From: Serena Nobili (serena@lpnhep.in2p3.fr)
Date: Mon Jan 10 2005 - 07:30:07 PST
Dear all,
here is the referee's report on the Iband paper. It sounds quite tough at
the beginning, but it is not that terrible after all. One major point is
on 1999Q. He seems to want us to state clearly how much is our magnitude
of the SOFI point. I certainly need a quick feedback on this comment, while
I work on the rest.
Thank you in advance for you help.
Cheers,
Serena
---------- Forwarded message ----------
Date: Fri, 07 Jan 2005 19:57:34 +0100
From: aanda.paris@obspm.fr
To: serena@lpnhep.in2p3.fr
Subject: AA/2004/2463
07/01/2005
Dr Serena Nobili
Our Ref. : AA/2004/2463
Dear Dr Nobili,
Your paper "Restframe I-band Hubble diagram for type Ia supernovae up to z sim~0.5" was submitted to a competent referee who recommended publication after substantial revision (see enclosed report).
Please take all of the referee's comments and suggestions into account in revising your work and send us the new version (in referee format) at your earliest convenience. Instructions for resubmission can be found at address https://mms-aanda.obspm.fr/is/aa. Your author ID number is 13552.
In your cover letter, please indicate precisely all the changes made in the revised version, and mark them clearly (e.g., using boldface) in your manuscript.
With best regards,
Francoise Combes
A&A Editor
-----------------------------
Referee Report
The use of Type Ia Supernovae for cosmology has produced remarkable
results. The checking of these results is of utmost importance and the
paper 'Restframe I-band Hubble diagram for type Ia supernovae up to z
sim~0.5' by Nobili et al. is trying to present such a check.
The paper has two main topics: The necessary establishment of the
I-band light curves of Type Ia Supernovae and the construction of an
I-band Hubble diagram. The former is a precondition for the latter. The
paper has to remain exploratory, since there are not enough data to
populate the Hubble diagram at redshifts z>0.3 where the cosmological
effects start to become significant.
There are several shortcomings with this paper and it should be modified
considerably before it can be recommended for publication. However,
the paper can be brought to a stage where it can be published with some
effort.
The light curve fitting is rather ad hoc. The motivation to use B-band
light curves to construct a surrogate I-band light curve is not
explained anywhere. The authors should give a reason, why they chose
this route and not another. There are obvious shortcomings from this
approach that are not described in the paper. E.g. the late decline of
the I band, which is typically faster than in B can not be described
with this method at all. This means that after about 40 days past
maximum, the I light curves can not be fit any longer. The paper does
not use these late-phase data, but it should be made clear that the
proposed model can only fit the maximum phase. By the way, the approach
by Contardo et al. allowed them to fit the light curves, within the
stated limitations, over a much longer time than what is proposed here.
Another issue are the rise times. The paper states that it is 'assumed
that the rising part of the light curve in I-band is the same as in
B-band' to then on the next page say 'the trend in the residuals' in the
fit to SN 1994D 'shows the limitations of the model.' An inspection of
Figure 1 shows that this is evident in all cases where data in the rise
is available. In all cases the fit has strong systematic deviations,
when the peak is defined through pre- and post-maximum data. SN 1994D is
just the case in point. It seems important to make the paper consistent
in this respect.
The above draws the result of Figure 2 into question. This figure is
remarkably different from what was found in Contardo et al. (their
Figure 4). This discrepancy should be discussed in the paper.
Another example is the exclusion of two (SNe 1997br and
1998ab; both 'spectroscopically peculiar') supernovae due to the Monte
Carlo fits. They happen to be the two with the smallest ratios between
peak and dip in the light curves. The fact that the Monte Carlo fits
fail to reproduce these light curves consistently is probably an
indication that the model fails here as well.
Table 2 should list the number of data points used in the fit. This
would help the reader to assess the goodness of the fit as well.
Especially, since these light curves are then later used to fit the
distant supernovae, it would be good to restrict the construction of
light curve 'templates' to only objects that have an over-constrained
fit, i.e. more than let's say 10 phases spread over at least over the
two peaks. Establishing a template with 6 data points appears unreliable
given the model.
Light curves are stretched according to values derived from the B light
curves. What would be the rationale to apply the same stretch in I as
well?
