APOD: The Hydra Cluster of Galaxies (2012 May 12)

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APOD: The Hydra Cluster of Galaxies (2012 May 12)

Post by APOD Robot » Sat May 12, 2012 4:06 am

Image The Hydra Cluster of Galaxies

Explanation: Two stars within our own Milky Way galaxy anchor the foreground of this cosmic snapshot. Beyond them lie the galaxies of the Hydra Cluster. In fact, while the spiky foreground stars are hundreds of light-years distant, the Hydra Cluster galaxies are over 100 million light-years away. Three large galaxies near the cluster center, two yellow ellipticals (NGC 3311, NGC 3309) and one prominent blue spiral (NGC 3312), are the dominant galaxies, each about 150,000 light-years in diameter. An intriguing overlapping galaxy pair cataloged as NGC 3314 is just above and left of NGC 3312. Also known as Abell 1060, the Hydra galaxy cluster is one of three large galaxy clusters within 200 million light-years of the Milky Way. In the nearby universe, galaxies are gravitationally bound into clusters which themselves are loosely bound into superclusters that in turn are seen to align over even larger scales. At a distance of 100 million light-years this picture would be about 1.3 million light-years across.

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Ann
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Re: APOD: The Hydra Cluster of Galaxies (2012 May 12)

Post by Ann » Sat May 12, 2012 6:28 am

Interesting.

As a color freak, I must extract as much information as I possibly can from the color of the picture. The first thing I noticed was that the overall color of the "blue" spiral galaxy (NGC 3312) seems to be extremely similar to the overall color of the "yellow" elliptical galaxies (NGC 3311 and 3309). The yellow bulge of NGC 3312 seems to be an almost deeper yellow color than the central parts of the elliptical galaxies, and the huge extended halos of the ellipticals appear to be grayish in color. The disk of NGC 3312 is not very blue in this picture, but more grayish, too. Fascinatingly, my software confirms that the large spiral and the two largest ellipticals have almost identical B-V indexes, although the spiral galaxy is bluer (but not very blue) in U-B.

What does that mean? Well, a reason for the rather non-blue B-V index of NGC 3312 is probably that we see it highly inclined, so that a lot of the dust of NGC 3312 is in our line of sight, reddening the galaxy. The very yellow color of the bulge of NGC 3312, compared with the paler yellow color of the centers of the two large ellipticals, could also be due to more dust even in the bulge of NGC 3312 than in the centers of the ellipticals.

But what about the almost identical gray color of the disk of NGC 3312 and the halos of the ellipticals? It is fascinating to think that stellar populations of the disk of the spiral and the halos of the ellipticals are not so different. However, I think we are looking at different phenomena. The disk of NGC 3312 is probably strongly dominated by an intermediate population, with large numbers of F- and G-type stars, similar to Procyon and, indeed, the Sun. The halos of the ellipticals, on the other hand, might contain a considerable number of very old metal-poor stars, which spend part of their lives as bright blue horizontal branch stars.

My impression of NGC 3312 is that it is not very blue and not very active in star formation. It definitely contains a number of young stars, but not necessarily that many. In spite of its inclined position its far infrared magnitude is fainter than its blue magnitude, which suggests that it is running out of fresh gas and dust. And its not impressively blue U-B value suggests that there aren't that many hot ultraviolet stars in there.

The fascinating overlapping galaxy pair, NGC 3314, looks bluer to me than either NGC 3312 or the large ellipticals. The apparent blue color of NGC 3314 is probably due to the fact that the smaller foreground spiral galaxy has a small and not very bright yellow bulge, and it blocks the probably larger and brighter yellow bulge of the background galaxy from our view.

It is very interesting to compare the color of the foreground Milky Way stars with the color of the background galaxies. The fainter of the prominent foreground stars is a late K-type star, and the brightest of the foreground stars is an even redder M-type star. If the bulges of the galaxies had been crammed full of stars similar to the two bright Milky Way stars in this picture, then the bulges of the galaxies would have been very deeply orange in color. Bear in mind that the galaxies are far away and redshifted due to the expansion of the universe, and they are also sitting behind millions of light-years of dust, which must also redden the color of them. Therefore they must look considerably yellower than if they had been nearby. Yet the bulges and the centers of the galaxies are paler, less yellow, than the foreground M-type star. Therefore the light output of the galaxies is dominated by stars less red than the two Milky Way foreground stars.

