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The ESO's VLT type Ia supernova spectral set of the final two years of SNLS

The ESO's VLT type Ia supernova spectral set of the final two years of SNLS
The ESO's VLT type Ia supernova spectral set of the final two years of SNLS
Aims. We aim to present 70 spectra of 68 new high-redshift type Ia supernovae (SNe Ia) measured at ESO's VLT during the final two years of operation (2006-2008) of the Supernova Legacy Survey (SNLS). This new sample complements the VLT three year spectral set. Altogether, these two data sets form the five year sample of SNLS SN Ia spectra measured at the VLT on which the final SNLS cosmological analysis will partly be based. In the redshift range considered, this sample is unique in terms of homogeneity and number of spectra. We use it to investigate the possibility of a spectral evolution of SNe Ia populations with redshift as well as SNe Ia spectral properties as a function of lightcurve fit parameters and the mass of the host-galaxy. Methods. Reduction and extraction are based on both IRAF standard tasks and our own reduction pipeline. Redshifts are estimated from host-galaxy lines whenever possible or alternatively from supernova features. We used the spectro-photometric SN Ia model SALT2 combined with a set of galaxy templates that model the host-galaxy contamination to assess the type Ia nature of the candidates. Results. We identify 68 new SNe Ia with redshift ranging from z = 0.207 to z = 0.98 for an average redshift of z = 0.62. Each spectrum is presented individually along with its best-fit SALT2 model. Adding this new sample to the three year VLT sample of SNLS, the final dataset contains 209 spectra corresponding to 192 SNe Ia identified at the VLT. We also publish the redshifts of other candidates (host galaxies or other transients) whose spectra were obtained at the same time as the spectra of live SNe Ia. This list provides a new redshift catalog useful for upcoming galaxy surveys. Using the full VLT SNe Ia sample, we build composite spectra around maximum light with cuts in color, the lightcurve shape parameter ("stretch"), host-galaxy mass and redshift. We find that high-z SNe Ia are bluer, brighter and have weaker intermediate mass element absorption lines than their low-z counterparts at a level consistent with what is expected from selection effects. We also find a flux excess in the range [3000-3400] Å for SNe Ia in low mass host-galaxies (M <1010M⊙) or with locally blue U-V colors, and suggest that the UV flux (or local color) may be used in future cosmological studies as a third standardization parameter in addition to stretch and color.
Cosmology: observations, Methods: data analysis, Supernovae: general, Techniques: spectroscopic
0004-6361
Balland, C.
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Cellier-Holzem, F.
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Lidman, C.
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Astier, P.
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Betoule, M.
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Carlberg, R.G.
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Conley, A.
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Ellis, R.S.
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Guy, J.
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Hardin, D.
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Hook, I.M.
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Howell, D.A.
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Pain, R.
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Pritchet, C.J.
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Regnault, N.
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Sullivan, M.
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Arsenijevic, V.
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Baumont, S.
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El-Hage, P.
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Fabbro, S.
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Fouchez, D.
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Mitra, A.
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Möller, A.
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Mourão, A.M.
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Neveu, J.
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Roman, M.
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Ruhlmann-Kleider, V.
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Balland, C.
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Cellier-Holzem, F.
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Lidman, C.
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Astier, P.
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Betoule, M.
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Carlberg, R.G.
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Conley, A.
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Ellis, R.S.
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Guy, J.
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Hardin, D.
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Hook, I.M.
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Howell, D.A.
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Pain, R.
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Pritchet, C.J.
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Regnault, N.
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Sullivan, M.
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Arsenijevic, V.
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Baumont, S.
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El-Hage, P.
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Fabbro, S.
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Fouchez, D.
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Mitra, A.
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Möller, A.
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Mourão, A.M.
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Neveu, J.
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Roman, M.
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Ruhlmann-Kleider, V.
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Balland, C., Cellier-Holzem, F., Lidman, C., Astier, P., Betoule, M., Carlberg, R.G., Conley, A., Ellis, R.S., Guy, J., Hardin, D., Hook, I.M., Howell, D.A., Pain, R., Pritchet, C.J., Regnault, N., Sullivan, M., Arsenijevic, V., Baumont, S., El-Hage, P., Fabbro, S., Fouchez, D., Mitra, A., Möller, A., Mourão, A.M., Neveu, J., Roman, M. and Ruhlmann-Kleider, V. (2018) The ESO's VLT type Ia supernova spectral set of the final two years of SNLS. Astronomy & Astrophysics, 614. (doi:10.1051/0004-6361/201731924).

