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Verifying the cosmological utility of type Ia supernovae: implications of a dispersion in the ultraviolet spectra

Verifying the cosmological utility of type Ia supernovae: implications of a dispersion in the ultraviolet spectra
Verifying the cosmological utility of type Ia supernovae: implications of a dispersion in the ultraviolet spectra
We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe Ia) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40% of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high quality local spectra. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see are much larger than predicted in recent models and do not follow expected patterns. An interesting new result is a variation seen in the wavelength of selected UV features with phase. We also demonstrate systematic differences in the SN Ia spectral features with SN light curve width in both the UV and the optical. We show that these intrinsic variations could represent a statistical limitation in the future use of high-redshift SNe Ia for precision cosmology. We conclude that further detailed studies are needed, both locally and at moderate redshift where the rest-frame UV can be studied precisely, in order that future missions can confidently be planned to fully exploit SNe Ia as cosmological probes.
0004-637X
51-69
Ellis, R.S.
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Sullivan, M.
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Nugent, P.E.
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Howell, D.A.
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Gal‐Yam, A.
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Astier, P.
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Balam, D.
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Balland, C.
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Basa, S.
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Carlberg, R.G.
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Conley, A.
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Fouchez, D.
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Guy, J.
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Hardin, D.
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Hook, I.
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Pain, R.
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Perrett, K.
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Pritchet, C.J.
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Regnault, N.
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Ellis, R.S.
bf153fc2-2ab9-495b-913c-2f849ad42225
Sullivan, M.
2f31f9fa-8e79-4b35-98e2-0cb38f503850
Nugent, P.E.
f0687239-eb10-4873-8722-df0ba0b4e228
Howell, D.A.
1a20d5f3-d2c4-43d6-88d7-c548eee8482f
Gal‐Yam, A.
32060b88-6fbc-42cc-9ec3-1de2842aa0e5
Astier, P.
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Balam, D.
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Balland, C.
48ce478e-1576-460d-9265-4ef9df68e4c7
Basa, S.
333c3ee4-fd63-41b6-8660-2c7820cc63fe
Carlberg, R.G.
f1b0b390-a865-49ee-97bf-0e8ee24d1cbe
Conley, A.
c5ebe222-8796-4110-ac6d-f7143d52ab30
Fouchez, D.
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Guy, J.
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Hardin, D.
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Hook, I.
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Pain, R.
de4d755a-4039-4aab-8aa1-640439d410e2
Perrett, K.
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Pritchet, C.J.
a378632e-e32b-42e7-961c-4fd19805c806
Regnault, N.
76d4cc71-48cf-44a6-b295-77fc4e96183d

Ellis, R.S., Sullivan, M., Nugent, P.E., Howell, D.A., Gal‐Yam, A., Astier, P., Balam, D., Balland, C., Basa, S., Carlberg, R.G., Conley, A., Fouchez, D., Guy, J., Hardin, D., Hook, I., Pain, R., Perrett, K., Pritchet, C.J. and Regnault, N. (2008) Verifying the cosmological utility of type Ia supernovae: implications of a dispersion in the ultraviolet spectra. The Astrophysical Journal, 674 (1), 51-69. (doi:10.1086/524981).

Record type: Article

Abstract

We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe Ia) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40% of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high quality local spectra. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see are much larger than predicted in recent models and do not follow expected patterns. An interesting new result is a variation seen in the wavelength of selected UV features with phase. We also demonstrate systematic differences in the SN Ia spectral features with SN light curve width in both the UV and the optical. We show that these intrinsic variations could represent a statistical limitation in the future use of high-redshift SNe Ia for precision cosmology. We conclude that further detailed studies are needed, both locally and at moderate redshift where the rest-frame UV can be studied precisely, in order that future missions can confidently be planned to fully exploit SNe Ia as cosmological probes.

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Published date: 10 February 2008
Organisations: Astronomy Group

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Local EPrints ID: 350442
URI: https://eprints.soton.ac.uk/id/eprint/350442
ISSN: 0004-637X
PURE UUID: 0176ab48-c3d6-4472-934c-40d5613701a1
ORCID for M. Sullivan: ORCID iD orcid.org/0000-0001-9053-4820

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Date deposited: 04 Apr 2013 11:40
Last modified: 31 Jul 2019 00:34

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Contributors

Author: R.S. Ellis
Author: M. Sullivan ORCID iD
Author: P.E. Nugent
Author: D.A. Howell
Author: A. Gal‐Yam
Author: P. Astier
Author: D. Balam
Author: C. Balland
Author: S. Basa
Author: R.G. Carlberg
Author: A. Conley
Author: D. Fouchez
Author: J. Guy
Author: D. Hardin
Author: I. Hook
Author: R. Pain
Author: K. Perrett
Author: C.J. Pritchet
Author: N. Regnault

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