SPECTRAL ENERGY DISTRIBUTION OF z ≳ 1 TYPE Ia SUPERNOVA HOSTS IN GOODS: CONSTRAINTS ON EVOLUTIONARY DELAY AND THE INITIAL MASS FUNCTION

We identify a sample of 22 host galaxies of Type Ia Supernovae (SNe Ia) at redshifts 0.95 < z < 1.8 discovered in the Hubble Space Telescope (HST) observations of the Great Observatories Origins Deep Survey (GOODS) fields. We measure the photometry of the hosts in Spitzer Space Telescope and ground-based imaging of the GOODS fields to provide flux densities from the U band to 24 mu m. We fit the broadband photometry of each host with simple stellar population models to estimate the age of the stellar population giving rise to the SN Ia explosions. We break the well-known age-extinction degeneracy in such analyses using the Spitzer 24 mu m data to place upper limits on the thermally reprocessed, far-infrared emission from dust. The ages of these stellar populations give us an estimate of the delay times between the first epoch of star formation in the galaxies and the explosion of the SNe Ia. We find a bi-modal distribution of delay times ranging from 0.06 to 4.75 Gyr although at the 95% confidence interval, the delay time distribution is consistent with a single power law as well. We also constrain the first epoch of low-mass star formation using these results, showing that stars of mass less than or similar to 8 M circle dot were formed within 3 Gyr after the big bang and possibly by z similar to 6. This argues against a truncated stellar initial mass function in high-redshift galaxies.