From: hyee@astro.utoronto.ca
Date: Fri Jan 26 2007 - 08:30:25 PST
Hi All:
I too echo that the proposal looks really nice, especially
with the impressive display of the results so far -- certainly
exceeded my expectation.
I agree with Anthony and others that we need to define N_gal
properly (both in the sense of defining whatever we actually
used in the proposal -which presumably must be treated as preliminary;
and later when doing science for real -- define how N_gal,
or other equivalent optical measurement to be used as a mass proxy).
I would say that I'm too pleasantly surprised at how good the plot
looks with a heterogeneous sample and that n_gal may not have been corrected
for all kinds of systematcis (counting aperture, absolute mag limit,
back ground correction etc)
>From: Piero Rosati <prosati@eso.org>
> 2)
> Mass-richness relation plot. It's nice, and the scatter/outliers not =20
> surprising given the nature of any richness parameter. We don't want =20
> to give the impression though this will be the kind of plots which =20
> will provide the "mass calibration" of future Xray/SZ surveys. Best =20
> mass indicators are currently physical quantities extracted from X-=20
> ray and SZ observations: T, Mgas, Lx,Y, Yx (the so called Yx=3DTx*Mgas =20=
>
> being the most fashionable these days). I doubt that anyone will use =20
> n_gal in the era of precision cosmology. This is mentioned at the end =20=
>
I would not quite be as pessimistic as Piero regarding using something
similar to N_gal for "precision cosmology". In fact, one of the
main goal for us in RCS is to use the lensing mass as a calibration
for richness as a mass proxy to do precision cosmology. The important
factor is not how accurate a mass proxy is, but knowing the dispersion
(see Gladders et al 2007 for the RCS1 results). Secondly, as it
stands today, there isn't really a practical way of getting Tx or
Mgas (or Lx, for that matter) for 20000 clusters, (though I guess
eventually there will be Y measurments of that order).
Howard
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