Record type: Article

Abstract

Aims. We aim to present 70 spectra of 68 new high-redshift type Ia supernovae (SNe Ia) measured at ESO's VLT during the final two years of operation (2006-2008) of the Supernova Legacy Survey (SNLS). This new sample complements the VLT three year spectral set. Altogether, these two data sets form the five year sample of SNLS SN Ia spectra measured at the VLT on which the final SNLS cosmological analysis will partly be based. In the redshift range considered, this sample is unique in terms of homogeneity and number of spectra. We use it to investigate the possibility of a spectral evolution of SNe Ia populations with redshift as well as SNe Ia spectral properties as a function of lightcurve fit parameters and the mass of the host-galaxy. Methods. Reduction and extraction are based on both IRAF standard tasks and our own reduction pipeline. Redshifts are estimated from host-galaxy lines whenever possible or alternatively from supernova features. We used the spectro-photometric SN Ia model SALT2 combined with a set of galaxy templates that model the host-galaxy contamination to assess the type Ia nature of the candidates. Results. We identify 68 new SNe Ia with redshift ranging from z = 0.207 to z = 0.98 for an average redshift of z = 0.62. Each spectrum is presented individually along with its best-fit SALT2 model. Adding this new sample to the three year VLT sample of SNLS, the final dataset contains 209 spectra corresponding to 192 SNe Ia identified at the VLT. We also publish the redshifts of other candidates (host galaxies or other transients) whose spectra were obtained at the same time as the spectra of live SNe Ia. This list provides a new redshift catalog useful for upcoming galaxy surveys. Using the full VLT SNe Ia sample, we build composite spectra around maximum light with cuts in color, the lightcurve shape parameter ("stretch"), host-galaxy mass and redshift. We find that high-z SNe Ia are bluer, brighter and have weaker intermediate mass element absorption lines than their low-z counterparts at a level consistent with what is expected from selection effects. We also find a flux excess in the range [3000-3400] Å for SNe Ia in low mass host-galaxies (M <1010M⊙) or with locally blue U-V colors, and suggest that the UV flux (or local color) may be used in future cosmological studies as a third standardization parameter in addition to stretch and color.

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The ESO’s VLT Type Ia supernova spectral set of the final two years - Accepted Manuscript
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Accepted/In Press date: 6 December 2017
e-pub ahead of print date: 29 June 2018
Published date: June 2018
Keywords: Cosmology: observations, Methods: data analysis, Supernovae: general, Techniques: spectroscopic

Identifiers

Local EPrints ID: 422644
URI: https://eprints.soton.ac.uk/id/eprint/422644
ISSN: 0004-6361
PURE UUID: 52b2acd1-0975-423d-b56f-e09218a865d2
ORCID for M. Sullivan: ORCID iD orcid.org/0000-0001-9053-4820

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Date deposited: 27 Jul 2018 16:30
Last modified: 14 Mar 2019 01:35

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Contributors

Author: C. Balland
Author: F. Cellier-Holzem
Author: C. Lidman
Author: P. Astier
Author: M. Betoule
Author: R.G. Carlberg
Author: A. Conley
Author: R.S. Ellis
Author: J. Guy
Author: D. Hardin
Author: I.M. Hook
Author: D.A. Howell
Author: R. Pain
Author: C.J. Pritchet
Author: N. Regnault
Author: M. Sullivan ORCID iD
Author: V. Arsenijevic
Author: S. Baumont
Author: P. El-Hage
Author: S. Fabbro
Author: D. Fouchez
Author: A. Mitra
Author: A. Möller
Author: A.M. Mourão
Author: J. Neveu
Author: M. Roman
Author: V. Ruhlmann-Kleider

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