APOD: Edge on NGC 3628 (2011 Nov 04)

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APOD: Edge on NGC 3628 (2011 Nov 04)

Post by APOD Robot » Fri Nov 04, 2011 4:11 am

Image Edge on NGC 3628

Explanation: Sharp telescopic views of magnificent edge-on spiral galaxy NGC 3628 show a puffy galactic disk divided by dark dust lanes. The tantalizing scene puts many astronomers in mind of its popular moniker, The Hamburger Galaxy. About 100,000 light-years across and 35 million light-years away in the constellation Leo, NGC 3628 shares its neighborhood in the local Universe with two other large spirals, a grouping otherwise known as the Leo Triplet. Gravitational interactions with its cosmic neighbors are likely responsible for the extended flare and warp of this spiral's disk, populated by the galaxy's young blue star clusters and tell tale pinkish star forming regions. Also a result of past close encounters, a faint tidal tail of material is just visible extending upward and left in this deep galaxy portrait.

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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by Beyond » Fri Nov 04, 2011 4:37 am

Clicking the in mind link reminds me of "Wimpy"- "I'll gladly pay you tuesday, for a hamburger today". Gomez's Hamburger also reminds me of the commercial - "WHERE's THE BEEF" :?: :?: All i see is two halves of a 'light' bun. Must be a veggi-burger.
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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by bystander » Fri Nov 04, 2011 4:48 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.
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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by Beyond » Fri Nov 04, 2011 4:57 am

MAN!! That one might even feed Paul Bunyan :!: :chomp:
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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by Ann » Fri Nov 04, 2011 9:55 am

This is a very good, deep image of NGC 3628. It is in fact the first image of this galaxy where I have seen pink emission nebulae. I believe, therefore, that although emission nebulae are present in NGC 3628, they are relatively faint and few. In other words, I would guess that there isn't all that much star formation going on inside this galaxy. We may note, too, that the "neighbors" of NGC 3628 are also relatively poor in star formation. In this image of M66, you can identify the emission nebulae as spots of green, and the clusters and associations of young stars are seen as localized, distinctly blue knots. You can see that although parts of M66 are rich in star formation, the galaxy has an extended envelope of intermediate, middle aged stars, seemingly devoid of star birth. As for M65, the other neighbor of NGC 3628, it has almost shut down its star formation altogether.

The reason for the relative dearth of star formation may be that these galaxies have been jostling one another for a long time, driving much of their combined gas supply out of one another.

As for today's APOD, I note that the color balance is such that the bright star near the bottom of the image looks blue, even though the color index of this star (TYC 861 10 10) is very similar to the color index of the Sun. In other words, this image brings out very many blue details, which means that we get to see a lot of the young blue stars of this galaxy.

Finally, you've got to check out this APOD, which really shows you the tidal tail of NGC 3628.

Ann
Last edited by Ann on Fri Nov 04, 2011 1:45 pm, edited 1 time in total.
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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by neptunium » Fri Nov 04, 2011 12:12 pm

Well, it doesn't look too tantalizing to me...

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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by orin stepanek » Fri Nov 04, 2011 12:40 pm

It kind of reminds me of a wobbling plate! :wink:
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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by neufer » Fri Nov 04, 2011 1:39 pm

Ann wrote:
Finally, you've got to check out this APOD, which really shows you the tidal tail of NGC 3628.
`Mine is a long and a sad tale!' said the Mouse, turning to Alice, and sighing.

`It IS a long tail, certainly,' said Alice, looking down with wonder at the Mouse's tail; `but why do you call it sad?'
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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by Rouzbeh » Fri Nov 04, 2011 2:09 pm

Wow nce one!
Amazing Detail!

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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by Psnarf » Fri Nov 04, 2011 3:02 pm

I can see the upper-left tidal tail in the enlarged image. Is that small bit of fuzz just below the centre of the galaxy a remnant of the same tidal tail?


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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by drollere » Fri Nov 04, 2011 4:30 pm

i'd say this is actually "the wimpy galaxy" because it seems already to have eaten several hamburger galaxies and hasn't quite digested them all yet. perhaps it's even feeling a little indigestion. (proving the rule, you pay for today what you ate yesterday.)

i don't quite get ann's comment on star formation, since the dust lane is so broad and dense. dust is just as much part of star formation as elemental hydrogen and helium, and the dust lane clearly obscures everything that is going on inside the galactic disk, which is evidently highly disordered. it might be useful to review other galaxy photographs, tilted just enough to show internal structure, where the relationship between circumferential dust and interior star forming regions can be generalized. and mergers may have disrupted the spiral shock waves enough so that the process of sweeping up gas into clouds is temporarily inefficient.

