Hi Trevor,
Quote:
Originally Posted by Quark
There is still a problem, even with the Swin Mag article. Obviously it was not proof read by Duncan, or for that matter any of his team.
In the article the distance to SUCD1 is said to be similar to M 104, the distance is then given as 33,000 light years, obviously wrong and in need of another three zero's or 10 mega parsecs, obviously correct.
If you look at the published paper via the link in the previous post in this thread you will see the recessional velocity given for SUCD1 is 1293.1 +- 9.5 km/s. The recessional velocity for M 104 is 1024 +- 5 km/s, this gives a relative velocity for SUDC1 to M 104 of 269 +- 11 km/s.
Obviously from this data SUDC1 is not within M 104 but externally associated with it. There is also a couple of images in the original paper, of M 104 with SUCD1 highlighted to show its position relative to M 10
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I'm inclined to agree Trevor. Leinad posted the link to the original paper on arxiv.org and I took a look at that last night, well after my previous post about how bad the Fairfax snippet was compared to the Swinburne article. The upshot is, the Swinburne article got a few things wrong too. Further they haven't accurately encapsulated the tentative conclusion Duncan and the others have arrived at.
They find it difficult to conclude the origin of this object or even to classify it. It is very peculiar and (without re-reading the paper again and going on memory) (feel free to correct me -- anyone. That way we
all learn which is the object of the exercise) very compact object for its mass, probably in excess of 12gyr old (comparable to the globulars) has a composite spectrum about G-class (like many globulars) yet is from its half-light radius and overall brightness much, much bigger than any GC seen before. Its metallicity is very high or even extremely high for a GC -- comparable or even exceeding the most metal rich globulars. If it is a globular, where did all the metals come from?
The absolute magnitude is put at approx -12.3 -- comparable with many dwarf galaxies and somewhat higher than what is expected of even the brightest globulars. For comparison, that's about 2.3 magnitudes or 8-odd times brighter than the Milky Way's big-boys and even much brighter than say Mayall II (the most massive Andromeda GC). So it does not fit easily into the globular cluster bucket on that count either, but its position in relation to M104 well-out in the halo seems to fit well with being a GC and not a dwarf. It is a fairly bright (comparitively) X-ray emitter too whcih seems to fit with it being a GC. A great many if not nearly all the high mass globulars (eg 47 Tuc, NGC 2808, M15) are X-ray emitters for one reason or another.
So, it's size brightness etc is more consistent with it being a dwarf as is the metalicity. But ... there is no evidence of tidal tails -- which is what you'd expect if it were a tidally stripped dwarf -- even several Gyr down the track there would be a trail of stars and stuff trailing behind and preceding it in its orbit. So if it is the remnant core or a stripped dwarf, there's precious little evidence of it unless it happened a very, very long time ago. M104 seems to be a field galaxy -- almost alone in its surroundings. If this new object is a stripped dwarf, where did it come from? Dwarfs are rare if not unknown outside of populous galaxy clusters. If it's a dwarf, there is also little or no evidence of dark-matter which is also abnormal (though not unknown). If it is a dwarf, it is also the first to be detected in X-rays (very unusual).
So at present it fits rather badly in either category (G.C or tidally-stripped dwarf). Could it be a "missing-link" or a trasitional object between the two in an evolutionary chain? The paper talks of past simulations that ultimately produce things that look like and act like Omega Centauri out of a captured and stripped dwarf (Omega
may be a stripped dwarf) but apparently nothing as big as
this thing comes easily out of the simulations.
The way I read it, in the end they lean toward it being an exceptional, extremely massive metal-rich "super-globular" (my term-- not their's) that formed in association with M104 and isn't a captured dwarf, but it's a looooong way from certain.
One thing is for certain, this will be a highly-studied object over the next while and it looks fascinating.
I'd encourage anyone to have a read of the original paper -- for this sort of paper it's easy going (well-written) and most if not all people here will be able to digest the gist of it. Even if you read just the abstract and the conclusion, I think you'll learn a lot.
Thanks also to leinad for posting the link to the original paper. Thanks again to Robert for drawing everyone's attention to the report.
BTW, any of our ultra-deep imagers out there prepared to have a go at capturing this thing with an amateur 'scope ?? It is visible in the Sky-map.org image and even in the old POSS faintly. There are several stars near it about 17th/18th magnitude and it looks 18th magnitude--ish. Small but not too hard you'd think to image.
Best,
Les D