of the stream. The stars within the stream were barely apparent in the unstretched data. Also as some may have noticed I ran out of VLT data along the left side of the resolved stream . Although the stream was imaged in BVR the resolved stars were only apparant in the "R" band. Regarding the color....I'm not sure these stars are red giants in the classic sense but my knowledge is limited here. Dr. David Martinez-Delgado explains the phenomenon in one of his papers which you can download at the link below.
www.robgendlerastropics.com/Starstreams.pdf

Thanks, Rob, that explains why some of the superimposed foreground stars are non-red!

I'd say that practically all of the resolved stars in the stellar stream must be red giants. In a galaxy, cluster or star stream where you have no young blue stars, the red giants are the brightest stars.

Ann

Amazing image and composite from so many sources...quite the project, no doubt.

What I find interesting....is the dust lane THROUGH the central hub...or over it....as it is hard to tell in a two dimensional, face on, image...there is a circle there...and it is off center from the central hub...it looks displaced by some means....looked out of place to me.

With so much star formation...M83 is also classified as a Starburst Galaxy...there is also a second nucleus reported by some people...there is a wide shot of the area that shows the splattered, and splayed layout of the arms...it must have got CREAMED in the merger...only the central area stayed relatively intact...I suspect it is so for many other mergers..but due to photography, not all details are shown.

http://astronomy.activeboard.com/t2987694/m83/?page=2

Great Job...interesting object...

:---[===] *

Looking elsewhere around the image of M83, notice the two larger background galaxies on the left-side approximately behind the Outer Main Spiral Arm. The more orange'ish of the two has a faint ring around it. That ring doesn't look to be part of the structure of the background galaxy, as the orientation is nearly perpendicular to the somewhat oblique face-on barred spiral structure. Could it be a form of Gravitational Lensing ?? Or some form of faint illumination of the M83 galactic dust cloud by that background galaxy - as the coloration is a good match for that of the foreground M83 dusty outer disk ?? Or a simple artifact of the image processing - sharpening or deconvolution ??