Starship Asterisk*

NGC 5965 and NGC 5963 in Draco

Explanation: These two spiral galaxies make a photogenic pair, found within the boundaries of the northern constellation Draco. Contrasting in color and orientation, NGC 5965 is nearly edge-on to our line of sight and dominated by yellow hues, while bluish NGC 5963 is closer to face-on. Of course, even in this well-framed cosmic snapshot the scene is invaded by other galaxies, including small elliptical NGC 5969 at the lower left. Brighter, spiky stars in our own Milky Way are scattered through the foreground. Though they seem to be close and of similar size, galaxies NGC 5965 and NGC 5963 are far apart and unrelated, by chance appearing close on the sky. NGC 5965 is about 150 million light-years distant and over 200,000 light-years across. Much smaller, NGC 5963 is a mere 40 million light-years away and so is not associated with the edge-on spiral. Difficult to follow, NGC 5963's extraordinarily faint blue spiral arms mark it as a low surface brightness galaxy.

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That's a lovely picture! Congratulations, Stephen Leshin!

Ann

Assuming the two galaxies NGCs 5963 & 5963 are approximately the same size in the image that would make the diam. of 5963 about 50,000 lt. years . The reference paper by S´anchez-Salcedo suggesting that a model of this Low surface brightness galaxy has a gas density which results in not so bright stars is interesting.

It raises the question to me as to how such an inactive galaxy can be a spiral? Yet there it is, as plain as the nose on your face.

Nicely done Stephen!

bactame wrote:Assuming the two galaxies NGCs 5963 & 5963 are approximately the same size in the image that would make the diam. of 5963 about 50,000 lt. years . The reference paper by S´anchez-Salcedo suggesting that a model of this Low surface brightness galaxy has a gas density which results in not so bright stars is interesting.

It raises the question to me as to how such an inactive galaxy can be a spiral? Yet there it is, as plain as the nose on your face.

It is, of course, possible that the stars of the arms of NGC 5963 are not so bright, but I do want to point out that the arms are blue. In other words, the arms are dominated by blue stars. A stellar population that is dominated by blue light must contain a good number of stars that are both young and at least relatively bright.
NGC 5963 is not the only spiral that has a set of faint arms. Now-defunct telescope GALEX, whose mission was to image the sky in ultraviolet light, detected a set of faint ultraviolet (and therefore also blue) arms around small spiral galaxy NGC 4625. Somewhat larger spiral NGC 4618, at bottom right, was not found to have any faint outer arms.




Ann

It is interesting to consider today's galaxies, NGC 5965 and NGC 5963.

The edge-on yellow galaxy, NGC 5965, is well-formed, although its disk is slightly "undulating". This is probably more the rule than the exception for disk galaxies, at least for spiral galaxies. Note that NGC 5965 is almost certainly interacting with the small yellow galaxy to the right of it.

NGC 5965 has an extensive yellow bulge. It has a very obvious dust lane and several sets of dust rings(?) in its disk. Its outer edges are blue. Both the color gradient and the general shape of NGC 5965 reminds me of the Andromeda Galaxy, although NGC 5965 is clearly bigger.

It is interesting to compare the blue magnitude of NGC 5965 with the far infrared magnitude of this galaxy. Two things may be noted here. Galaxies which are seen edge-on are often a little extra bright in far infrared light. That is because they present their dustiest aspect to us, and far infrared light typically traces warm dust. Since NGC 5965 is seen almost edge on, flaunting its dust lane at us, it ought to be fairly bright in far infrared light just because of that.

The other thing to remember about far infrared light is that it typically traces star formation, too. Star formation warms the dust and makes it emit a lot of far infrared light.

Spiral galaxies that are "middle of the road", neither rich nor poor in dust and star formation, are typically about equally bright in blue light and in far infrared light. So what about NGC 5965?

Fascinatingly, edge-on NGC 5965 with its prominent dust lane is comparatively faint in far infrared light. It is about 0.8 magnitudes fainter in far infrared light than in blue light. There can't be a lot of star formation going on in that galaxy.

What about NGC 5963? It is seen almost face on, and there is very little visible dust in it. Yet this blue galaxy is about 0.8 magnitudes brighter in far infrared light than in blue light!

There is a reason why NGC 5963 is blue. It may be faint, but it is dominated by young stars. And there is a good deal of star formation going on inside it.

Ann

Ann seems to think i am talking about blue stars, not so. NGC5963 is a low luminosity GALAXY. There other things that are blue besides stars. These types of galaxies have low densities of gas and thus form stars slowly. Are classes of blue stars in this galaxy? I have no idea, it the galaxy that is low luminosity. Even in this image that is obvious but i don't say this because of the image. The last two links in the blurb for this apod supply my opinion.

Beautiful and beautifully ironic that an object without an edge can be viewed edge-on.

bactame wrote:Ann seems to think i am talking about blue stars, not so. NGC5963 is a low luminosity GALAXY. There other things that are blue besides stars. These types of galaxies have low densities of gas and thus form stars slowly. Are classes of blue stars in this galaxy? I have no idea, it the galaxy that is low luminosity. Even in this image that is obvious but i don't say this because of the image. The last two links in the blurb for this apod supply my opinion.

There's not much in a galaxy that can be blue except for stars.

I don't understand the relevance of the Sánchez-Salcedo paper to this discussion. It doesn't deal with the nature of low surface brightness galaxies, but with using them as tools for exploring how dark matter interacts with itself. It seems primarily concerned with the density profile of the dark matter halo of this galaxy, not the overall density of ordinary matter.

Beautiful picture. Blue galaxy ngc5963 definitely deserves in depth observation. Recommend warm red wine served with cinnamon as an operating aid.
And, the discussion for ngc4625 and ngc4618 is well received.

Chris Peterson wrote: There's not much in a galaxy that can be blue except for stars.

What about a particularly dense cluster of low luminosity boo berries?

Never ceases to astonish me how something so enormous and distant can appear so beautifully elegant from our viewpoint. They seem like small but perfectly formed islands; galaxies are wondrous things. Seen from somewhere over there, our own must appear equally captivating. Great image!

This is a fantastic image. One if the best pictures of galaxies I've ever seen. It just appeals to me in some way. Simply amazing.

One more thing should be said about why the arms of NGC 5963 are both blue and faint. There is only one possible explanation, in my opinion. There has been recent star formation in the arms of NGC 5963, and star formation may very well still be going on in the arms. But there hasn't been much star formation there before.

A substantial population of intermediate or even old stars would have made the arms so much brighter. That, however, would have required a substantial amount of star formation that got started, say, at least a billion years ago. It is not inconceivable that star formation got started in the arms of NGC 5963 a billion years ago or even earlier, but if so, there can only have been very small amounts of it.

The main reason for the blue color of the arms of NGC 5963 is that the light of the arms is dominated by young blue and relatively bright stars. The reason why the arms are still so faint is that there just aren't very many stars in them, and certainly not very many intermediate or old stars.

Ann