APOD: NGC 2903: A Missing Jewel in Leo (2015 Apr 10)

[APOD Robot]

NGC 2903: A Missing Jewel in Leo

Explanation: Barred spiral galaxy NGC 2903 is only some 20 million light-years distant. Popular among amateur astronomers, it shines in the northern spring constellation Leo, near the top of the lion's head. That part of the constellation is sometimes seen as a reversed question mark or sickle. One of the brighter galaxies visible from the northern hemisphere, NGC 2903 is surprisingly missing from Charles Messier's catalog of lustrous celestial sights. This colorful image from a small ground-based telescope shows off the galaxy's gorgeous spiral arms traced by young, blue star clusters and pinkish star forming regions. Included are intriguing details of NGC 2903's bright core, a remarkable mix of old and young clusters with immense dust and gas clouds. In fact, NGC 2903 exhibits an exceptional rate of star formation activity near its center, also bright in radio, infrared, ultraviolet, and x-ray bands. Just a little smaller than our own Milky Way, NGC 2903 is about 80,000 light-years across.

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[geckzilla]

Doesn't it look like that bright, bar-like structure is actually behind the galaxy?

[Chris Peterson]

Doesn't it look like that bright, bar-like structure is actually behind the galaxy?

It does, sort of. But that would be impossible. The processing on this image is deceptive, massively flattening the dynamic range. In terms of the actual photometry, the center is orders of magnitude brighter than the outer parts. It doesn't look like it here, but it's far too bright for anything behind the galaxy to shine through.

[geckzilla]

I did look up other images of NGC 2903 before making that post. Here's an SDSS view. The bar is more natural looking but it still also strangely looks as if it is non-interacting with the galaxy itself. I dunno. I wouldn't put it an especially high probability that it is a background object. It's just odd-looking.

[Ann]

Doesn't it look like that bright, bar-like structure is actually behind the galaxy?

It does, sort of. But that would be impossible. The processing on this image is deceptive, massively flattening the dynamic range. In terms of the actual photometry, the center is orders of magnitude brighter than the outer parts. It doesn't look like it here, but it's far too bright for anything behind the galaxy to shine through.

James D Wray, The Color Atlas of Galaxies (1988), wrote:

A distinct yellow bar crosses the disk of this galaxy, but because its structure is everywhere patchy and broken it is practically undetectable as a morphological entity (i.e. 'bar') without recourse to color information.
..
Whatever its cause it seems appropriate to refer to the effect in the image as a 'color bar' because without the awareness of the color property the bar property is masked by the patchy structure which otherwise could be taken simply for bright regions of star formation in the spiral arms.

The bar of NGC 2903 is a color bar. James D Wray never applied any stretching to his images, so they give a true portrait of the brightness distribution of the galaxies he photographed. His two images of NGC 2903 show the patchy central part of the galaxy to be overexposed and white. The rather small bulge around the patchy overexposed center is yellow. The color bar is fascinatingly yellow and broken by dust. The spiral arms on one side of the bar ('below' the bar in today's APOD) are patchy with bluish knots, whereas the spiral arms on the other side of the bar ('above' the bar) are mostly darkly yellowish.

I found it fascinating to see what the center of the galaxy looks like in today's APOD. It is bursting with young blue stars and pink emission nebulas.

Ann

[MadMan]

Geckzilla - I had the same question when I saw this image. It seems like the spiral arms are usually attached to the ends of the bar, but in this case, it appears that the spiral arms don't "notice" the bar.

[MadMan]

Maybe we are seeing very early or very late in the life of the bar?

[rstevenson]

A couple of years ago, our very own geckzilla did a version of the center of NGC 2903 based on HST data. It gives a much different view of the bar, removing, I think, any doubt as to its being part of the galaxy.

Rob

[Boomer12k]

It looks, from this image, that there are TWO bars...not connected in the center, and the spiral arms appear over the top of them...it is most interesting, like TWO galaxies at the ENDing stages of their collision, and it has settled down quit a bit, but you still have lots of star formation. It would be interesting to see any star streams, as stars look to fill the voids between the arms, in the large gaps...but it is probably just me...other shots look lots different.

:---[===] *

[geckzilla]

A couple of years ago, our very own geckzilla did a version of the center of NGC 2903 based on HST data. It gives a much different view of the bar, removing, I think, any doubt as to its being part of the galaxy.

