Finally work!
Today no paper work!Spent the whole day preparing the observation that starts monday at the INT in La Palma ... wishing for clear sky!
posted by Cris Da Rocha @ 10:44 PM
Friday, November 25, 2005
Spent the whole day preparing the observation that starts monday at the INT in La Palma ... wishing for clear sky!
A daily summary of my science work (and probably other activities of my life - life itself, my family, Brazil, Germany, cycling, music ...). Why coffee? Because I like it and it's directly related to science (at least in Astrophysics) :-))
Previous Posts
- Lots of paperwork!
- Paperwork "Do It" day!
- One "Do it!" day!
- Yet another late post ...
- Thinking day
- Reprocessing
- Late post from yesterday :-)
- Journal Club really starts
- Processing the whole pack!
- Flatfields 4
5 Comments:
Cris, You asked me about intracluster light. The reason I do not think it is stripped out of the galaxies in the clusters is two-fold:
1. E and S0 galaxies in clusters look identical in all respects (sizes, concentrations, central densities, etc) to E and S0 galaxies in the field; they do not look like they have undergone any special transformations.
2. Quantitatively, if you estimate the tidal radii of cluster galaxies, you will find that their stellar sizes are much smaller than their tidal radii. This is in contrast, eg, to MW GC Pal 5, which is clearly tidally limited: Its stars extend to the tidal radius, and there are apparent tidal streams of stars being removed just as expected.
If I had to add a third point, I would add the comment that we don't see tidal streams in clusters, to my knowledge; so we don't see any evidence for past tidal activity, and we don't see any evidence for present tidal activity.
Three interesting points.
But about the question of signs of interaction. There are some papers, I recall Gregg and West, 1998 and Trentham and Mobasher, 1998, where they find (independently) signs of tidal structures being dissolved in Virgo.
But, in case it is not stripped material, the diffuse component that can be seen would have formed there?
Yes, some recently added galaxies to Virgo do appear to be undergoing tidal distress, but I think that doesn't contradict what I wrote above, for most galaxies.
Since I posted, Beth Willman (NYU) pointed out to me that it could be that though the galaxies are not tidally limited now, they might have been in the past, when they were resident in smaller, more compact halos, so the ICL could still be tidally stripped material.
My presumption is that the ICL is partly stuff formed in situ and partly stuff liberated when galaxies get "eaten" by the cD. Of course, with only minor abuse of the English language, you could call that "tidal stripping".
David,
the question comes from the fact that star formation out side of galaxies has being discussed the last years but some don't believe it.
Since in compact groups the galaxy interactions are quite intense, we really believe the IGL comes from stripping and, of course, make some assumptions based on that fact.
If the stars are formed on the IGM without any "relation" with the galaxies then such assumptions would have to be reformulated.
Cris,
That's a good point. If most galaxies falling into clusters have gone through a compact-group phase (which might not be unreasonable since so many of the galaxies in clusters are early-type), then they may bring in quite a bit of ICL as they fall in.
The only thing I can say is that there doesn't appear to be a lot of stripping going on in clusters after the galaxies fall in.
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