snls : spectroscopy of supernovae with the vlt (status) grégory sainton lpnhe, cnrs/in2p3...

SNLS : Spectroscopy of Supernovae with the VLT

(status)

Grégory Sainton LPNHE, CNRS/in2p3

University Paris VI & VII

Paris, France

On behalf of the SNLS collaboration

Moriond 2004 : Exploring the UniverseG. Sainton : SNLS, SN identification with VLT

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Contents

Overview of the VLT observations

Spectroscopy analysis

First (preliminary) results


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Overview of the VLT observations


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SNLS observations with the VLT

• 240 hours for 2 years (VLT large programme) on FORS-1 (longslit spectrograph) to identify SNe of the CFHTLS SN programme.

• Target of opportunity mode :– No precise observation date provided in advance.– Observations are submitted, as soon as a

candidate is discovered at CFHT.– Our observations have first priority and are

conducted in Service Mode.


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Observing at VLT


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Data processing

• Data available in Garching about 12 hours after the observations.

• Preprocessing of the data done with the FORS pipeline, customized for the SNLS use.

• Extraction of the spectra performed with our own tools, based on a minimum variance estimation (Horne, 1986).

•It produces the spectrum and its associated error.

•The host spectrum is extracted when possible.


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Spectroscopy analysis


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Two goals for the spectroscopy :– Identify the SN

(Ia, or non Ia).

– Measure of the redshift.(host galaxy lines or from the SN

if no host galaxy)

– The age (with respect to the restframe B band maximum of the LC).

– The contamination of the SN spectrum by the host galaxy.

– The type of the host.

SN Identification

Enough to built the Hubble diagram

(dL,z)

To c

ross

-ch

eck

th

e

resu

lts


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SN Identification (cont.)

SNIa = no H + strong Si II


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• It’s based on the 2 fitting of our spectrum with a model (local SNe + local galaxy).

• All the local spectra are into a database.

• These local spectra are from different type and different age (in the restframe) :

• 87 spectra from 8 SNIa

• 56 spectra from 5 peculiar SNIa

• 9 spectra from 2 SNIc

• 11 spectra from 1 IIP

•The database also contains a sample of galaxy spectra in case the host galaxy spectrum is not available.


The quality of the identification is limited by the diversity of the database


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Sobs(obs) – (Ssn(rest [1+z])+Sgal(rest [1+z]))


obs)

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• Loop over all the selected combinations of galaxie/SNe.

•Robustified fit (outliers like bad sky lines are discarded).

• One can fit on a given region only (eg. reject telluric absorptions).

•Sort the result by ascending 2.

Model with a galaxy template


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First (preliminary) results


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A bit of statistics for SNIa

<S/N> is about 3 per bin of ~3 Angstroms.

Redshift distribution <S/N>~ 3A distribution27 SNIa

<z>=0.55


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Example (Typical SNIa)

Best fit with sn1994d @ -2 days

R10D1-04A @ z = 0.687Texp = 2150s ;

<S/N>=5.95

Fit with host galaxy

No LC yet to check verify the age fitted.


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Example (Another SNIa)

Best fit with sn1994d (Ia) @ +2 days

• To date, the farthest SN of the SNLS programme.

• Database very poor in SNe with UV coverage.

R6D4-9 @ z=0.95 ;

No host galaxy

Texp= 2150s with Grism 300V (optic)

Texp= 2150s with Grism 300I (near IR)

<S/N>2.66A=4.46

Preliminary


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Example (Peculiar SNIa)SN2003ha @ z=0.285 ; Texp= 2150s Best fit with sn1999aa @ -

7days

sn1999aa is a peculiar SNIa, overluminous.

Good agreement with the LC

Preliminary

36% of peculiar SNIa expected (Li et al, 2000).

One of the farthest SNIa peculiar never observed.

SNLS will estimate the SNIa peculiar rate at large redshift.

<S/N>2.66A=12.6


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Example (non Ia SN)

Best fit with sn1994i @ +2 days

sn1994i is a SNIc.

Max of the LC 2 magnitudes weaker than a normal SNIa.

• Ic identification is difficult, very few SNIc spectra available in the litterature.

• Only one Ic in the SNLS sample, so far.

sn2003hb @ z=0.167 ; Texp= 2150s

<S/N>2.66A=11.0

Preliminary


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Conclusion

• After 6 months, more than 50 candidates spectroed.

• Already about 30 SNIa found between z~0.17 and z~0.95 with VLT (38 with the other telescopes).

• Beyond ID and redshift, VLT observations will allow us to do systematic and quantitative comparison of low z and high SNIa (evolution, rate of peculiars Ia...).

• This software gives quantitative tools to identify spectra.

Thank you !


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Back up slides


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Details of this analysis1. To discriminate between the first best

solutions

2. To discriminate between different type of SN


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Texp calculation : How does it work ?

The request is to get a minimum signal to noise ratio of 5, for a 10A binning, in the region from the calcium H&K and the magnesium MgII.

Ca H&K

MgII

z Texp(s)

0.3 70

0.4 160

0.5 370

0.6 910

0.7 1380

0.8 3060

0.9 6420


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Constraining the parameters

GUI in Tcl/Tk

snls : spectroscopy of supernovae with the vlt (status) grégory sainton lpnhe, cnrs/in2p3...

Documents

host galaxy spectrum

host spectrum

local spectra

host galaxy lines

sample of galaxy spectra

sn spectrum

host galaxythe age

universe sn identification