Starship Asterisk*

dbenford, thank you very much for your detailed answers; much appreciated!

I'm a member of the WISE science team, and will try to answer some of the questions I've seen here. Please bear in mind, however, that we're still very much in the early days of the data processing and a full understanding of the overall system performance won't be had for many months. However, we are able to make multi-band mosaics of many, many frames such was demonstrated in the Andromeda image, and the overall accuracy of the images (astrometrically and photometrically) is quite good considering how soon after the start of the mission that the image was produced. I would also stress that my answers reflect my own opinions at the moment, and should not be taken as a definitive statement by the WISE mission or NASA.

First question: "But are some of those dots actually other galaxies in the far distance?" Yes, certainly. Which ones are, though, will take a long while to tease out. One of the reddest dots near M31, which is slightly above and to the right of center, appears to me to be an artifact from, perhaps, a cosmic ray hit or a latent image. It seems to appear in only one band (not impossible by any means, but potentially curious), and a quick look through some WISE frames seems to indicate that it's not always present. Sorry if that disappoints. I could well be wrong, however, and WISE should take another full set of Andromeda images later this year, thereby allowing us to confirm the validity of these sources. The brightest red thing to my eye is above and left of the center of M31, and that is an X-ray source found by ROSAT. It's within the optical 'border' of M31, but I don't believe it is known whether it is in fact associated with the galaxy or is an X-ray source at greater distance that just happens to be nearby.

"What are all the red dots?" This is a tough one. Some of them will be distant galaxies. Some may be concentrations of gas and dust that shine very brightly in the longer mid-IR wavelengths; however, they're very compact if in our galaxy and very luminous if associated with M31. Some may be other unusual objects in our galaxy. Some others may be artifacts of cosmic ray hits and latent images; this mosaic was produced without the whole suite of WISE data processing tools fully in place, and so some such things likely still remain. One of our tasks on the WISE science team is to comb through the data and ensure that we minimize any spurious objects. My guess (and that's all I have at the moment) would be that the "red dots" are mostly galaxies, but with a sprinkling of sources in our galaxy and perhaps some artifacts... and we're following up these sources to try to distinguish which things are dusty galaxies, which things are brown dwarfs, which things are star forming regions, etc. The WISE wavelength bands have been chosen specifically to enable the characterization and classification of all varieties of objects we anticipate seeing. (As an aside, the 22 micron band is actually a rather wide band, and so wavelengths somewhat shorter and longer are included in that image.)

"Does anyone else see a spiral structure in M110?" Well, I do see what you mean now that you mention it -- but then structure is often in the eye of the beholder. M110 is classified as a dwarf spheroidal or elliptical by various people who classify such things. It is, however, somewhat disturbed and so there is a bit of internal structure visible, which may be from dust lanes.

"what do we have if we compare the infrared to this picture? do the red dots you see correspond to what looks like a galaxy?" I did a by-eye comparison of these two and yes, there are faint visible-light dots where we have bright WISE red dots in some cases. Those are probably galaxies. I noted at least one that looked a bit smudgy in the visible, so that's a likely candidate.

"is it possible that the better resolution we use on the heavens could help make points of EM radiation stand out? would these red points of light be missed in other resolutions?" If I understood the question correctly, my answer is this: WISE has a better angular resolution than has been achieved in prior very large surveys at wavelengths such as 22 microns. It does, and will continue to, see many objects which are relatively faint and would not be noticed against brighter (often more local) sources if the images were blurred. So yes, points of light stand out quite well to WISE.

"How did all this come to be?" Andromeda is a rather warped spiral disk. You can see in the reddish colors that we see dust lanes quite distinctly (compare to the visible light image). These are regions where compression waves of material rotating in the galaxy end up triggering star formation. You're also noticing that there is greenish emission visible in distinct stripes, such as to the outer left of the galaxy. This is an indicator of clouds of gas being thrown around in the galaxy's rather disturbed rotation.

I'll leave the question on what we'd see from within M110 or M32, since I think that's been well-addressed by others.

Thank you for your interest in our mission and the Andromeda image. Further questions are always welcomed by the WISE science team!

RJN wrote:I have gone back and added a note to the bottom of the latest APOD page that "Canis Major's galaxy designation is now disputed" and linked it to this thread.

Thank you for that. I've just blogged about the Canis Major controversy here:

http://galaxymap.org/drupal/node/164

Thanks, Kevin, for your posts and scientific insight. On very rare occasions we will edit an old APOD. We try to avoid doing this for a variety of reasons including keeping our time commitment to APOD manageable, and preserving the historical integrity of old APODs. When things change, the idea is, we may write a new APOD.

