Starship Asterisk*

Shell Galaxy NGC 7600

Explanation: Similar in size to the Milky Way, elliptical galaxy NGC 7600 is about 150 million light-years distant. In this deep image, spanning about 1/2 degree on the sky toward the constellation Aquarius, NGC 7600 sports a remarkable outer halo of nested shells and broad circumgalactic structures. The tantalizing features can be explained by the accretion of dark matter and stars on a cosmic timescale. In fact, a movie generated by simulating galaxy formation using a cosmological model with cold dark matter for the halos of merging galaxies reproduces the appearance of NGC 7600 in amazing detail. The remarkable simulation movie is available here on Vimeo and here in other formats. It presents compelling evidence that detailed features of galaxy mergers observed with small, wide field telescopes on planet Earth, are natural consequences of galaxy formation and fundamental properties of dark matter.

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There must be a typo on the distnace. Perhaps they can change it.

Jeff Baldwin wrote:There must be a typo on the distnace. Perhaps they can change it.

Right. It should be 50 Mpc, or 160 million light-years.

Jeff Baldwin wrote:There must be a typo on the distnace. Perhaps they can change it.

Indeed. If it were the size of the Milky Way (say ~100,000 Light years) and is 150,000 light years away, it would dominate our skies!

I've sent off an email to the editor about the distance.

The two galaxies probably would have collided by now!

But don't forget - there's a typo in your message, too: distnace should be distance.

In addition to the distance problem the concluding sentence: It presents compelling evidence that detailed features of galaxy mergers observed with small, wide field telescopes on planet Earth, are natural consequences of galaxy formation and fundamental properties of dark matter.
It refers to the movies and the sentence is saying small telescopes are produced by dark matter? If so let me have a Celestron as un-small as available and thank you Mr Dark matter.

owlice wrote:I've sent off an email to the editor about the distance.

I also sent Jerry a note, he will get it corrected.

Regards,

Ken Crawford
http://www.imagingdeepsky.com

From what I observed on the video, there is an alternative explanation.

As a nucleus of one larger galaxy come in, about 1:04 into the video. It reminded me of a "Newton's Cradle". As the gravity of the central object is centered, the other galaxy "goes through it". Well, the momentum and inertia is greater, so it goes out farther in the beginning, and the stars get "splayed" out in a "fan-like" formation. When it comes back in, going the other way, the momentum and inertia is less, and as it goes through, gets splayed in the other direction and fans out, again and again and again, etc... THUS, you get a fanned out, "shell" effect, from the FREQUENCY of the swinging in and out of the galactic center as it is "cannibalized". The individual Stars would continue on with their momentum and inertia. As more and more nuclei are coming in, there is more and more effect. The over all impression of this, is "WAVES" of off-streaming stars. The reason why the wave pattern persists is that, as more and more stars are added to the pool, there is more mass in the outer regions and that would tend to slow down the speed and hold them out there in that pattern. So the waves do not collapse back into the center of the newly forming, larger galaxy. The mass, being distributed all round, would tend to preserve the pattern, even though Stars are continually moving back into and through the center of the forming galaxy, and they keep going out from center again, they only go as far as their momentum and inertia will allow them. As they are influenced by the warped space of other stars out there, they form a pattern. I am reminded of one of those, "tsh, tsh, tsh, Lawn sprinklers, that go around in a swath and then, "tshhhhh", back to the starting point, throwing water drops out in an arc.
So, the wave pattern we see, is from the slowing and stopping point of the momentum of the stars. There are so many doing this at the same time, it looks like a wave. But I see many waves, smaller, and smaller, and that is because with each successive pass, the momentum and speed is less and less. But there are so many, that their masses tend to hold there for a while. You can see in places where this "breaks down" and the pattern falls away.

I am sorry, but I don't see Dark Matter as influencing this. Or, not influencing it much....WHY?

Because the Dark Matter of two Galaxies in collision KEEP GOING AND PASS THROUGH ONE ANOTHER, The DM fields do not stop... even though the two galaxies have slowed, and basically have stopped. (There have been APOD pictures of the day, that illustrate this.) The DM doesn't have much, if any, affect on things. And this video shows a more "COMPACT" effect of influence. It is like two trucks carrying potatoes colliding. The two trucks smash into each other, and basically stop, but the potatoes fly on out of the trucks and keep going, and really have no influence on the crash, or what the crash looks like, or where parts of the trucks land, or in what pattern. That would be dependent on the individual parts, their masses, momentum's, and inertia, and what they HIT, and the dissipation of that force, and angle of deflection, etc... The intrinsic mass just isn't there for the potatoes to affect all that. So, while Dark Matter may have a subtle infra-structural effect behind the scenes on the clumping of matter, (and the structure of the Universe suggests this at least), it does not have the density to affect the close up movement of matter, nor what particular "pattern" such things might take.
In other words, it is all bound up in the VISIBLE MATTER, its masses, and momentum's, and inertia's, and their influences on each other. When smaller nuclei come in and go around the larger main center, they influence, and even "TAKE", stars with them. (So cool.) They leave the main center, and take stars that are further away from center, not as much influence from center, with them. That is not DM. That is not "determined" by Dm. My observation/opinion, such as it is....

It is like the end of the movie, "The Quick and the Dead". The girl shoots the bad guy in the eye, and he does a back flip. A bullet, even at that speed, does not have the mass to do that. The bullet would go through his head, and he would drop. It does not have the MASS, to lift him up off his feet into a back flip. (NICE EFFECT THOUGH). Movie Myth....Myth BUSTED!
You may not agree. That is OK.

:---[===] *

I was mystified by the color of the image. Many of the faint features, including nearly all of galaxy NGC 7600 itself, appeared to be in black and white, while some brightish foreground stars were boldly colored. I checked NGC 7600 with my software, and it had the typical colors of an elliptical galaxy and should therefore appear yellow.

