From: Chris Lidman (clidman@eso.org)
Date: Tue Feb 22 2005 - 15:56:09 PST
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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