From: Chris Lidman (clidman@eso.org)
Date: Mon Mar 07 2005 - 15:38:48 PST
Hi Gabrielle,
Could you check that the version that is on the web is the
latest one. The latest version that I could find is
version 2.0 from Feb 21st.
Cheers, Chirs.
On Fri, 2005-03-04 at 14:09, Gabriele Garavini wrote:
> Dear Chris, Dear All,
>
> I've implemented the latest comments from Chris, Andy and Rob into a
> new draft of the paper and made some more modifications
> (supernovae.in2p3.fr/~garavini/papers)
>
>
> The most relevant news are:
>
> Section 3.3
>
> I've completely redone the statistics. I've included in the chi^2 test
> also the error on the x axis into. It was not there before. This was
> done propagating it into an y axis error according to the ew model of
> the low redshift SNe. This needed to be done for correctness, and has
> some nice consequences especially for MgII. Since the ew evolution of
> this feature has a big derivative wrt time the difference in the
> probability in table 5 is significant. Now the hypothesis that low and
> high redshift SN have the same ew trend is true for both Fe and Mg.
> Also, I've included in table 5 the same chi^2 test considering in the
> uncertainties also the systematic due to the misidentification of the
> fitting regions.
>
>
> Section 3.2.2
>
> The last paragraph about the systematic due to host galaxy removal was
> not exhaustive. I've expanded it explaining in some more details where
> the 10% of uncertainty comes from.
>
>
> Section 3.2.3
>
> In the second last paragraph of page 8 we commented on the higher
> than average values of ew for Mg before max light (a 2-sigma effect).
> The previous version of the paper included an explanation that did not
> convince neither me nor Chris. So I've done some thinking and some
> checks. Looking at the spectra and trying to identify the feature I
> noticed that in the early epochs since this feature is shallow it is
> easy to misidentify the maxima perhaps including some of the neighbor
> absorptions. This would bias the ew measurements toward higher values.
> This effect is taken into account by the misidentification systematic
> uncertainties. In the current version of this paragraph I explain that
> this could be the origin of the problem but that anyway it is not
> statistical significant.
>
>
> Section 3.2.1
>
> I included the latest comments from Rob. We now agreed on a description
> that hopefully will allow the reader to measure ew as was done for this
> paper.
>
>
> This should cover all the comment and worries raised so far.
>
> Please let me know what you think and how we proceed from here?
> I think now the paper can safely state that we do not see evolution.
> The new version includes all the authors that were included into the
> VLT paper. I know some of the affiliation are wrong. I'll check them
> out.
>
>
> Thank you very much
> Cheers
> Gabriele
>
>
>
> On Feb 23, 2005, at 4:48 PM, Chris Lidman wrote:
>
> > Hi Gabriele,
> > I've given some more thought about the possibility of doing a 2D KS
> > test with the data in figure 5. It seems to me that we cannot do
> > this test because one is not sampling the nearby and
> > distant samples randomly.
> >
> > The alternative is the chi-sq test, as you have done. The
> > resulting probability (0.15) is low. The question we must now ask
> > ourselves is do we believe this result. If we do, then we cannot
> > say that there is no evidence for evolution, as we do in the abstract.
> >
> > There could be reasons for the difference. The example you give
> > is systematic errors in host galaxy subtraction. If this is the case,
> > why would if affect the the Mg II index but not the FeII index.
> >
> > Regards, Chris.
> >
> > On Tue, 2005-02-22 at 20:56, Chris Lidman wrote:
> >> Hi Gabriele,
> >> Thanks for the reply. I forwarded your paper to Andy and he has
> >> provided some additional comments. Andy's comments consist of
> >> grammatical corrections, which I reproduce below, and an important
> >> question regarding host galaxy subtraction.
> >>
> >> Before I list Andy's comments, I'd like to add to my point
> >> concerning
> >> the significance of the difference seen in figure 5.
> >>
> >> The test you have done is to test whether high redshift SNe are more
> >> similar to low redshift normal SNe or to low redshift underluminous
> >> SNe.
> >> You have found the former to be true. However, this does not mean that
> >> they are the same as low redshift normal supernova. Hence, you cannot
> >> conclude that there is no evolution. For this, you need to conduct a
> >> more sophisticated test.
> >>
> >> It may not be easy to do this in 2 dimensions. In 1D, the
> >> obvious tests would be the KS test and Student's t-test.
> >> However, using a web search, I found the following web page
> >> which describes a 2D KS test.
> >>
> >> http://beowulf.lcs.mit.edu/18.337-2002/projects-2002/ianchan/KS2D/
> >> Project%20Page.html
> >>
> >> Have a look and let me know what you think.
