The VLT spectral set of the final two years of SNLS

Table of Contents

This page presents 70 spectra of 68 SNe Ia observed at the VLT during the final two years of the SNLS experiment. This set supplements the VLT 3-year set presented here. This release comes along with the paper Balland et al. 2018, accepted in A&A.

1 Release presentation

The sample

This release contains the SNeIa spectra observed at the Very Large Telescope from August, 1st 2006 up to the end of the SNLS survey mid-2008.

To this set, we add 8 SNeIa spectra that were acquired in Multi Object Spectroscopy (MOS) mode before August, 1st 2006 but that were not included in the 3-year SNLS VLT spectral sample as the extraction pipeline used for that analysis did not support MOS mode (those are SN 05D1dx, SN 05D1hm, SN 05D1if, SN 05D2le, SN 06D2ag, SN 06D4ba, SN 06D4bo and SN 06D4bw).

For completeness, we further add the spectrum of SN 06D2bo, a Type Ia supernova measured in Long Slit Spectroscopy (LSS) mode in February 2006 that was initially misclassified as a non-SNIa object.

In total, 70 spectra of 68 SNeIa identified as SNeIa are presented.

Data acquisition and reduction

Up until the beginning of September 2005, all the real-time spectroscopic follow-up with FORS1 and FORS2 was done in long slit mode. From September 2005 onwards we used the MOS mode of FORS1 and FORS2 to target live transients, the host of any other transient that happened to be within the FORS2 field of view and randomly selected field galaxies.

We used one of two setups with FORS. If the SN was likely to be below z ~ 0.7, we used the 300V grism with the GG435 order sorting filter. If it was likely to be at a higher redshift we used the 300I grism with the OG590 order sorting filter. The slit widths were set to 1 arcsec. Each spectrum is calibrated in wavelength and flux. Differential slit losses were corrected by the atmospheric dispersion corrector. Residual losses were taken into account with the recalibration procedure described in the accompanying paper. No correction of telluric feature was performed. For the SNe, we also computed an error spectrum derived from Poisson noise in regions of the 2D sky-subtracted spectrum that are free of objects.

Redshift and phase estimates

Redshifts are estimated from strong spectral features when present and are not corrected to the heliocentric reference frame. The most commonly identified host features in the spectra are emission lines from the [OII] unresolved λλ3727, 3729 doublet, Hβ λ4861, the [OIII] doublet λλ4959,5007, Hα λ 6563 and absorption lines from higher order Balmer transitions, and CaII H& K λλ3934, 3968. We assign an error of δ z ~ 0.001 on the redshift derived from the host lines width. About 75% of the redshifts of our sample come from host spectral lines.

If there is no apparent host line, the redshift is estimated from the supernova features themselves. We assign an error of δ z ~ 0.01 on the supernova redshifts.

The spectrum phase is computed from the best-fit date of maximum light and the MJD date of the spectrum.

SN identification

A combined fit of observed lightcurves and spectra was performed with SALT2 (Guy etal 2007) using a χ2 minization procedure. A galaxy component modeling the host-galaxy is added to the SN model to take into account host-galaxy contamination. The overall fraction of the host-galaxy in the full model is a free parameter that is adjusted during the fit. Host-galaxy models include PEGASE2 synthetic templates (Fioc & Rocca-Volmerange 1997, 1999) for elliptical (E), lenticular (S0), Sa, Sb, Sc and Sd Hubble types at various ages. We also consider Kinney et al 1996 templates for the same types, excluding Sc and Sd. The best-fit host-galaxy model is obtained by interpolation between two contiguous types in the Kinney template sequence or two contiguous galaxy ages in the PEGASE2 templates. The final supernova spectrum is obtained by subtracting the best fit host-galaxy model from the full spectrum. We do not add host-galaxy lines to the PEGASE2 templates and, consequently, line residuals often contaminate the final SN spectrum.

Catalog of non SNIa MOS objects

The observations with FORS1 and FORS2 allowed us to target up to 19 objects simultaneously. One of the slits was always placed on the active supernova. The other 18 were placed on a variety of targets, which included the host-galaxy galaxies of SNLS supernovae that had faded from view, variable sources, and randomly selected field galaxies. Also listed are the supernovae that were not SNe Ia. These supernovae were predominantely Type II SNe. About a sixth of the SNLS five year SN sample was observed with the MOS mode of FORS1 and FORS2

Accompagnying paper

The ESO’s VLT Type Ia supernova spectral set of the final two years of SNLS

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

Reference: Balland, C. etal (2018)

Grab a copy here

2 Download


The full spectral set of the last two years of SNLS can be downloaded here as a single tar file. All spectra are in the observer frame and are host subtracted (see paper).

Spectra files

There is one ASCII file for each spectrum.
- 1st column, Pixel number
- 2nd column, Wavelength: Lambda in angstroems
- 3rd column, SN Flux: supernova flux in physical units (erg/s/cm2/A/1e-16)
- 4th column, SN Fluxerr: statistical error for the flux measurement
Example (07D1bu: snonly_07D1bu_1711_Balland_etal_17.dat):

@Telescope VLT
@Reference Balland etal (2017)
@Redshift 0.626
@Galaxy-Model Sd5
@Spectrum spectrum_07D1bu_1711.dat
@SN-Name 07D1bu
@Phase -2.910
@Survey SNLS
@SN-Type SNIa
@Date 2007-09-08
@Units 1.e-16 erg/s/cm2/A
@Galaxy-Fraction 0.4700
# XPIX :
# WAVE :
# SN_ERR :
0   4255.530       0.00083       0.00393
1   4260.530       0.00283       0.00429
2   4265.530       0.00099       0.00462
3   4270.530      -0.00057       0.00405
4   4275.530      -0.00150       0.00437
5   4280.530      -0.00200       0.00325
6   4285.530       0.00217       0.00284
7   4290.530       0.00346       0.00259
8   4295.530       0.00341       0.00317
9   4300.530       0.00066       0.00280
10   4305.530       0.00075       0.00279
11   4310.530      -0.00156       0.00251
12   4315.530      -0.00188       0.00235

Catalog of non SNIa MOS objects

The catalog of non SNIa MOS objects can be downloaded here

Author: Christophe Balland

Created: 2017-12-19 mar. 9:00

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