Still, in this case, I have gone back and added a note to the bottom of the latest APOD page that "Canis Major's galaxy designation is now disputed" and linked it to this thread. That APOD can be seen here:
http://antwrp.gsfc.nasa.gov/apod/ap071104.html .

- RJN

Just for the record, I've added another comment to the talk page for the wikipedia article for the "Canis Major dwarf galaxy" listing 8 recent scientific papers concluding that the Canis Major "overdensity" is not caused by a dwarf galaxy or at least is more consistent with other explanations.

See:

http://en.wikipedia.org/wiki/Talk:Canis ... arf_Galaxy

Ah, I see. I've never tried to edit anything that others cared about, so I guess I've avoided all that. Now I'm forewarned.

Rob

RJN wrote:There was an APOD specifically on the Canis Major Dwarf: http://apod.nasa.gov/apod/ap071104.html . Perhaps the explanation there is more satisfying. Indeed, though, our APOD explanations are rarely perfect -- but we try. Thanks, kjardine, for point out that reference. - RJN

Hi Robert,

Thanks for the response! I'd have to say that the APOD explanation is even less satisfactory than the Wikipedia article as it gives no hint at all about the controversy over the existence of this object.

I do worry about that, as APOD captions are often cited as primary information by people who don't take the time (or don't have the time) to read the actual literature.

Do you ever add clarifications or corrections to these captions? If so, I'd be happy to send you a list of journal citations to look at.

rstevenson wrote:Wikipedia has a process for making these sorts of changes, if needed. Register and participate. It's a Good Thing.

If you check the discussion for that Wikipedia article, you'll see that I recommended that the article be deleted about two years ago. I was even supported by another poster who added another journal citation. Nothing has happened, however.

There is no way I'm going to delete the article myself. For a while I spent some time trying to repair various astronomy posts on Wikipedia, but I got tired of the weird politics and strange (to me) notion of truth often used to justify Wikipedia "facts". I've got better uses for my time than getting into a s**t fight on Wikipedia!

There was an APOD specifically on the Canis Major Dwarf: http://apod.nasa.gov/apod/ap071104.html . Perhaps the explanation there is more satisfying. Indeed, though, our APOD explanations are rarely perfect -- but we try. Thanks, kjardine, for point out that reference. - RJN

kjardine wrote:The Wikipedia article you cite has one paragraph remarking on this controversy - in my view this article should be rewritten to make it clearer that a "Canis Major Dwarf Galaxy" is a controversial hypothesis rather than a confirmed object, or still better, given the level of scientific controversy, it should just be deleted.

Wikipedia has a process for making these sorts of changes, if needed. Register and participate. It's a Good Thing.

Rob

There have been quite a number of articles published in the scientific literature questioning the existence of a Canis Major Dwarf Galaxy.

See:
http://adsabs.harvard.edu/abs/2008ApJ...672..930V

as just one example. (This article points out that the Orion Spur extends in this direction and is a more credible explanation for the observed "overdensity" than a dwarf galaxy.)

The Wikipedia article you cite has one paragraph remarking on this controversy - in my view this article should be rewritten to make it clearer that a "Canis Major Dwarf Galaxy" is a controversial hypothesis rather than a confirmed object, or still better, given the level of scientific controversy, it should just be deleted.

Chris Peterson wrote:

Michel P wrote:I wonder what the night sky would look like for a planet in M110 or M32. Would M31 be seen edge on, as a full disc or something in between? Would Andromeda block out a considerable part of the night sky, and how bright would it be? What insights on the structure and evolution of galaxies would be available from such a view that aren't accessible to astronomers on earth?

I think their night skies would look very similar to our own. From M110, M32 would probably resemble the Milky Way- a faint glowing band across the sky. From M32, M110 would probably resemble the Large Magellanic Cloud- one of our own satellite galaxies.

I don't think astronomers in those locations would see anything we couldn't see from here, in terms of understanding the nature of the cosmos.

From M32, M31 would probably be seen edge on and resemble "a faint glowing band across" one hemisphere of the sky almost perpendicular to it's own (relatively dust free) Milky Way.

From M110, M31 would probably resemble an enormously large Magellanic Cloud blocking out a considerable portion of one hemisphere of the night sky as regards to observing more distant galaxies.

