From: Isobel Hook (imh@astro.ox.ac.uk)
Date: Fri Feb 28 2003 - 09:45:30 PST
Hi Rob et al.,
I've gone through the P99 discussion of systematics and here's what was
covered. Below I have tried to say what I think needs doing for the HST
paper in each of these sections (with suggested people to do them!).
However as you will see, in some cases I don't know enough of the details
to assess this properly.
Cheers,
Isobel
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P99 Section 4 - systematics
4.1 Extragalactic extinction
- thouroughly covered in HST paper
4.2 Malmquist bias
- What matters is the difference in Malmquist bias between low and
high-z sets. HST paper uses new data for both low- and high-z SNe.
High-z: P99 estimated size of effect by considering completeness
and associating this with SN number counts as a fn of mag
(actually it's not clear how this was done!). Also took into
account non-perfect correlation between discovery mag and peak
mag.
Low-z: P99 assumed similar effect but correlation between peak and
discovery mags is stronger than for high-z set.
- For HST paper, include new comparison of stretch distributions as
in P99.
To estimate size of malmquist bias effect:
- Calculate correlation between peak and discovery mag for HST set.
[Reynald/Rob?]
- use same assumed underlying SN N(m) as P99???
Otherwise need new assesment of selection bias for
high-z set [Reynald/Greg?]
- use same assumptions for low-z set as P99
(how much do we know about the R99 selection method?)
4.3 Gravitational Lensing
- can proabably use same arguments as P99, i.e. deamplification
bias <1% at the redshift of our SNe. (how strongly does the
deamplification bias depend on redshift of the SNe?) [Greg]
- Could re-calculate fits for partially-filled beam cosmology as in
P99 [who did this last time?]
4.4 SN evolution
- Spectra consistent at low & high-z (same argument as P99)
- lightcurve rise-time & shape similar (same argument as P99 but
update based on Gerson's paper) > constraint on changes in
width-luminosity relation. [Gerson/Peter/Greg?]
- Small evolutionary effects on rest-frame U-band (cf Hofflich's
paper) could affect colour & k-correction. P99 argument needs
updating since more of the HST data sample the
U-band. [Greg/Rob/Peter?]
- Mention constraints from Sullivan paper: constraints on variation
of width-luminosity relation with environment [Mark?]
4.5 Further checks
- Sensitivity to width-luminosity relation: Could redo fit without
using stretch correction? (fit D in P99) or at least show
stretch distribution and argue that it is peaked around s=1. [Rob]
- sensitivity to non-Ia contamination: This is already covered? Could
also repeat fit throwing out all but the absolutely certain ones
[Andy/Rob].
- sensitivity to galactic extinction model: P99 re-did fits using
Burstein & Heiles extinction model. Not necessary now? (or just
re-quote numbers from P99?)
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