> >>
> >> In addition to Andy's comment regarding host galaxy subtraction, one
> >> should note that the bias could go either way. In some cases, you
> >> might
> >> subtract too much host and in other cases you might subtract too
> >> little.
> >> Currently, the paper assumes that the error in the subtraction is 10%.
> >> Where does this percentage come from? I think that this needs more
> >> justification.
> >>
> >> Cheers, Chris.
> >>
> >> Start of Andy's comments
> >> ========================
> >>
> >> Comment #1
> >>
> >> The largest source of uncertainty is the host galaxy subtraction. Yet
> >> this is swept under the rug. If this was done using the determination
> >> from my program, for example, you can't trust any of the conclusions
> >> from the paper. My program simultaneously fits host galaxy and SN
> >> templates. In other words, it *assumes* that the high-z spectra is
> >> similar to a low-z one and subtracts an amount of host light such that
> >> the high-z and low-z spectra will look similar. The proper thing to
> >> do
> >> would be to use the photometry (e.g. percent increase) to constrain
> >> the
> >> amount of host galaxy light, and to use imaging and spectral features
> >> to
> >> constrain the host characteristics. You might be able to say some
> >> spectrum has 30% host +/- 10%, and is either an E, SO, or Sa. Then
> >> you
> >> could do different subtractions in that parameter space and test the
> >> results. Defining a technique like this would be a great addition to
> >> this paper because any time people use high-z spectra they are going
> >> to
> >> have to do something like this.
> >>
> >> Comment #2
> >> ==========
> >>
> >> One other point -- in the SNLS we have many 91T/99aa SNe at high
> >> redshift. So there is no need to make a big deal out of having one in
> >> the sample, as this paper does.
> >>
> >> Minor comments
> >> ==============
> >>
> >> p. 1
> >> Intro, par. 1 -- plural of supernova is supernovae
> >> tidly ????
> >> par. 4 it should be pointed out that the effect metallicity has
> >> on the spectrum pointed out by Hoeflich and Lentz are only for
> >> early-time
> >> spectra, of which there aren't many here.
> >>
> >> par. 6 -- I have submitted a paper on SNLS gemini spectra -- Howell et
> >> al.
> >> 2005, ApJ, submitted
> >>
> >> p. 2, section 2.1 last sentence, One SNe -> One supernova
> >>
> >> last paragraph of section -- two days is no longer the uncertainty for
> >> the
> >> spectroscopic epoch determination in Hook et al.
> >>
> >> section 2.3, par 1 -- you say EWS but it is not defined yet.
> >>
> >> p. 4
> >> table 2 'Si' should be 'Si 4000' since you say it is absent in
> >> underluminous SNe.
> >>
> >> first paragraph on page - there is a period missing before SN 2002fd
> >>
> >> p. 5
> >> 3.1, 3rd par. "uncertainty in the redshifts is taken to be 300 km/s if
> >> the
> >> redshift was estimated from galaxy lines..."
> >> shouldn't this be proportional to the redshift?
> >>
> >> 3.2 first sentence -- delete ", they" and second comma.
> >>
> >> p. 6
> >> "possible involved" delete involved
> >>
> >> p. 7 last par in 3.2.1 delete space in "spectra ,"
> >>
> >> 3.2.3, 4th par -- delete space: "( with"
> >>
> >> p. 8 3.3 miss-identification -> misidentification
> >> this whole parenthetical expression should be made into a new sentence
> >> because it is confusing with "uncertainties" written twice in a row.
> >>
> >>
> >>
> >> On Tue, 2005-02-22 at 05:24, Gabriele Garavini wrote:
> >>> I'm very sorry chris I sent by mistake the wrong file.
> >>> Here is the one I meant to send.
> >>> Thanks
> >>> Gabriele
> >>>
> >>> On Mon, 21 Feb 2005, Chris Lidman wrote:
> >>>
> >>>> Hi Gabriele,
> >>>> Could you resend the attachment. The one I received seems to be
> >>>> chopped at the end.
> >>>>
> >>>> Regards,
> >>>>
> >>>> Chris.
> >>>>
> >>>> On Mon, 2005-02-21 at 13:29, Gabriele Garavini wrote:
> >>>>> Dear Chris
> >>>>>
> >>>>> thanks you very much for the careful reading of the paper. I've
> >>>>> implements most of you comments. Please find all my answers in the
> >>>>> attached file. I also changed extensively the section about EW
> >>>>> (3.2) I
> >>>>> hope this will allow us to go to submission shortly.
> >>>>>
> >>>>> Thanks again
> >>>>> Hasta la vista.
> >>>>> Cheers
> >>>>> Gabriele
> >>>>
> >>>>
> >>>>
> >>
> >>
> >
> >
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