Note, in the picture, a line of Milky Way stars that seem to rise from the left side of the large spiral galaxy, NGC 3312. First there is a blue star, then there is a small orange star and then there is a larger orange star. Then there is a galaxy, and then there is something that looks like a blue coffee bean! Either it is a very strange thing in the Milky Way, possibly a planetary nebula, or else it is two interacting and starforming galaxies.

Finally, remember that NGC 3314 consists of two overlapping galaxies, one at 117 million light-years and one at 140 million light-years away. I wonder if NGC 3312, the large spiral galaxy, is not also a foreground object around 117 million light-years away or so, while the ellipticals may be around 140 million light-years away. My software agrees that that may be the case.

Ann
Last edited by Ann on Sat May 12, 2012 5:14 pm, edited 1 time in total.
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sage

Re: APOD: The Hydra Cluster of Galaxies (2012 May 12)

Post by sage » Sat May 12, 2012 1:08 pm

Incredible. Thanks Angus and apod.

I see the coffee bean! :D Galactic Latte Grande, please.

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Re: APOD: The Hydra Cluster of Galaxies (2012 May 12)

Post by bystander » Sat May 12, 2012 1:34 pm

sage wrote:I see the coffee bean! :D Galactic Latte Grande, please.
How about some cosmic latte?
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
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Re: APOD: The Hydra Cluster of Galaxies (2012 May 12)

Post by biddie67 » Sat May 12, 2012 1:55 pm

I'm always blown away by the fragile and difficult sense of the size of the Universe ~~ it's makes my little acre (which I dearly love wandering about on) absolutely pale in comparison.

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Re: APOD: The Hydra Cluster of Galaxies (2012 May 12)

Post by ritwik » Sat May 12, 2012 4:10 pm

Click to play embedded YouTube video.

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Re: APOD: The Hydra Cluster of Galaxies (2012 May 12)

Post by Mactavish » Sun May 13, 2012 3:14 am

Does anyone know where we can find a good detailed image of NGC 3312? I’ve searched about a hundred websites with no luck. Thanks.

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Re: APOD: The Hydra Cluster of Galaxies (2012 May 12)

Post by bystander » Sun May 13, 2012 4:45 am

Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

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Ann
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Re: APOD: The Hydra Cluster of Galaxies (2012 May 12)

Post by Ann » Sun May 13, 2012 5:17 am

Mactavish wrote:Does anyone know where we can find a good detailed image of NGC 3312? I’ve searched about a hundred websites with no luck. Thanks.
I have to agree with you that there appears to be no really good pictures of this galaxy.

This is the best picture I could find. What I like about it is that it gives us a chance to assess the amount of star formation in NGC 3312 and the number of bright young clusters. Judging from the picture, there appears to be exactly four clusters of bright young stars in NGC 3312! Three of these clusters can be seen to the upper right of the bulge of NGC 3312, and one can be seen to the left of the bulge. These clusters stand out because of their blue color. There is also a completely non-blue whitish knot above the bulge, but because of its color I doubt that it is a cluster - unless it is a super-bright globular cluster, of course! Another bright, isolated, white and possibly also bluish knot is seen just below the bulge, almost "touching" it. The two last knots are located in otherwise very "quiet" and not particularly dusty parts of the galaxy, which is another reason for me to doubt that they are clusters.

There is an obvious blue-green foreground star seen to the lower left of the bulge of NGC 3312. Just to the left of that foreground star, the disk of NGC 3312 looks bluish. There is clearly a young population here, but no bright clusters.

NGC 3312 reminds me somewhat of the Messier galaxy M90. As you can see, M90 has a yellow bulge and a "grayish" disk devoid of star formation and bright clusters (more so than NGC 3312). There is admittedly star formation in the inner disk of M90, right next to the yellow bulge.

The disk of M90 looks almost perfectly "undisturbed", in marked contrast to the disk of NGC 3312. The disk of NGC 3312 shows very large-scale "disturbances". When you look at the picture of it, there appears to be a long, dusty, inverted "S"-shaped arm superimposed on the disk to the left of the bulge. This structure shows some star formation. To the right of the bulge, there is a long, diffuse, straight, seemingly dustless structure almost superimposed on the bulge. Above the bulge, there disk forms a huge, V-shaped "portal"-like structure. There appears to be a small amount of star formation on the left side of this "portal".

What a strange galaxy!

Ann
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