Starship Asterisk*

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.

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

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

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

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

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!

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