The 12 highest-redshift Type-Ia supernovae discovered to date. All of the supernovae in this table have redshifts greater than 1.5. Supernovae from the Subaru Deep Field are designated SNSDF, followed by the observation epoch in which they were discovered (0503 - March 2005). The other two supernovae in this table were discovered during the GOODS high-redshift supernova search, with the Hubble Space Telescope (HST). Our program has multiplied by sixfold the number of known Type-Ia supernovae at lookback times of 10 billion years.

The rate of Type-Ia supernovae as a function of redshift. The higher the redshift, the farther we look back in time (shown on the upper axis). The results from the Subaru Deep Field are shown as red symbols. The grey symbols are previously published supernova rate measurements. The curves are predictions of the supernova rate evolution, based on various proposed forms of the cosmic star formation history, convolved with a power-law Type-Ia supernova delay-time distribution. Our new measurements suggest that the Type-Ia supernova rate "levels off" at redshifts greater than about 0.7, with a rate about 5 times higher than in the present-day Universe (redshift zero). As seen in the figure, this behavior is in excellent agreement with expectations from Type-Ia supernova progenitor models with power-law delay functions, such as those expected from merging white dwarf progenitor models.

The production of iron in the Universe, as a function of redshift. The vertical axis is the mean abundance of iron in the Universe, relative to the iron abundance of the sun. The red curve shows the amount of iron produced by Type-Ia supernovae based on our rate measurements; the blue curve shows the amount produced by core-collapse supernovae; and the black curve is the total of the two. Each Type-Ia supernova produces, on average, 0.7 solar masses of iron. For the core-collapse component, it is assumed that 1% of the original star's mass was converted into iron. Our results permit the most reliable reconstruction to date of cosmic iron enrichment history.