Rob

It actually doesn't for me. I looked at my own picture too (I think I should reprocess that image, bar aside) and it's just really hard for me to shake the interpretation that it's a streak wholly behind the dust rather than intermingling with it.

[Ron-Astro Pharmacist]

http://en.wikipedia.org/wiki/Barred_spiral_galaxy

From above.

…Bars are thought to be temporary phenomena in the lives of spiral galaxies; the bar structures decay over time…

Could the bar in this galaxy be on the decline?

[Chris Peterson]

It actually doesn't for me. I looked at my own picture too (I think I should reprocess that image, bar aside) and it's just really hard for me to shake the interpretation that it's a streak wholly behind the dust rather than intermingling with it.

A streak that appears behind the dust isn't quite the same as a streak that appears behind the galaxy, however. It is easier to explain the former as a physical reality, and not merely an illusion.

[Just Jackson]

So, does anyone know why / how these bars form? Last I heard, it was a mystery.

[Chris Peterson]

So, does anyone know why / how these bars form? Last I heard, it was a mystery.

It's not fully understood, but neither is it a complete mystery. They appear to be created by a complex interaction between star formation and density gradients caused by gravitational resonances. The fact that they occur in simulations allows the mechanisms to be explored.

[Craine]

I found this link interesting:
http://hubblesite.org/hubble_discoverie ... lution.pdf

[FloridaMike]

...a complex interaction between star formation and density gradients caused by gravitational resonances...

AKA , Bartenders..

[Ann]

It actually doesn't for me. I looked at my own picture too (I think I should reprocess that image, bar aside) and it's just really hard for me to shake the interpretation that it's a streak wholly behind the dust rather than intermingling with it.

A streak that appears behind the dust isn't quite the same as a streak that appears behind the galaxy, however. It is easier to explain the former as a physical reality, and not merely an illusion.

I looked through James D Wray's The Color Atlas of Galaxies to see if I could find any sort of match to NGC 2903. No luck, however. And that is not surprising, given how interested James D Wray was in the bar of NGC 2903.

But Wray's atlas really shows a lot of galaxies with weird and warped spiral arm configurations. I'm sure Chris is right that in NGC 2903 the bar is behind an out-of-plane dust lane belonging to a spiral arm, but it is not behind the galaxy proper.

Searching elsewhere, I did find a picture of a galaxy that has some interesting similarities to NGC 2903, however. I'm sorry that the only picture I could find of this galaxy, NGC 1808, is so big - over 1,000 KB. Nevertheless, please note the brilliantly starbursting center which is stirring up the dust and the spiral arms of NGC 1808.

Ann

[Boomer12k]

AND....GREAT WORK TONY!!!!!!!!!!!!

He helped me with some of my pictures.
:---[===] *

[Dad is watching]

I took this image and converted it to 8-bit grey scale to see if I could get a better look at the 'bar'. What I found was that the left half of the bar virtually disappeared and the hi-lites seemed to align with the inner arms of the spiral. The right side of the 'bar' seems to curve toward the bottom of the image as it approaches the central region and hi-lites of the 'bar' seemed to follow along the arms as well. Neither one seems to bisect the galaxy center and the 'bar' itself seems to lack any real structure. Are we looking at an optical illusion cause by the angle we are viewing it at, and by lighting and shadow?

[Ann]

I took this image and converted it to 8-bit grey scale to see if I could get a better look at the 'bar'. What I found was that the left half of the bar virtually disappeared and the hi-lites seemed to align with the inner arms of the spiral. The right side of the 'bar' seems to curve toward the bottom of the image as it approaches the central region and hi-lites of the 'bar' seemed to follow along the arms as well. Neither one seems to bisect the galaxy center and the 'bar' itself seems to lack any real structure. Are we looking at an optical illusion cause by the angle we are viewing it at, and by lighting and shadow?

The bar is not an illusion. A gray scale may not show it, but a color picture will. Most bars are old and yellow, and the bar of NGC 2903 is bright, old and yellow. A color picture will clearly show that the stellar population in the bar is distinctly different from the stellar populations in the spiral arms.

Ann

[geckzilla]

It's a little baffling to me how the dust and star forming regions completely ignore the bar and appear as a continuous spiral overlapping the bar. It is something I have never noticed before but seems to be typical for bars so this is a normal example rather than an exception.

