Journal
ASTROPHYSICAL JOURNAL
Volume 685, Issue 2, Pages 752-766Publisher
IOP PUBLISHING LTD
DOI: 10.1086/590659
Keywords
cosmology : observations; galaxies : elliptical and lenticular, cD galaxies : fundamental parameters; supernovae : general
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Funding
- NASA LTSA [NAG5-9364]
- NSF [AST 06-06772, AST 06-07485]
- TABASGO Foundation
- Sun Microsystems, Inc.
- Hewlett-Packard Company
- AutoScope Corporation
- Lick Observatory
- University of California
- Sylvia and Jim Katzman Foundation
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We have obtained optical spectra of 29 early-type (E/S0) galaxies that hosted Type Ia supernovae (SNe Ia). We have measured absorption-line strengths and compared them to a grid of models to extract the relations between the supernova properties and the luminosity-weighted age/composition of the host galaxies. Such a direct measurement is a marked improvement over existing analyses that tend to rely on general correlations between the properties of stellar populations and morphology. We find a strong correlation suggesting that SNe Ia in galaxies whose populations have a characteristic age greater than 5 Gyr are similar to 1 mag fainter at V-max than those found in galaxies with younger populations. We find that SN Ia distance residuals in the Hubble diagram are correlated with host-galaxy metal abundance with higher iron abundance galaxies hosting less-luminous supernovae. We thus conclude that the time since progenitor formation primarily determines the radioactive Ni production while progenitor metal abundance has a weaker influence on peak luminosity, but one not fully corrected by light-curve shape and color fitters. This result, particularly the secondary dependence on metallicity, has significant implications for the determination of the equation-of-state parameter, w = P/(rho c(2)), and could impact planning for future dark-energy missions such as JDEM. Assuming no selection effects in discovering SNe Ia in local early-type galaxies, we find a higher specific SN Ia rate in E/S0 galaxies with ages below 3 Gyr than in older hosts. The higher rate and brighter luminosities seen in the youngest E/S0 hosts may be a result of recent star formation and represents a tail of the ''prompt'' SN Ia progenitors.
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