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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by FloridaMike » Fri Nov 04, 2011 7:15 pm

Something about this image gave me a "Galactic Perspective". We think of galaxies as ponderously slow, taking millions of years to complete a revolution. However, from a galaxies perspective it must feel like it is spinning like a top. Thank you APOD.

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Re: APOD: Edge on NGC 3628 (2011 Nov 04)

Post by Ann » Sat Nov 05, 2011 6:05 am

drollere wrote:

i don't quite get ann's comment on star formation, since the dust lane is so broad and dense. dust is just as much part of star formation as elemental hydrogen and helium, and the dust lane clearly obscures everything that is going on inside the galactic disk, which is evidently highly disordered. it might be useful to review other galaxy photographs, tilted just enough to show internal structure, where the relationship between circumferential dust and interior star forming regions can be generalized. and mergers may have disrupted the spiral shock waves enough so that the process of sweeping up gas into clouds is temporarily inefficient.
I think astronomers have a pretty good idea of when star formation can happen and when it can't, but I actually believe that a few mysteries remain for them, too.

So I'm going to post a few more-or-less edge-on galaxies here as links. Some of them show a lot of star formation, while others seem to be completely devoid of if.

Iconic edge-on galaxy M82 has a violent ongoing starburst near its nucleus, but no obvious star formation regions are visible in its disk.

Nearby edge-on galaxy NGC 253 is also undergoing a central starburst. The pink star formation regions in its disk are relatively few and small, but they can definitely be seen in a good RGB image, like this one by R. Jay Gabany.

Some edge-on galaxies with a dust lane appear to be totally devoid of star formation. This RGB Hubble image of the Sombrero Galaxy, M104, shows no sign of either pink emission nebulae or young blue clusters.

Another iconic edge-on galaxy that seems to be incredibly poor in young stars is NGC 3190. However, this Hubble image, processed by Robert Gendler, does show, at highest magnification, small clusters and associations of blue stars. Star-like objects of other colors are also visible, and it is possible that we are seeing individual red supergiants. In the upper right part of the dust lane, we are seeing what just might be a dust-enshrouded region of ongoing star formation. However, it is also possible that we are seeing a young-to-middle-aged bluish cluster which is deeply buried in the dust and therefore strongly reddened. No pink emission nebulae are visible. A possible reason for that may be that the Hubble image is perhaps not an RGB image, but perhaps an IGB (infrared-green-blue) image instead. These filters will not be good at detecting emission nebulae, although the green light of the HB emission should be visible.

You may also want to check out this image of the NGC 3190 Group by Adam Block. At top, you can see elliptical galaxy NGC 3193. NGC 3190 is below it, and NGC 3187 is to the right of NGC 3190. Note the blue color of NGC 3187 and the many pink star formation regions in the dust lane. Near the bottom of the image you can find NGC 3185. This galaxy has a dusty bluish ring surrounding an inner yellow disk or bulge. It is not obvious, however, that there are any pink emission nebulae in the dusty ring.

Edge-on galaxy M98 is not very rich in star formation. However, this rather old image (from January 2004) by Adam Block, taken with equipment that is not top class by today's standards, nevertheless shows an abundance of small pink emission nebulae in the galaxy's disk and in its dust lane.

I couldn't find a good image of M108. This was the best image I found. It is pretty obvious that there are many pink emission nebulae here. Interestingly, the same photographer (Jon K. Olson) has taken an image of the Leo Triplet, of which NGC 3628, the galaxy portrayed in today's APOD, is a member. You can see from this image that no pink spots or young blue clusters are visible. The pink nebulae are definitely there, because today's APOD doesn't lie, but they are very faint.

One edge-on galaxy which hides its star formation regions pretty well is NGC 4565. This image by Bob Franke, which was the APOD of October 15, 2011, is very beautiful. My impression is that the image, like today's APOD, "enhances the blue signal" in order to bring out the younger population in the galaxy's disk. It is very hard to detect any pink emission nebulae in the disk or the dust lane, however.

One of the most perfectly edge-on galaxies that I know of is NGC 891. This RGB image by R. Jay GaBany shows how the dust lane of NGC 891 is full of pink nebulae. Note the "dust chimneys", columns of dust rising vertically from the dust lane. They may be formed by exploding supernovae.

Finally, let's look at the "mother of all starforming edge-on galaxies", NGC 4631. This image by R. Jay GaBany was an APOD. But no matter how you look at this galaxy, its star formation is overwhelming. Look at this. Or this. This is a combined Hubble and Chandra image of NGC 4631. What you can see in red is the churning, star forming disk of NGC 4631, and the blue "cloud" surrounding the galaxy is an X-ray halo produced by large numbers of hot young stars and supernovae in this galaxy.

So my point remains: The star formation rates of different galaxies vary. NGC 3628 is probably poor in star formation.

Ann
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