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Published November 1, 2012 | Published + Accepted Version
Journal Article Open

Hubble Space Telescope studies of low-redshift Type Ia supernovae: evolution with redshift and ultraviolet spectral trends

Abstract

We present an analysis of the maximum light, near-ultraviolet (NUV; 2900 < λ < 5500 Å) 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 (3σ), 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.

Additional Information

© 2012 The Authors. Monthly Notices of the Royal Astronomical Society. Accepted 2012 August 10; Received 2012 August 10; in original form 2012 May 29. Article first published online: 10 Oct. 2012. MS acknowledges support from the Royal Society. AG-Y and MS acknowledge support from the Weizmann-UK 'making connections' programme. AG-Y further acknowledges support by the ISF, BSF, a Minerva grant, the ARCHES award and the Lord Sieff of Brompton Fund. DAH and BD are supported by the Las Cumbres Observatory Global Telescope Network. MMK acknowledges generous support from the Hubble Fellowship and Carnegie-Princeton Fellowship. EOO is incumbent of the Arye Dissentshik career development chair and is grateful to support by a grant from the Israeli Ministry of Science. This paper is based on observations made with the NASA/ESA HST, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programmes 11721 and 12298. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Observations were obtained with the Samuel Oschin Telescope at the Palomar Observatory as part of the Palomar Transient Factory project, a scientific collaboration between the California Institute of Technology, Columbia University, La Cumbres Observatory, the Lawrence Berkeley National Laboratory, the National Energy Research Scientific Computing Center, the University of Oxford and the Weizmann Institute of Science. The William Herschel Telescope is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Some of the data were obtained with the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. These observations were made possible by the generous financial support of the W. M. Keck Foundation. This paper uses observations obtained with facilities of the LCOGT. The BOS is operated by the Las Cumbres Observatory Global Telescope Network and is located at the Sedgwick Reserve, a part of the University of California Natural Reserve System. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This publication has been made possible by the participation of more than 10 000 volunteers in the Galaxy Zoo: Supernovae project (http://supernova.galaxyzoo.org/authors).

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August 22, 2023
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