Spitzer's Milky Way (APOD 05 Jun 2008)

[Andy Wade]

http://antwrp.gsfc.nasa.gov/apod/ap080605.html

Now that's what I call an amazing picture. I guess what is really special is that it's our own galaxy. I'm used to seeing pictures of other galaxies but never our own, all in one shot.
Marvellous stuff! Thanks to the APOD team for showing this one. Well done chaps!
Assuming that the galactic centre is right in the middle, there are two large masses of white at either end, they are only visible on the large picture linked from the APOD picture. The right hand one is obvious but the left hand one is only partly photographed at the bottom edge of the picture. They look significant and I wondered what they were called?

[JohnD]

It's NOT the whole galaxy, Andy!
Only about 8 degrees worth!
"The whole image is 120 degrees wide"

But you are right what an image.
What is the conglomeration in the centre?
Is it the Core?
John

[kjardine]

Andy, the object on the left (partially visible on the linked image) is the Lagoon nebula (M8, Sh 2-25), and the one at the right is the War and Peace nebula (NGC 6357, Sh 2-11, W22).

Both look quite impressive in infrared.

John - yes the image is centred on the galactic nucleus.

Kevin

Kevin Jardine
Galaxy Map
http://galaxymap.org

[BMAONE23]

HERE is a link to the Spitzer Web Page with the entire mosaic. HUGE IMAGES

[kjardine]

In case anyone is wondering what they are seeing when they look at the Spitzer mosaic, I've uploaded a labelled diagram I did of the MSX data a while back.

MSX is a less detailed but more comprehensive infrared survey of the entire galactic plane from +5 to -5 degrees in latitude. It is also useful as a guide to the Spitzer data, and my file (linked at the end of this message) is reduced to a tenth of the original width and height.

I actually have the full MSX dataset plus a lot else up at my Galactic Plane Explorer here:

http://galaxymap.org/drupal/node/92

but if you want a graphic image you can download and view offline, you can find the link at the end of this message. Warning, this is a 21600x600 pixel 22 megabyte file even at its reduced size and may crash your browser if you try viewing it directly. So I suggest that you right click the link and save it to your hard drive.

The references are mostly to the Sharpless, Gum and RCW catalogs described here:

http://galaxymap.org/drupal/node/33

OK, as promised here's the link to the big 22MB file with the labelled nebulae:

http://galaxymap.org/book_images/msx_small_labelled.png

Kevin

Kevin Jardine
Galaxy Map
http://galaxymap.org

[jimsaruff]

Great stuff, Kevin!

Recently I read that astronomers no longer believe there are four major arms in our galaxy. I know you are completely familiar with this. But wanting to make all things accessible, here is the story:

http://www.sciencedaily.com/releases/20 ... 160245.htm

My question for you is: Can we see the two major arms in the 120 degree mosaic? If so, can you point to them for us, or for me anyway?

Thanks for your time and your blog is a great read, btw.

Jim

[henk21cm]

but if you want a graphic image you can download and view offline, you can find the link at the end of this message. Warning, this is a 21600x600 pixel 22 megabyte file

Huge indeed. An image of a type i have never seen before. So many details that i do not know where to start looking in the first place. And so many questions. To start: what am i looking at? Stars? Nebulae?

Why are the Sh 2 numbers more or less evenly spread?
What kind of items are the Wnumber?
Why have some both a Sh 2 and and a W number?
What are BFS? Why are they not in the center?
The G objects are about 30 degrees from the center. The galactic coordinates are stored in their names. What kind of objects are those?

I suppose this image is a false colour image, since it refers to UV.
Is white bright and hot? Black is dust?
Are the blue objects individual stars, or just noise?

Some of the Sh2 objects, e.g. Sh 2-235 look like tiny spiral arm galaxies. The chance to see those in the plane of our own galaxy are minute. Why do they look like spiral arm galaxies?

Some items, like W16, look like planetary nebulae or puffs of gas from unstable stars. Is that correct?

Why are not the locations of objects evenly distributed, apart from the center? There are definitely lumps, e.g. at 80 degrees, 110 and 290 degrees. Are these locations where the arms of our own galaxy are found?

[kjardine]

Hi Jim,

In the Spitzer image you can see objects in the Scutum-Centaurus arm and in the Sagittarius, Carina and Norma arcs. (I'll call them arcs now that they are not recognised - at least by NASA - as full arms.)

You can't see the Perseus arm in the Spitzer images as it is too far away and obscured in that area - except perhaps very faintly at around 60 to 65 degrees. The best view of the Perseus arm is in the outer galaxy and Spitzer has not imaged that.

As you may know, I've published a face-on map of the Milky Way on my site based on distance estimates for about 9000 objects, and there is no obvious trace of a coherent arm or arc in the Sagittarius region. Just a jumble of different objects at different distances. So I was delighted to see the recent research questioning whether a full Sagittarius arm exists because it solves a big mystery.

Kevin

Kevin Jardine
Galaxy Map
http://galaxymap.org

[kjardine]

Hi Henk,

Most of your questions are answered on my site.

I'd start with these three articles:

http://galaxymap.org/drupal/node/33

http://galaxymap.org/drupal/node/32

http://galaxymap.org/drupal/node/90

In terms of the concentrations that you noticed. Yes, they are all connected to major Milky Way structures.

At 80 degrees you are looking down the Orion Spur into Cygnus, and since you are looking right into the Spur and not just across it, you see more objects.

At 110 degrees you are looking at Cas OB2, one of the largest star formation regions of the Perseus arm. It's an especially dusty star association, so you see a lot of galactic "smog" that shows up well in infrared. Cep OB1, another important part of the Perseus arm, is nearby.

