From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Fri May 23 2003 - 06:48:45 PDT
On Thu, May 22, 2003 at 06:20:20PM -0700, Greg Aldering wrote:
> I also added a too-faint cut, requiring that SN not be fainter than N
> times its magnitude uncertainty (including an intrinsic error of
> 0.17). In Rob's last fits, all the residuals were within 3-sigma for
> the low-extinction subset, even though no cut on deviation was
> applied.
In fact, there was one that was too faint -- 9733, which got thrown out
from the main set. It's a 6-sigma outlier to the faint side from the
primary (non-extinction-corrected) fit.
> Thus, my cut considers the likelihood that if there were a
> significantly dim outlier we might have chosed to reject it even
> without a well-measured color to prove that it is reddened.
...so, in this case, we may well have, although we don't have the data
to show that 9733 is faint just because it's reddened.
> I find that our method does have a bias, but that the bias is small
> compared to our other systematics. However, it might not be small
> relative to the Riess prior (that has to be checked).
The bias with the Riess prior is complicated, of course, since colors
which are divergent simply because of measurement errors get modified.
This bias tends to operate in the *other* direction from the lowe bias,
assuming that the high-redshift supernoave have worse E(B-V) error bars
than do the low-redshift supernoave (i.e. high-redshift supernovae get
made brighter on the average, since all negative E(B-V) values get
suppressed to zero but positive E(B-V) values are still allowed to be
corrected for, albeit at a reduced level).
> Here is what I get:
>
> N-sigma <A_B> <A_B> Bias
> dim cut low-z high-z low-high
> -------------------------------------
> 2.0 0.068 0.081 0.013
> 2.5 0.075 0.094 0.019
> 3.0 0.080 0.104 0.024
Was this using the distribution E(B-V) error bars from the full
high-redshift set?
-Rob
-- --Prof. Robert Knop Department of Physics & Astronomy, Vanderbilt University robert.a.knop@vanderbilt.edu
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