From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Sun May 18 2003 - 11:04:03 PDT
On Sun, May 18, 2003 at 12:47:16PM -0500, Robert A. Knop Jr. wrote:
> > Given that, we have to reconsider what purpose the low-extinction subset
> > serves. We are using it because models tell us that there should be
> > a ridgeline of low-extinction. Therefore, we a supposing that as long
> > as we throw out extincted SNe, nature is guarenteeing similarity in
> > whatever small residual amount of extinction that remains. We have
> > tested whether this assumption holds for the low-extinction subset,
> > and we find that within our ability to measure, it does hold.
>
> Unless we want to put in some sort of prior assumption on the intrinsic
> extinction distribution for purposes of evaluating the systematic, then
> we can't do any better than that uncertainty of 0.015 or 0.025
> magnitudes-- which is going to give us something like an 0.1 systematic
> uncertainty in the flat-universe value of Omega_M on the low-extinction
> subset. I'd like to avoid putting in a prior assumption, after we spend
> all that time in the paper trying to discourage that sort of thing when
> doing statistical E(B-V) corrections.
OK, thinking about this more--
Of course, as has been previously noted, we *are* using a prior on our
low-extinction subset, that is E(B-V)=0+-0. This prior has the
advantage of being unbiased even if your error bars are different at low
and high redshift. (Sort of; in fact, there is an implicit bias,
because if one set has worse error bars, it will keep more mildly
extincted supernove than the other set. The prior doesn't *impose* a
bias the way the Riess one does)
If we really want to be self-consistent and run with this-- basically
doing what you say, we've tested this assumption and it sure seems to
hold-- then we should use *no* host galaxy extinction systematic
whatsoever on the low-extinction subset. If somebody cares about
extinction, then they look at Fit 6.
This approach may actually make the most sense.
Thoughts?
-Rob
-- --Prof. Robert Knop Department of Physics & Astronomy, Vanderbilt University robert.a.knop@vanderbilt.edu
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