The ESO/VLT 3rd year Type Ia supernova data set from the supernova legacy survey

Abstract

Aims. We present 139 spectra of 124 Type Ia supernovae (SNe Ia) that were observed at the ESO/VLT during the first three years of the Canada-France-Hawaï Telescope (CFHT) supernova legacy survey (SNLS). This homogeneous data set is used to test for redshift evolution of SN Ia spectra, and will be used in the SNLS 3rd year cosmological analyses. Methods. Spectra have been reduced and extracted with a dedicated pipeline that uses photometric information from deep CFHT legacy survey (CFHT-LS) reference images to trace, at sub-pixel accuracy, the position of the supernova on the spectrogram as a function of wavelength. It also separates the supernova and its host light in ∼60% of cases. The identification of the supernova candidates is performed using a spectrophotometric SN Ia model. Results. A total of 124 SNe Ia, roughly 50% of the overall SNLS spectroscopic sample, have been identified using the ESO/VLT during the first three years of the survey. Their redshifts range from z = 0.149 to z = 1.031. The average redshift of the sample is z = 0.63 ± 0.02. This constitutes the largest SN Ia spectral set to date in this redshift range. The spectra are presented along with their best-fit spectral SN Ia model and a host model where relevant. In the latter case, a host subtracted spectrum is also presented. We produce average spectra for pre-maximum, maximum and post-maximum epochs for both z < 0.5 and z ≥ 0.5 SNe Ia. We find that z < 0.5 spectra have deeper intermediate mass element absorptions than z ≥ 0.5 spectra. The differences with redshift are consistent with the selection of brighter and bluer supernovae at higher redshift.

Extending the supernova Hubble diagram toz~ 1.5 with theEuclidspace mission

“…This is known to be feasible at z < 1 (e.g. Zheng et al 2008;Balland et al 2009;Blondin et al 2012). In the next decade, we can seriously consider extending the spectroscopic comparisons of SNe across redshifts and host types to higher redshifts than currently available: both the JWST and ground-based extremely large telescopes (Hook 2013) will provide relatively easy access to mid-resolution spectroscopy of faint targets (m ∼ 26) in the NIR, not practical with current instruments.…”

Photometric redshifts for type Ia supernovae in the supernova legacy survey

“…It originates from the union of two sources: 241 are real-time selected events confirmed as "Ia" or "Ia?" by spectroscopy (Howell 2005;Bronder et al 2008;Ellis et al 2008;Balland et al 2009), and the additional 48 are issued from a SN Ia photometric selection by Bazin et al (in prep. ) based on the host galaxy photometric redshift.…”

BAHAMAS: NEW ANALYSIS OF TYPE Ia SUPERNOVAE REVEALS INCONSISTENCIES WITH STANDARD COSMOLOGY

“…The accelerated expansion is currently widely attributed to the existence of a "dark energy" component, which is compatible with Einsteinʼs cosmological constant. Over the last decade, the sample of SNe Ia has increased dramatically (e.g., Astier et al 2006;Wood-Vasey et al 2007;Bailey et al 2008;Kowalski et al 2008;Balland et al 2009;Freedman et al 2009;Hicken et al 2009;Kessler et al 2009;Amanullah et al 2010;Contreras et al 2010;Suzuki et al 2012;Betoule et al 2014;Rest et al 2014), and it now comprises several hundred spectroscopically confirmed SNe Ia. Since SNe Ia probe the low-redshift universe, they are ideal tools to measure the properties of dark energy.…”