[rstevenson]

It might help to take a look at NGC 1300, since it's aligned so we can see its bar clearly from above/below...

We can see that the bar is a clearly delineated structure within the galaxy, but that it also has overlying filaments of gas and dust, with lots of star formation occurring in nearby spiral arms.

But NGC 1300 has a much simpler structure than NGC 2903, with much more room between the spiral arms and the bar. From this POV, it's tempting to picture it as a single thin layer. But like all galaxies, it's not that thin. There's lots of vertical depth in a galaxy, and lots of gas and dust can slide over and under the arms and the central bar.

Probably NGC 2903 has been disrupted fairly recently by a galaxy merger, stirring things up and setting off the large amount of star formation we see. With lots of data and some excellent modeling, we might be able to deduce the approximate mass and the direction of passage of the disrupting galaxy.

Rob

[geckzilla]

You might find a more appropriate analogue in NGC 1672. http://apod.nasa.gov/apod/ap070418.html

[Ann]

It's a little baffling to me how the dust and star forming regions completely ignore the bar and appear as a continuous spiral overlapping the bar. It is something I have never noticed before but seems to be typical for bars so this is a normal example rather than an exception.

I don't think the bar of NGC 2903 is typical. I think it is weird.

You will forgive me for once again referring to James D Wray's The Color Atlas of Galaxies. In that atlas, Wray very often compared galaxies with one another. So, for example, Wray wrote about NGC 2841:

The broad outer disk is similar to that of NGC 2775, although long dust lanes are more in evidence here.

He wrote about NGC 2959:

Compare with NGC 2787 and NGC 936.

So Wray often asked his readers to understand a galaxy better by looking at a picture of another galaxy that is similar to it. (That, by the way, is why I often like to point out other galaxies that are similar to this or that galaxy portrait of this or that APOD - I try to take after James D Wray.)

But Wray could see no counterpart to the bar of NGC 2903. I really think that the bar of NGC 2903 is highly unusual. However, I think there just might be a counterpart, and that might be M108, NGC 3556. According to Wikipedia, M108 is a barred galaxy, and photographs show it to have a disturbed disk with out-of-plane dust features.

Tammy Plotner wrote about M108:

Located about 45 million light years away from Earth and running away from us at 772 kilometers per second, this disturbed looking galaxy is rich in dark dust, star forming regions and a supershell.
...
“Since this galaxy is isolated, the supershells are unlikely to have been created through impacting external clouds, yet the required input energy is also greater than that available from the observed internal star formation rate. Thus it would appear that some form of energy enhancement (such as magnetic fields) must also be important in creating these features. The supershells are so dominant that they distort the outer major axis.

Perhaps, if we had a more face-on view of M108, its bar might look a bit broken by the out-of-plane supershell.

Personally I don't think that NGC 2903 looks like it might be the product of a recent merger. Its outer features are far too "settled" and regular for that. Also M108 may or may not - probably not - be the product of a merger. But galaxies may have upheavals for other, more mysterious reasons. It's anybody's guess why isolated NGC 1313 is having the star formation chaos tantrum that it, in fact, does have.

So I don't think the weird bar of NGC 2903 is the product of a merger, although something strange has clearly occurred inside this galaxy.

Ann

[geckzilla]

It's a little baffling to me how the dust and star forming regions completely ignore the bar and appear as a continuous spiral overlapping the bar. It is something I have never noticed before but seems to be typical for bars so this is a normal example rather than an exception.

I don't think the bar of NGC 2903 is typical. I think it is weird.

You will forgive me for once again referring to James D Wray's The Color Atlas of Galaxies. In that atlas, Wray very often compared galaxies with one another.

. . .

But Wray could see no counterpart to the bar of NGC 2903. I really think that the bar of NGC 2903 is highly unusual. However, I think there just might be a counterpart, and that might be M108, NGC 3556.

Perhaps if Wray looked again with modern computer equipment and easy access to search through vast amounts of data, he would be more successful. Bars come in a few different styles and I have no problem finding images of galaxies with characteristics similar to NGC 2903. I already posted a link to NGC 1672 just before your post which has a similarly nebulous bar which is quite easily noticed in infrared observations but much more easily missed in other wavelengths. I agree that 2903 is at least a little weird, but it's not weird enough for me to say that there is no other bar similar to it. Really, the more I looked at NGC 2903, the less weird it seemed. The really weird objects tend to get even weirder upon further inspection.