The explanation is to be found on Ken Crawford's homepage. These were the filters and exposure times used to make the image:

Filter Exposures
Clear/ Lum 680 minutes
Red 160 minutes
Green 160 minutes
Blue 140 minutes

So the the unfiltered exposure, which must produce gray images, was longer than the exposures through all the other filters put together. Therefore faint objects basically look gray in this image, while bright point sources look colored. Ken Crawford wrote on his homepage:

This deep image shows faint features not previously seen in color.

So this is basically a combined color and black and white image, whose purpose was to bring out features so faint that it hasn't been possible to detect them in purely "color-filtered" images.

I was glad to read about David Malin's contribution in detecting these shell galaxies. He was the first person to discover these shells, as he described in his book. A View of the Universe from 1993. With the help of David Carter, he was able to explain these shells as features caused by collisions. But by the time Malin and Carter's paper was published, in 1980, I don't think dark matter was thought of as a major contributor to the creation of these shells.

Ann

Ann wrote:I was mystified by the color of the image. many of the faint features, including nearly all of galaxy NGC 7600 itself, appeared to be in black and white, while some brightish foreground stars were boldly colored. I checked NGC 7600 with my software, and it had the typical colors of an elliptical galaxy and should therefore appear yellow.

The explanation is to be found on Ken Crawford's homepage. These were the filters and exposure times used to make the image:

Filter Exposures
Clear/ Lum 680 minutes
Red 160 minutes
Green 160 minutes
Blue 140 minutes

So the the unfiltered exposure, which must produce gray images, was longer than the exposures through all the other filters put together. Therefore faint objects basically look gray in this image, while bright point sources look colored.

It doesn't matter how long the luminance data is compared with the color, that doesn't change the final color or color saturation.

Our eyes are much more sensitive to detail in luminance than chrominance. This is apparent in cheaply printed images (especially comics), where the colors are sloppy and don't stay inside the lines. But it doesn't matter- our eyes see the black outlines, and overlook the inaccurate color. With an LRGB image, a lot of time is devoted to luminance in order to get a high signal-to-noise image, and then less time is devoted to color, because we are relatively insensitive to color noise.

Of course, if the object is sufficiently faint, there may be essentially zero signal in the color channels. But I don't think that's the case here- NGC 7600 isn't particularly faint. Other images, made using different techniques, also show very little color in NGC 7600. I think it is intrinsically weakly colored.

The simulation is amazing!

Just to be clear on the method used on this image, it is an LRGB. But, notice that all the color data was taken unbinned. Many of us on the Star Stream Team do this because many of the streams we try to detect are very faint. In fact, the Professionals we work with from Max Planck have measured my data down to about 29 mags/sq arc/sec. You are correct in with an LRGB method you are "tinting" the grey scale image with color. But, If you take all of your color data unbinned you can then sum it together along with the "Clear" data which does increase signal to noise and increases contrast. This produces a type of synthetic luminance. I not use a synthetic luminance step on this image however.

To get as close as we can on a "white point" color balance we do characterize our systems with a G2V measurement to get the R-G-B combine ratios. But, these images are taken over several nights and no extinction of color was taken into account. So during the color combine process there is always "tweaking" of the color balance. Of course, the data used for the AJ paper was strictly the luminance data taken throw a clear filter (not IR Blocked) to get every photon possible. The color data is then added for this presentation but the stretching methods to show the faint stuff along with the bright stuff can change the color balance a bit. So it is not a “perfect” color but in this image it was deep enough to bring some of the color of the galaxy out.


Ken Crawford
http://www.imagingdeepsky.com
http://www.aicccd.com

Ann wrote:II was glad to read about David Malin's contribution in detecting these shell galaxies. He was the first person to discover these shells, as he described in his book. A View of the Universe from 1993. With the help of David Carter, he was able to explain these shells as features caused by collisions. But by the time Malin and Carter's paper was published, in 1980, I don't think dark matter was thought of as a major contributor to the creation of these shells.

Ann

Thanks for noticing that Ann. The AJ paper also pointed to David Malin's (and Carter's) work on shell galaxy structures. I also had the privilege of having dinner last summer with David Malin when I presented at AAIC. He told me about the methods he (and Carter) used to bring out the shells in those days. Very interesting evening! I have to admit that our “digital” dark rooms are much easier to work in

Sorry about the number of posts, but I did not want to do this in one large reply.

For those interested in the "accepted" processing methods that the Star Stream Team uses for stream - shell type detections, here is a link to a paper that includes what our amateur team leader R. Jay Gabany developed for processing the faint star streams. Because the methods are a bit different they had to be well described for the professional community.

See page 5 (2.2) for the discription of some of the processing methods we use. http://www.cosmotography.com/images/ngc5907_def.pdf

What is exciting to me about NGC7600 is this is a Pro-am collaboration with a great team of professionals. My work on NGC7600 is a contribution to science as well as a "pretty" picture and represents my 2nd time in a AJ paper. I believe we are in the golden age of Pro-am collaborations as large telescope time is hard to get and expensive. Most of the institutional resources are going to larger instruments and smaller, older systems are starting to drop off the map needing repairs.

Amateurs have a advantage over professionals as we own our own equipment and we can sit on a target as many nights as we want to. So when lower resolution, wilder field but deep data can work this is where amateurs can step in.

Have a great holiday weekend!

Ken Crawford
http://www.imagingdeepsky.com
http://www.aicccd.com

NGC 7600 and the dark matter is a important topic.
The dark matter is present in the Universe. Matter whitout light, but whit very much
gravity power.

This galaxy reminds me of the rectangle nebula.

LRGB split to here