Type and redshift distributions

65 candidates have been observed between June 2003 and May 2004.

Redshift is measured by using emission and/or absorption lines of the host galaxy when it can be extracted separately from the candidate (about 67% of the observations). Otherwise, it is estimated by using the supernovae features.

The redshift distribution of type Ia supernovae is comprised between 0.2 and 0.95 (mean value =

0.55).

Host type identification

Identification is mainly based on two methods:

• A 2 fitting of the observed galaxy spectrum with the templates defined by Kinney and al.

• A Principal Component Analysis (PCA). This method decreases the number of variables and makes possible a spectral classification of the galaxies.

UV emission

For high redshift supernovae, the blue part of the optical spectrum correspond to the UV part of the rest-frame spectrum.

Observations at an intermediate redshift, z=0.5-0.6, offer a unique opportunity to observe UV emission.

Example of observed supernovae

Typical exposure time: 2160 to 3600 sec.

The VLT Spectroscopic Program of the SuperNova Legacy Survey

BASA Stéphane, on behalf of the SNLS collaboration*stephane.basa@oamp.fr, Laboratoire d’Astrophysique de Marseille

*Complete member list on http://cfht.hawaii.edu/SNLS

Analysis

Host Galaxy Type

Early E0,S0

Early Spiral Sa, Sb

Late Spiral & starburst

Fraction 27.3 % 30.3% 42.4 %

Type SNIa / SNIa?

SN IcSN II / SNII?

SN?AGN/QSO

and high-z galaxy

Number 37 1 3 12 12

The SuperNova Legacy Survey

Since August 2003, the SuperNova Legacy Survey (SNLS) collaboration is engaged in a new high redshift supernova survey using the newly commissioned 1 square degree wide field imager MegaPrime, a joint project of CFHT and CEA/DAPNIA.

The imaging program of SNLS is part of the CFHT Legacy Survey (CFHTLS) program, a large multi purpose imaging survey. It will use 202 dark/grey nights of observations over 5 years.

As a fundamental complement to these observations, a spectroscopic program is carried out on VLT, Gemini North and South, and Keck to identify supernova type and measure the redshift, but also to identify host galaxy type, study supernovae evolution, observe UV emission, …

The VLT spectroscopic program

ESO has allocated a Large Programme on FORS1 to the SNLS collaboration:

240 hours spread over 4 semesters.

“Real time” analysis

Spectra are reduced with a Midas pipeline and analyzed with home made programs:

• Production of 2D calibrated frames (wavelength and flux calibrated).

• Extraction of the candidate and of the host galaxy spectra if possible, with the associated statistical errors.

Delay between the observation submission and the spectrum analysis is reduced to less than 24 hr.

Identification method

It is based on a 2 fitting of the observed spectrum with a model which is a linear combination of supernova and galaxy templates.

.

Each combination is then weighted by the 2 probability to measure the supernova properties and the associated errors.

Conclusion

Between June 2003 and May 2004, 65 candidates have been observed by VLT and 37 type Ia supernovae identified with a redshift comprised between 0.2 and 0.95.

Primary program of the VLT Large Programme (type identification and redshift measurement) is fulfilled.

Thanks to the homogenous and large sample, many other studies are under way: host galaxy identification, UV emission, …

The program is ramping up: at the end of the SNLS program, more than 250 type Ia supernovae will be identified by VLT and 500 by VLT, Gemini and Keck.

obs)

2

Model composed of supernova and galaxy

templates

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

Observations

Sharing between the different spectroscopic telescopes follow very simple rules:

Bright candidates sent to VLT: smaller overheads.

Faint candidates equitably sent to VLT and Gemini.

VLT replaced by KECK for D3 field which is unobservable from Paranal.

Candidates are observed at their luminosity maximum to increase the Signal to Noise ratio.

All the VLT and Gemini observations are conducted in Service Mode

D4

D2

D1

D3

Ia at z=0.63

Texpo = 3600 sec.

SNIa / SNIA?

SNII / SNII ?

Ic at z=0.17

Ia at z=0.93

Peculiar Ia at z=0.28