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

[Ann]

Geck wrote:
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.

Indeed, as I looked through Wray's The Color Atlas of Galaxies I, too, noted NGC 1672, of course. I just didn't think it was really similar to NGC 2903. To me, NGC 2903 seems to have a disk that is relatively "flat", but the spirals arms or dust features crossing the bar seem to be out of plane. I don't think NGC 1672 looks like that, but instead it seems to be more like NGC 3187, where the arms and the bar are located in entirely different planes, quite unlike NGC 2903.

So to me, M108 is the galaxy that most closely resembles NGC 2903, where the disk seems to be relatively "flat", but some dust features are put of plane. However, NGC 1672 may be more interesting and more similar to NGC 2903 than it appears to be to me. Do you have a good picture of the bar of NGC 1672, Geck? And do those infrared images show spiral features - not just minor dust features - that are crossing and partly hiding the bar? Note that dust features that seem to radiate outwards from the bar are quite common in barred galaxies, but they don't hide the bar.

Ann

[geckzilla]

I'm just looking at them with Aladin. Useful software. Here are screenshots. The brightnesses between the two galaxies might not be comparable. I'm not really sure how these all sky maps deal with the large range of bright objects across the sky. Anyway, the point is to look at the structures and and not the brightness. What I see is two bars whose structures are not necessarily representative of the entire structure of the galaxy. You've got dust lanes crossing in front of both seemingly unaffected by whatever process created the bar. It's just easier to see in NGC 2903. NGC 1672 has its own peculiar aspects. I'm not really sure how you can judge NGC 3187 as being more similar since it is edge on. You note the shape of the arms in 1672 as being a little different from 2903 but you can't even see the shape of the arms in 3187. It's just an edge-on blobby mess.

[rstevenson]

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

No, I chose NGC 1300 because it had such a clear and simple structure, making obvious the dust crossing the bar, thus allowing me to make my point. Whereas in visible light at least, NGC 1672 appears not to have a bar at all, though I know there is one, made more obvious in IR. So, allow me to make my points the way I want to, and you make yours as you wish.

Rob

[geckzilla]

Sorry if I missed your point. Not sure why you'd snap back at me for it.

[Ann]

Thanks, Geck, interesting.

There are all sorts of dust lanes associated with bars. There are, for example, some interesting longitudinal dust lanes in the elongated bar of NGC 2523 - I tried to find a good picture of this galaxy, but I found nothing on the net that was better than James D Wray's old UBV image from 1979. Indeed, all sorts of dust lanes are associated with bars - this large image by Adam Block shows one example, NGC 1530. Another good example (and large picture, unfortunately) is NGC 1097 by Robert Gendler and ESO.

But what makes the bar of NGC 2903 unique to me is that the bar is so long, so yellow, so different in color from the spiral arms, and the fact that a sharply defined yellow piece of it sticks out on the other side of what appears to be a spiral arm. I haven't seen that anywhere else, in any other galaxy.

I'm a stickler for color, as you know, Geck. In NGC 2903 I see something that is glaringly apparent in RGB as well as in UBV images. It may not be obvious at all in infrared images or in general black and white images, but that doesn't mean that the feature isn't there.

After all, you wouldn't accept it if I said that an infrared feature isn't important just because it can't be seen in RGB.

Ann

[geckzilla]

I don't just mean dust lanes associated with bars. I drew a picture to help illustrate what I mean. Here, the orange represents the bar portion which has a clearly straight line emanating from the nucleus and bends somewhat abruptly into arms. Meanwhile, other structures of the arms such as younger stars and dust lanes do not follow the bar pattern, represented here with blue and black lines. This is a fictional galaxy.

[bystander]

...
This is a fictional galaxy.

Which galaxy is it? Is it a galaxy far, far away?

Click to play embedded YouTube video.

[Ann]

This is going to be my last post here, I promise.

Geck, you just helped me put my finger on what is so strange about the bar of NGC 2903, and what it is that makes it different from the bar of your fictional galaxy. The galaxy you drew has a bar whose bar endings bend up or down in the same directions as the nearby spiral arms. The bar end on the left bends upwards, just like the nearby spiral arms, and the bar end on the right bends downwards, like the nearby spiral arms.

That is what the bar of NGC 2903 doesn't do. Its "left" bar end (in the APOD) really does bend upwards, just like the adjacent spiral arms. But its "right" bar end doesn't. It sticks out, straight and yellow, beyond the spiral arms, and then just abruptly ends.

That is what makes the bar of NGC 2903 unique, as far as I know.

Ann

P.S. Nice song, bystander.