From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Mon Apr 14 2003 - 13:44:02 PDT
On Sun, Apr 13, 2003 at 10:38:57AM -0700, Greg Aldering wrote:
> My conclusion from all this is that for z > 0.6 we have not measured
> extinctions for individual galaxies which are meaningful relative to
> the dmag ~ 0.25 size of the accelerating universe signal, as even with
> no intrinsic color dispersion eA_B > 0.25 for all z > 0.6 SNe in this
> sample.
I wouldn't immediately draw this conclusion. Each individual one by
itself, yes-- but there are four or five of them at z>0.7, and when you
divide by that sqrt(n), it does get down to be more comparable. What's
more, three of the four are from the new set, so there is an advance
there. (The disparity is greater if you include all at z>0.6.)
Most of our individual SN errors-- once you've added stretch and
magnitude errors to the intrinsic uncertainty-- even without E(B-V)
corrections from P99 weren't individually significant compared to the
accelerating/non-accelerating disparity, but in combination they were.
So, while your point is valid, I think it's more pessimistic about the
current data than we need be. Similarly:
> In the paper we can say we *have* measured the extinction well
> for 6 high redshift SNe, and that these measurements demonstrate for
> *individual SN host galaxies* the relatively low extinction measured
> *statistically* in P99 for an ensemble of high-redshift SNe. And
> moreover, 5 additional even higher redshift SNe as an ensemble also
> indicate small extinction for the observed SNe~Ia.
I don't think we need to say this. We don't need to apologize for our
error bars; quote them, and people can see them. Wherever the error
bars are, the cosmological limits *are* going to be quite a bit better
than what we had before, as the cosmology plots will show. I think we
should just show that, say the E(B-V)-correction limits are a lot
better, and leave it at that, rather than apologizing for the ones which
are worse.
Moreover, even if they aren't maybe as good as we'd want them to be, the
high-z E(B-V) limits *are* a substantial advance over the limits in the
same redshift range from P99. Previously, we had *no* SNe at z>0.6 with
dE(B-V)<0.1 (just measurment error, no intrinsic); the best was 97AP,
with dE(B-V)=0.13. Now we have five SNe at z>0.6 with dE(B-V)<0.1 at
z>0.6. We really have made an advance, and even if it's not "good
enough" I'd hate to undercut that advance in the text by suggesting that
only the lower-redshift E(B-V) measurements are worthy. There's no
dishonesty-- those errors are going into the cosmology with the E(B-V)
fits, and that cosmology would surely have had a smaller major axis had
they been better than they are.
(I still have to see how much all of that affects w; that's next, but
unfortunately I may not spit that out until tomorrow.)
-Rob
-- --Prof. Robert Knop Department of Physics & Astronomy, Vanderbilt University robert.a.knop@vanderbilt.edu
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