From: Lori Lubin (lubin@physics.ucdavis.edu)
Date: Tue Jan 24 2006 - 13:00:54 PST
Hi Marc,
That is very interesting. It should be noted (though probably not in
this proposal) that about 60% of the spectroscopically-confirmed
red-sequence galaxies in the ACS field of CL1604+4304 at z = 0.9 show
detectable [OII] emission in our DEIMOS spectra. This suggests at
least some star formation in the cluster early-types at these
redshifts. it is important to get high S/N and high-spectral-resolution
spectroscopy to quantify this accurately.
Cheers,
Lori
On Jan 24, 2006, at 12:36 PM, Marc Postman wrote:
> 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
>>
> -----------------------------------------------------------------
> Marc Postman Email: postman@stsci.edu
> STScI - CMO Phone: +1-410-338-4340
> 3700 San Martin Drive Fax: +1-410-338-4424
> Baltimore, MD 21218 U.S.A. http://www.stsci.edu/~postman
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