The fits are done in flux units. Does that mean the magnitudes are
converted into flux, fit and then converted back into magnitudes? Why is
this done like this? How are the errors treated? This is an important
detail that needs to be explained.
The authors should decide what they want to do with SN 1999Q. As it is
right now, they introduce the data for this supernova to quickly reject
them as non-consistent. That would be OK, if they then would refrain
from presenting all the analyses as with the other two objects. I
suggest to either accept the published (Riess et al.) data as they are
or, if the data can not be used, reject them and leave it at that. It
does not make sense to fit a light curve, calculate a brightness and put
the point into the Hubble diagram, if the data can not be trusted. The
authors should indicate, why the data can not be trusted. Just saying 'a
re-analysis of the publicly available SofI data suggest that the
published J-band magnitude may be too faint' is not good enough. The
public data contain all the information necessary to derive a reliable
value. If it differs from the published result the difference should be
stated explicitly.
In several places the paper is confusing in the way it presents the
samples. The abstract quotes 26 local supernovae, but the reader is
confronted with different numbers (42, 28) in the text. It might be useful
to state the sample selection (redshift range and exclusion of
spectroscopically peculiar supernovae) in the abstract so that this is
clear from the beginning. Maybe the selection criteria could be
summarised again at the beginning of section 3.
The use of references is sometimes unclear and appears also occasionally
arbitrary. It would be good to carefully go through the paper again and
sort these out. Suggestions are made below as well.
Specific comments:
1. 'spectroscopic peculiar' should be changed to 'spectroscopically
peculiar' throughout the text.
2. add Schmidt et al. (1998) to the reference list to the first sentence
in the introduction.
3. add '(similar to Riess et al. 2000)' as a reference to the first
sentence of the last paragraph of section 1.
4. The references for SN 1991T (section 2.2) are rather strange. It
appears as if there is a mix-up with the following sentence. The
references for SN 1991T should be Filippenko et al. 1991, Ruiz-Lapuente
et al. 1991 and Phillips et al. 1992. The references for Li et al. 2001,
Howell 2001 and Garavini et al. 2004 presumably refer to SNe 1995bd,
1997br, etc.
The sentence starting with 'However, not all of these show ...' is
unclear. Which supernovae are meant with 'these'? SN 1986G, SN 1993H or
others?
5. In one paragraph Type Ia Supernovae are called 'standard candles' and
the next (only two lines down) they are described to show 'a variety of
properties.' It is passages like these that confuse the reader.
6. What does 'somewhat deviant' mean (caption of figure 6)? This
statement should be quantified.
7. There is a change from observed redshift to a redshift corrected to
the CMB frame between Tables 2 and 3. This should be explicitly stated
either in the text or the captions to Table 3.
8. Table 4 and its discussion in the text are meaningless. Since the
fits in the Hubble diagram is done with all data sets the smallest
sample one will have the least weight and hence largest uncertainty.
With the larger uncertainty the 'offset' automatically can be larger.
Not surprisingly, all samples are consistent with each other within the
errors. This table and the corresponding section should be dropped.
9. The first sentence of the third paragraph in section 5 should start
with 'The low statistics of the high redshifts sample is insufficient
...' No statement can be made whether the concordance model is favoured
or not from the presented data.
10. In the same paragraph there is a garbled sentence, the meaning of
which did not become clear. However, as suggested above the discussion
of SN 1999Q should be dropped here anyway.
11. It appears from the fits that a dust model with R_V=9.5 is the most
favoured case, given the data. For the Monte Carlo simulation to check
for the sample size to reject a dust hypothesis the number of individual
data points per individual supernova must be important as well. This
should be described.
12. The fourth paragraph of section 8 should start: 'J-band measurements
of one high-redshift supernova plus published data of one more were used
to extend ...'
Also, instead of saying 'seemingly inconsistent information' on SN 1999Q
the authors should be more explicit. It is alright to say that the authors do
not trust the data and hence discarded this object.
13. There is an interesting mismatch in the interpretation between
concordance model and the analysis of potential dust in the conclusions.
The 'concordance model ... is found in better agreement with the data
than other models' but the dust analysis yielded 'no firm limits on the
presence of grey dust.'
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