Starship Asterisk*

The Infrared Visible Andromeda

Explanation: This remarkable synthetic color composite image was assembled from archives of visible light and infrared astronomy image data. The field of view spans the Andromeda Galaxy (M31), a massive spiral a mere 2.5 million light-years away. In fact, with over twice the diameter of our own Milky Way, Andromeda is the largest nearby galaxy. Andromeda's population of bright young blue stars lie along its sweeping spiral arms, with the telltale reddish glow of star forming regions traced in space- and ground-based visible light data. But infrared data from the Spitzer Space Telescope, also blended directly into the detailed composite's red and green color channels, highlight the the lumpy dust lanes warmed by the young stars as they wind even closer to the galaxy's core. Otherwise invisible at optical wavelengths, the warm dust takes on orange hues. Two smaller companion galaxies, M110 (below) and M32 (above) are also included in the frame.

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Andromeda is one of my favorite objects in the near universe; but I had never seen in such colors. Thank you!

There's a visible / infrared toggle available on Rob's site. It's easy to miss.
http://www.robgendlerastropics.com/M31- ... eover.html

Disclaimer: I helped make the script so of course I have to persuade people to use it.

geckzilla wrote:There's a visible / infrared toggle available on Rob's site. It's easy to miss.
http://www.robgendlerastropics.com/M31- ... eover.html
Disclaimer: I helped make the script so of course I have to persuade people to use it.

Thank you VERY much indeed for that link. It gives wonderful insight into the structure of M31. Great!

Viewed in infrared, Andromeda resembles a ring galaxy. Might it actually be a ring galaxy rather than a classic grand design spiral?

Bruce

Thanks judy for the script! A couple of comments. Yes M31 does seem to posess a spiral-ring structure in infrared.
See the article below. Apparently the ringed nature may be related to previous interactions with its satellite galaxies.
http://iopscience.iop.org/1538-4357/638 ... _2_L87.pdf

The other comment is how I made the image. I was looking for a way to highlight the infrared appearance but
also create a pleasing blend with the visible light view of M31. Simply layering the Spitzer data over M31
in various modes (lighten, etc.) didn't achieve what I was looking for. Eventually I found that incorporating
the 24um data into the red and green channels produced the aesthetic blend I was looking for. It also
produced the yellow-reddish color that contrasted perfectly with the blue visible light color of the
galaxy. So there was no actual science involved in the creation of the composite, just strategies to
highlight the IR data in an aesthetically pleasing and noticeable manner. The infrared data is 24um
data from Spitzer. There was also 4.5 to 8.0 um data which revealed an abundance of stars not apparent
in visible light. I made an attempt to incorporate this as well but registering this data to the visible light
stars proved impossible.

rgendler wrote:So there was no actual science involved in the creation of the composite, just strategies to
highlight the IR data in an aesthetically pleasing and noticeable manner.

Perhaps the process was primarily aesthetic, but the information you provide allows viewers so inclined to get a lot of scientific information from the image. Thanks for that!

geckzilla wrote:There's a visible / infrared toggle available on Rob's site. It's easy to miss.
http://www.robgendlerastropics.com/M31- ... eover.html ...

I like how it's the dark dust lanes that light up in IR.

BDanielMayfield wrote:Viewed in infrared, Andromeda resembles a ring galaxy. Might it actually be a ring galaxy rather than a classic grand design spiral?

Bruce

I don't think Andromeda is a classic grand design galaxy at all. It is a ring galaxy, although not necessarily one that resembles many other ring galaxies. Take the Cartwheel galaxy, for example, which is the product of a galactic collision. Another galaxy has passed through the disk of the Cartwheel galaxy and the "splash" has made the galaxy ripple like the surface of a pond when you throw a stone into it.

But the Cartwheel galaxy has "spokes" between the inner and outer bright rings. The Andromeda galaxy has no spokes. But it could be that the "pebble" hasn't yet "hit" the surface of the Andromeda galaxy. The "pebble" might be M32, the small satellite galaxy that is seen at 11 o'clock in Rob Gendler's picture. Perhaps, when M32 has passed through the disk of Andromeda, the ripples might get stronger, the rings may get more pronounced and spokes might appear, too.

Ann

rgendler wrote:Thanks judy for the script! A couple of comments. Yes M31 does seem to posess a spiral-ring structure in infrared.
See the article below. Apparently the ringed nature may be related to previous interactions with its satellite galaxies.
http://iopscience.iop.org/1538-4357/638 ... _2_L87.pdf

Thanks Robert, both for your work product and for your response.

Ann wrote:

BDanielMayfield wrote:Viewed in infrared, Andromeda resembles a ring galaxy. Might it actually be a ring galaxy rather than a classic grand design spiral?

Bruce

I don't think Andromeda is a classic grand design galaxy at all. It is a ring galaxy, although not necessarily one that resembles many other ring galaxies. Take the Cartwheel galaxy, for example, which is the product of a galactic collision. Another galaxy has passed through the disk of the Cartwheel galaxy and the "splash" has made the galaxy ripple like the surface of a pond when you throw a stone into it.

Ripples on a pond does seem like an apt analogy, but what is the medium that is carrying the ring of dust outward in Andromeda? Is this a pressure wave, or perhaps something else?

Bruce

geckzilla wrote:There's a visible / infrared toggle available on Rob's site. It's easy to miss.
http://www.robgendlerastropics.com/M31- ... eover.html

Disclaimer: I helped make the script so of course I have to persuade people to use it.

Judy and/or Rob, does the ir data cover the satellite galacy M32 as well? If so, that galaxy seems completely devoid of any ir signal at all.

