From: Greg Aldering (aldering@panisse.lbl.gov)
Date: Sat Apr 12 2003 - 23:03:51 PDT
>> If so, then I would advocate letting the scatter of our own
>> U-contaminated SNe tell us what intrinsic dispersion to use for the
>> final Hubble-diagram points.
>
>There's not nearly enough information to do that. We only have a few
>supernovae at high enough redshifts that the U really contributes, and
>there aren't nearly enough to do a sort of ridgeline analysis to get an
>idea of an intrinsic color just from them. Any scatter could be a
>scatter in the reddining too. The problem loops back upon itself
>because you use the intrinsic color to get the host galaxy extinction,
>but you'd need that host galaxy extinction in order to estimate anything
>about the intrinsic colors. (With low-redshift supernovae studied in
>multiple bands, you can use the other colors to constrain extinction
>befor etalking about U-band.)
Sorry if I was unclear -- I meant that we could use the magnitude
dispersion about the Hubble line for those few high-redshift SNe, after
they are extinction corrected using whatever extinction determination
you choose. This simply addresses whether the assigned magnitude
uncertainty is appropriate. After extinction correction, the color
error dominates the magnitude error, so scaling the color error up or
down to get chi-square/DOF ~ 1 gives an estimate of the correct color
error to use.
I realize there are few points to do this with; in Table 3 the 5
highest redshift SNe have large quoted errors in E(B-V), which I assume
has something to do with the assigned intrinsic uncertainty in U-B at
max. If that is true, then you can use the approach I suggest to
estimate the U-B color dispersion to within a factor of 2. Depending on
the value, we might then have a better reason to choose 0.04 or 0.09
from Peter's fits to Jha's data.
Since this is very simple, it is at least worth finding out what can
be learned from this approach. I would do this myself if I had the
residuals for your extinction-corrected OM-OL fit, and knew what intrinsic
color uncertainty had been assigned to each SN.
Since your cosmology fits (I did find the attachment after you pointed
it out) show that the assigned U-B color dispersion is not all that
important for OM-OL, I think the main remaining question then is whether
or not we think we have good extinction measurements for those 5
highest-redshift SNe. (There may also be a question of the role the
assigned color uncertainty plays in the OM-w plots.)
Cheers,
Greg
- Greg
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