Supernovae in Early‐Type Galaxies: Directly Connecting Age and Metallicity with Type Ia Luminosity
Gallagher, Joseph S.
Garnavich, Peter M.
Kirshner, Robert P.
Jha, Saurabh W.
Filippenko, Alexei V.
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CitationGallagher, Joseph S., Peter M. Garnavich, Nelson Caldwell, Robert P. Kirshner, Saurabh W. Jha, Weidong Li, Mohan Ganeshalingam, and Alexei V. Filippenko. 2008. “Supernovae in Early‐Type Galaxies: Directly Connecting Age and Metallicity with Type Ia Luminosity.” The Astrophysical Journal 685 (2): 752–66. https://doi.org/10.1086/590659.
AbstractWe 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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