BDanielMayfield wrote:Ripples on a pond does seem like an apt analogy, but what is the medium that is carrying the ring of dust outward in Andromeda? Is this a pressure wave, or perhaps something else?

I wouldn't take the analogy too far. I doubt anything is actually moving outward. Structures like this are more likely to be shock fronts of some kind, and essentially stationary.

BDanielMayfield wrote:

geckzilla wrote:There's a visible / infrared toggle available on Rob's site. It's easy to miss.
http://www.robgendlerastropics.com/M31- ... eover.html

Disclaimer: I helped make the script so of course I have to persuade people to use it.

Judy and/or Rob, does the ir data cover the satellite galacy M32 as well? If so, that galaxy seems completely devoid of any ir signal at all.

I'm no expert but I believe dwarf elliptical galaxies emit mostly in the far IR which arises
mostly from cold molecular clouds. The APOD composite was made with 24um data which
I believe falls in the mid IR range and arises in areas of active star formation and is therefore
warmer. Perhaps a professional astronomer or someone who knows more can elaborate.
Below is a short piece on far IR emission from dwarf ellipticals (ie; M32, M110)
http://ned.ipac.caltech.edu/level5/Marc ... fs3_2.html

Chris Peterson wrote:

BDanielMayfield wrote:Ripples on a pond does seem like an apt analogy, but what is the medium that is carrying the ring of dust outward in Andromeda? Is this a pressure wave, or perhaps something else?

I wouldn't take the analogy too far.

Yes, that's why I wrote 'seem's like' instead of 'is an apt analogy'.

I doubt anything is actually moving outward. Structures like this are more likely to be shock fronts of some kind, and essentially stationary.

Interesting. What's causing the shock then? It does look like dust is being piled up from an outward moving force somehow.

BDanielMayfield wrote:

Chris Peterson wrote:I doubt anything is actually moving outward. Structures like this are more likely to be shock fronts of some kind, and essentially stationary.

Interesting. What's causing the shock then? It does look like dust is being piled up from an outward moving force somehow.

When I see unusual structure in galaxies, I usually assume a collision or interaction. So that means gravity is the force involved, most likely in the form of tides.

BDanielMayfield wrote:

geckzilla wrote:There's a visible / infrared toggle available on Rob's site. It's easy to miss.
http://www.robgendlerastropics.com/M31- ... eover.html

Disclaimer: I helped make the script so of course I have to persuade people to use it.

Judy and/or Rob, does the ir data cover the satellite galacy M32 as well? If so, that galaxy seems completely devoid of any ir signal at all.

The way I understand it, dwarf elliptical galaxies (containing only old stars and little dust) emit very little far infrared light at all. They do emit a lot of near infrared light, because they are full of old red stars, which are much brighter in near IR than in optical light. But to get a lot of far infrared light I think you need a lot of dust, and, not least, quite a bit of star formation.

So it makes sense to me that M32 would be very faint indeed in far infrared or even mid infrared light. On the other hand, there really is some dust and some relatively young stars in the other obvious Andromeda satellite, NGC 205. This picture, which just might be an Adam Block image, shows the bluish central part and the two dust clouds in NGC 205 quite well.

Ann

A wonderful photo composition, but he descriptive text is misleading where it says

... young stars as they wind even closer to the galaxy's core.

Galaxies do not work like hurricanes - the spiral arms are not flowing into the core of the galaxy. The stars in the galaxy are in orbit around the center of the galaxy in the same sense as the planets are in orbit around the Sun. In fact it was discrepancies in the orbital velocities of the stars vs. their distance from the galactic center that led to the hypothesis about the extended halo of dark matter surrounding the galaxies.

Charley wrote:A wonderful photo composition, but he descriptive text is misleading where it says

... young stars as they wind even closer to the galaxy's core.

Galaxies do not work like hurricanes - the spiral arms are not flowing into the core of the galaxy. The stars in the galaxy are in orbit around the center of the galaxy in the same sense as the planets are in orbit around the Sun. In fact it was discrepancies in the orbital velocities of the stars vs. their distance from the galactic center that led to the hypothesis about the extended halo of dark matter surrounding the galaxies.

Granted, the wording is somewhat ambiguous. What I read is

...highlight the the lumpy dust lanes warmed by the young stars as they wind even closer to the galaxy's core.

That is, the dust lanes are winding even closer to the core, not the stars. While it could be read either way, I'm quite sure the editors meant it the way I've presented, since they know how galaxies work, and there have been many discussions in this forum about the orbital dynamics of stars in spiral galaxies.

Chris Peterson wrote: ... the dust lanes are winding even closer to the core, not the stars. While it could be read either way, I'm quite sure the editors meant it the way I've presented, since they know how galaxies work, and there have been many discussions in this forum about the orbital dynamics of stars in spiral galaxies.

Does dust and gas in spiral galaxies really spiral in toward the center? (This question is sincere. My motive is to improve my understanding of how things really work.) I would have thought that dust clouds would orbit around galactic centers basicly just like stars do, except for changing shape, etc.

BDanielMayfield wrote:

Chris Peterson wrote: ... the dust lanes are winding even closer to the core, not the stars. While it could be read either way, I'm quite sure the editors meant it the way I've presented, since they know how galaxies work, and there have been many discussions in this forum about the orbital dynamics of stars in spiral galaxies.

Does dust and gas in spiral galaxies really spiral in toward the center? (This question is sincere. My motive is to improve my understanding of how things really work.) I would have thought that dust clouds would orbit around galactic centers basicly just like stars do, except for changing shape, etc.

Neither the dust nor the gas move towards the center. The lanes, however, are structures which can be reasonably said to wind closer to the core (or away from the core, if you prefer). That's what defines a spiral. This is a reference to the visual appearance, not the dynamics.