Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 426, Issue 3, Pages 2359-2379Publisher
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2012.21909.x
Keywords
supernovae: general; galaxies: general; distance scale; cosmological parameters
Categories
Funding
- Royal Society
- Weizmann-UK
- ISF
- BSF
- Minerva grant
- ARCHES award
- Lord Sieff of Brompton Fund
- Las Cumbres Observatory Global Telescope Network
- Israeli Ministry of Science
- NASA [NAS 5-26555]
- UK Science and Technology Facilities Council
- W. M. Keck Foundation
- National Aeronautics and Space Administration
- Hubble Fellowship
- Carnegie-Princeton Fellowship
- Direct For Education and Human Resources
- Division Of Research On Learning [0941610] Funding Source: National Science Foundation
- Science and Technology Facilities Council [ST/G009465/1, ST/H002456/1, PP/E001149/1, ST/G004331/1, ST/H000704/1, ST/H002391/1, ST/I003673/1, ST/J001465/1, PP/E003427/1] Funding Source: researchfish
- STFC [PP/E001149/1, ST/H000704/1, ST/H002456/1, PP/E003427/1, ST/I003673/1, ST/H002391/1, ST/G009465/1, ST/G004331/1, ST/J001465/1] Funding Source: UKRI
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We present an analysis of the maximum light, near-ultraviolet (NUV; 2900 < lambda < 5500 angstrom) spectra of 32 low-redshift (0.001 < z < 0.08) Type Ia supernovae (SNe Ia), obtained with the Hubble Space Telescope (HST) using the Space Telescope Imaging Spectrograph. We combine this spectroscopic sample with high-quality gri light curves obtained with robotic telescopes to measure SN Ia photometric parameters, such as stretch (light-curve width), optical colour and brightness (Hubble residual). By comparing our new data to a comparable sample of SNe Ia at intermediate redshift (0.4 < z < 0.9), we detect modest spectral evolution (3s), in the sense that our mean low-redshift NUV spectrum has a depressed flux compared to its intermediate-redshift counterpart. We also see a strongly increased dispersion about the mean with decreasing wavelength, confirming the results of earlier surveys. We show that these trends are consistent with changes in metallicity as predicted by contemporary SN Ia spectral models. We also examine the properties of various NUV spectral diagnostics in the individual SN spectra. We find a general correlation between SN stretch and the velocity (or position) of many NUV spectral features. In particular, we observe that higher stretch SNe have larger Ca ii H&K velocities, which also correlate with host galaxy stellar mass. This latter trend is probably driven by the well-established correlation between stretch and host galaxy stellar mass. We find no significant trends between UV spectral features and optical colour. Mean spectra constructed according to whether the SN has a positive or negative Hubble residual show very little difference at NUV wavelengths, indicating that the NUV evolution and variation we identify does not directly correlate with Hubble diagram residuals. Our work confirms and strengthens earlier conclusions regarding the complex behaviour of SNe Ia in the NUV spectral region, but suggests the correlations we find are more useful in constraining progenitor models rather than improving the use of SNe Ia as cosmological probes.
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