From: Marc Postman (postman@stsci.edu)
Date: Tue Jan 24 2006 - 12:36:53 PST
Yes Saul and I discussed this today as well. One answer (in our favor)
would draw upon the recent work from the UDF/GRAPES survey (Pasquali et
al 2006, ApJ, 636, 115). In this work, they find that: "Blue clumps
have been detected in nearly 50% of the z ~ 1 early-type galaxies;
their photometry is suggestive of young star clusters or dwarf
irregulars if they are assumed to be at the
same redshift as their host galaxies. We speculate that these clumps
may represent recent accretion episodes and that they
could be a way to produce blue cores if their dynamical time is such
for them to rapidly sink to the galaxy center."
Such clumps undoubtedly are dusty as well (they note this in the
paper). So there is clear evidence coming now that field ellipticals at
high-z are not dust-free - or at least not completely devoid of some
on-going star formation. The ellipticals in clusters at z ~ 1 to date
have not shown such blue clumps. Coupled with the homogeneity of the
CMR data, I think we can probably add some words to the above effect.
What do ya think?
Marc
On Jan 24, 2006, at 3:16 PM, Greg Aldering wrote:
>
> This is a question for Marc, Mike, Peter, Adam, etc.
>
> In reading over the current draft of the HST proposal and discussing it
> with Saul, it seemed that we are missing a strong counterargument to a
> possible claim that SNe in field ellipticals are just as useful as
> those found in cluster ellipticals. Right now, the best we are able
> to do is point out that by the end of this Cycle our elliptical galaxy
> sample will match what has been published from the searches of the
> GOODS
> fields. But, we don't address whether cluster elliptical hosts are any
> better or worse than field elliptical hosts.
>
> Presumably any such an argument would have to center around differences
> in the dust content or likelihood of star formation in field versus
> cluster ellipticals. The argument might also revolve around testing SN
> evolution more cleanly in clusters since the formation epoch of cluster
> ellipticals might be more secure. Is there a strong argument along
> these lines that can be made for ellipticals at z ~ 1? Are the cluster
> ellipticals going to be older or less dusty?
>
> I could believe that a deep spectrum of a field elliptical SN host
> would provide the desired constraints on the amount of star formation
> or the age of the stellar population. If this were done for the
> existing GOODS field elliptical hosts, perhaps some SNe would become
> suspect, but perhaps they would not. So, I am worried that there isn't
> a strong claim distinguishing cluster and field ellipticals that can't
> easily be undercut.
>
> Any ideas?
>
> Greg
>
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Marc Postman Email: postman@stsci.edu
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