See my commentaries here:

http://galaxymap.org/drupal/node/105

and here:

http://galaxymap.org/drupal/node/106

for more on these.

290 degrees is the centre of the Carina arc, including the Eta Carinae nebula. Again, you are looking right down the arc, so you see a lot of objects.

[iamlucky13]

HERE is a link to the Spitzer Web Page with the entire mosaic. HUGE IMAGES

There's more viewing options here, including a Google maps-style viewer with zoom and panning:
http://www.spitzer.caltech.edu/Media/re ... info.shtml

It's NOT the whole galaxy, Andy!
Only about 8 degrees worth!
"The whole image is 120 degrees wide"

And that's not even the whole galaxy, just the best part.

I suppose this image is a false colour image, since it refers to UV.
Is white bright and hot? Black is dust?
Are the blue objects individual stars, or just noise?

IR actually, not UV. The press release says blue is 3.6 micron, green is 8 micron, and red is 24 micron. This is 3-5 octaves below visible light.

I believe white would mean relatively evenly mixed in those wavelengths, which could include hot objects. Black would most likely be relatively cold dust, and I think the blue objects are mostly individual stars.

By the way, the caption notes that the image was revealed at the meeting of the American Astronomical Society. I've been told it's a 180 foot long print hanging on the wall with a width of 400,000 pixels. That equates to 185 dpi, so even at that huge scale, the print has better resolution than a computer monitor!

Kevin, I can't view your huge images at the moment, but I plan to. They sound very detailed.

[kjardine]

Hi Jim,

I've looked more carefully at the Spitzer mosaic and I have to say I was wrong about the visibility of the Perseus arm. You can actually see several prominent first quadrant Perseus arm objects including W49 (at 43 degrees) and 3C 397W (at 41 degrees).

So even though the Perseus arm is more visible in the second quadrant (90 to 180 degrees, outside the range of the Spitzer data), the Spitzer imaging is sensitive enough to pick up the Perseus arm in the first quadrant, especially between 40 and 65 degrees.

To see these, go to:

http://mipsgal.ipac.caltech.edu/iracmips_map.html

and enter 41 or 43 in the "l" box next to "Go to".

Kevin

Kevin Jardine
Galaxy Map
http://galaxymap.org

[henk21cm]

Most of your questions are answered on my site.

I browsed your site and read very interesting details. Nice to see the old Dwingeloo telescope. FYI: it has been decomissioned a few years ago and donated to 'the public'. There is a foundation, by amateur astronomers and radio amateurs, with plans to fix it (currently chipping rust, painting) and put it back into operation. http://en.wikipedia.org/wiki/Dwingeloo_ ... bservatory

At 80 degrees you are looking down the Orion Spur into Cygnus, and since you are looking right into the Spur and not just across it, you see more objects.

The 2008-06-06 APOD was helpfull and an old 21 cm map of the milky way, to understand the orientation and structure. Your explanation leaves me with yet another question. A similar situation: looking into the ?Spur? should occur when looking at 290 degrees (unnamed arm or fragment) and 310 degrees (Carina arm). At least the distance to the Carina arm and the Perseus arm at 80 degrees is comparable. So i expect to see a similar concentration of objects, reflecting nebulae. The unnamed arm or fragment at 290 degrees is even closer than the Perseus arm. When an object is at the same distance or even closer than another object, it should have the same size or it is even larger. That is under the assumption that the objects are comparable in properties.

If i assume that the Carina arm and the Perseus arm have similar properties -apart from their location-, their sizes must be the same. However when i compare the size of the concentrations of objects at 80 degrees, -nearly the entire height of the image- to the size of the concentration of objects at 290 and 310 degrees -nearly half the height of the image- the large difference is striking. The difference in height suggests either that the Carina arm is further away than the Perseus arm, or the assumption that the properties are the same, is incorrect.

A possible explanation is that we look into the tail of the Perseus arm and the head of the Carina arm. The arms may be conically shaped: narrow at the head and wider at the tail.

Another symmetry related remark. For me it is the first time that i hear and see that our galaxy is a barred system. About the orientation of the bar -assuming it is correct- as drawn in the 2008-06-06 APOD i have some doubts. When i look at the central part of the tapered image, there is a large concentration of objects between 30 and 327 degrees, or 30 and -33 degrees. If the bar is not perpendicular to the line sun-center (that would be a sheer coincidence), due to difference in distances i expect an asymmetrical distribution around 0. In this case there is some asymmetry, suggesting that the bar at 'negative' galactic longitudes is closer to the sun than the bar at positive longitudes. Yet the bar is drawn in such a way that at positive longitudes it is closer to the sun than at 'negative' (>300 degrees) longitudes.

So either i am overlooking some details or the longitudes as drawn on the 2008-06-06 APOD are flipped.

Carina arm ?=? Scutum Centaurus arm?

[henk21cm]

IR actually, not UV. The press release says blue is 3.6 micron, green is 8 micron, and red is 24 micron. This is 3-5 octaves below visible light.

Oops, my mistake. Wave lengths comparable to every days weather satelite images (3.9 (fog, stratus), 6.2 (water vapour) and 10.8 (cloud top) μm)

[Case]

It is the first time that i hear and see that our galaxy is a barred system.

APOD 2005-08-25

[iamlucky13]

IR actually, not UV. The press release says blue is 3.6 micron, green is 8 micron, and red is 24 micron. This is 3-5 octaves below visible light.

Oops, my mistake. Wave lengths comparable to every days weather satelite images (3.9 (fog, stratus), 6.2 (water vapour) and 10.8 (cloud top) μm)

Looks like snow is in the forecast for the inner Perseus Arm then!