One of the many, many wonderful things about the Virgo Cluster is that it lies behind a great big hole in Galactic dust. So we can measure the galaxies there without worrying too much that the foreground dust has made them appear significantly redder and fainter than they really are*. That's especially nice for me, because I can't stand dust. I just cannot bring myself to get interested in it. Sure, it may be an important component of star formation, but... come on, it's dust. Don't expect an insightful commentary, is what I'm saying.
* This is called extinction, presumably just to be confusing.
Anyway, through some very sophisticated modelling it is possible to correct for the reddening due to foreground dust. Once that was done, the authors looked at the extinction variation of Virgo galaxies that must be caused by extragalactic sources. Normally I'd probably be skeptical, but the trend is so darn clear - more reddening near the cluster centre with a very rapid drop off with radius - that
it looks to be pretty convincing, at least to a naive dust-aversion person like me.
They're even able to make a map of the extinction, albeit at low resolution, but you can clearly see something. Dunno what it is, but it's definitely there (the issue is you can only measure the dust by looking at galaxies which have been reddened by it, rather than detecting it directly). Broadly, they say it seems to follow the same distribution of the intracluster light, thought to result from stars that have been thrown out of their galaxies by tidal interactions. They estimate the total mass of dust at just 3 billion solar masses, which is about the same as the gas mass of a single large dwarf galaxy. Being able to detect this when spread over such an enormous area is pretty darn impressive.
The main thing I wonder about is survival. They say the expected lifetime for dust in the cluster environment is about 100 million years, which is not all that long. Are there likely to be enough tidal encounters pulling out sufficient dust to explain the observations ? There's not that much of it, but I would expect it to be pretty hard to remove since it should be mainly found in the inner regions of galaxies. I dunno. I might just be too naive on this, but it would certainly be interesting to know how much dust can be removed in an encounter and then get a handle on how often such encounters must occur. Which would likely end up as an exhausting project involving all kinds of ghastly physics with a result that may or may not be interesting to anyone. Such is life.
The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) VIII. Diffuse dust in the Virgo intra-cluster space
We present the first detection of diffuse dust in the intra-cluster medium of the Virgo cluster out to $\sim$0.4 virial radii, and study the radial variation of its properties on a radial scale of the virial radius.
No comments:
Post a Comment