From: Nino Panagia (panagia@stsci.edu)
Date: Tue Jan 24 2006 - 13:06:49 PST
Della Valle et al (2005, ApJ 629, 750; see also Della Valle & Panagia, 2003,
ApJ 587, L71) have demonstrated that SNIa rates per unit mass (see Mannucci
et al 2005, A&A 433, 807) are about a factor of 4 higher in radio-active
ellipticals than in radio-quiet ones, AND argued that the radio activity is
likely to be triggered/caused by galaxy captures and/or interactions. Note
that in this scenario, different channels should be operating to produce the
"excess" of SNIa in radio galaxies because very short timescales (about
100Myr) are associated with intense radio activity in ellipticals (see
Mannucci, Della Valle & Panagia, 2005, MNRAS, submitted, and
astro-ph/0510315).
From this it follows that the rate of SNIa explosions in cluster
ellipticals are expected to be higher than in field ellipticals because the
frequency of interactions with other galaxies is higher.
Second order effects may affect this "prediction" IF dwarf galaxy capture
(rather than tidal interactions) is the main mechanism for enhancing SNIa
rates AND radio emission, most of the available dwarf galaxies may be
captured at early times and very few be left for late time "consumption".
From all of this I would argue that cluster elliticals are DIFFERENT from
field ellipticals in their SNIa rates and, therefore, comparing SNIa rates
from the SAME galaxy types in DIFFERENT environments is very valuable to
understand and clarify the origin and properties of SNIa AT ALL redshifts.
Ciao - Nino
----- Original Message -----
From: "Greg Aldering" <aldering@panisse.lbl.gov>
To: <HSTclusterSN@lbl.gov>
Cc: <galdering@lbl.gov>
Sent: Tuesday, January 24, 2006 3:16 PM
Subject: uniqueness of cluster ellipticals
>
> 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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