We know little about the galaxies lurking behind our own Milky Way; even the close ones:

http://en.wikipedia.org/wiki/Canis_Major_Dwarf_Galaxy wrote:
<<The Canis Major Dwarf galaxy was first discovered in November 2003 by an international team of astronomers. Although closer to the Earth than the centre of the galaxy itself, the Canis Major Dwarf galaxy was difficult to detect as it is located behind the plane of the Milky Way, where concentrations of stars, gas and dust are densest. This, along with its small size, explains why it was not discovered sooner. The team of astronomers that discovered it were collaborating on analysis of data from the Two-Micron All Sky Survey (2MASS), a comprehensive survey of the sky in infrared light, which is not blocked by gas and dust as severely as visible light. Because of this technique, scientists were able to detect a very significant over-density of class M giant stars in a part of the sky occupied by the Canis Major constellation, along with several other related structures composed of this type of star, two of which form broad, faint arcs.>>

Michel P wrote:I wonder what the night sky would look like for a planet in M110 or M32. Would M31 be seen edge on, as a full disc or something in between? Would Andromeda block out a considerable part of the night sky, and how bright would it be? What insights on the structure and evolution of galaxies would be available from such a view that aren't accessible to astronomers on earth?

I think their night skies would look very similar to our own. From M110, M32 would probably resemble the Milky Way- a faint glowing band across the sky. From M32, M110 would probably resemble the Large Magellanic Cloud- one of our own satellite galaxies.

I don't think astronomers in those locations would see anything we couldn't see from here, in terms of understanding the nature of the cosmos.

Thanks RJN... The questions of Michel are nice too

I wonder what the night sky would look like for a planet in M110 or M32. Would M31 be seen edge on, as a full disc or something in between? Would Andromeda block out a considerable part of the night sky, and how bright would it be? What insights on the structure and evolution of galaxies would be available from such a view that aren't accessible to astronomers on earth?

I have emailed the WISE outreach team and asked them to check into these questions. I didn't write this APOD, and I haven't done much background research on this, but my guess would be that red blobs appearing in M31 itself are glowing dust in M31's dusty nebulas. The red dots scattered around the image, however, are more likely particularly cool stars that reside in our foreground Milky Way galaxy.

Well... if we forget about the dots for a moment...

What really intrigues me about this picture is the weird form the galaxy has in infrared. I see a ring of fire (which is really a huge spiral arm). Outside the ring, I see some matter that seems to be pulled away from the ring (left) and a partial outer ring (right). Inside the ring I see a smaller spiral system which is more like our own milkyway.

How did all this come to be?

is it possible that the better resolution we use on the heavens could help make points of EM radiation stand out? would these red points of light be missed in other resolutions?

not really sure how to word the question.

the analogy I am trying to use here is when you use binoculars in semi-darkness. all sources of light are magnified, not just the image.

I don't know, maybe this is coming out of left field.

At least one of the red dots corresponds to a fluffy white spot in visible light, so that would be a background galaxy, I guess.

I've compared the images. Most red dots appear as really faint gray dots in the visible light image.

If they were Bok-globules, as Art says, they should be within the milkyway, which seems a bit strange to me because they are so separated from everything. But maybe they are, I don't know.

Most of the infra- "red dots" are probably concentrations of Bok globules within H II regions:

http://antwrp.gsfc.nasa.gov/apod/ap091017.html
http://antwrp.gsfc.nasa.gov/apod/ap090414.html
http://apod.nasa.gov/apod/ap080215.html

http://en.wikipedia.org/wiki/H_II_region wrote:
<<The actual birth of stars within H II regions is hidden from us by the dense clouds of gas and dust which surround the nascent stars. It is only when the radiation pressure from a star drives away its 'cocoon' that it becomes visible. Before then, the dense regions which contain the new stars are often seen in silhouette against the rest of the ionised nebula—these dark patches are known as Bok globules, after astronomer Bart Bok, who proposed in the 1940s that they might be stellar birthplaces. Confirmation of Bok's hypothesis had to wait until 1990, when infrared observations finally penetrated the thick dust of Bok globules to reveal young stellar objects within. It is now thought that a typical Bok globule contains about 10 solar masses of material in a region about a light-year or so across, and that Bok globules most commonly result in the formation of double or multiple star systems.>>

what do we have if we compare the infrared to this picture? http://apod.nasa.gov/apod/ap100109.html do the red dots you see correspond to what looks like a galaxy?

Orin

I don't think they are astroids or dust... The red dots are all over the picture, so they are not associated with the galaxy. Maybe they are background galaxies or foreground stars.

So it's dust, then? You astronomers and your dust.

geckzilla wrote:Things which emit or reflect 22-micron light.

"Dust heated by Andromeda's young stars" to ~ 100ºK emits 22-micron light
(just as asteroids & comets heated by the sun ~ 200ºK emit 12-micron light).