Delay time distribution measurement of type Ia supernovae by the Subaru/XMM-Newton deep survey and implications for the progenitor

Abstract

The delay time distribution (DTD) of type Ia supernovae (SNe Ia) from star formation is an important clue to reveal the still unknown progenitor system of SNe Ia. Here, we report on a measurement of the SN Ia DTD in a delay time range of tIa = 0.1-8.0 Gyr by using faint variable objects detected in the Subaru/XMM-Newton Deep Survey (SXDS) down to i′ ∼ 25.5. We selected 65 SN candidates showing significant spatial offset from the nuclei of the host galaxies having an old stellar population at z ∼ 0.4-1.2, out of more than 1000 SXDS variable objects. Although spectroscopic type classification is not available for these, we quantitatively demonstrated that more than ∼ 80% of these should be SNe Ia. The DTD was derived using stellar age estimates of the old galaxies based on 9 band photometries from optical to mid-infrared wavelength. Combined with the observed SN Ia rate in elliptical galaxies at the local universe, the DTD in tIa ∼ 0.1-10 Gyr is well described by a featureless power-law as fD (tIa) ∝ t Iaα with α ∼ - 1. The derived DTD is in excellent agreement with a generic prediction of the double-degenerate scenario, giving strong support to this scenario. In the single-degenerate (SD) scenario, although predictions by simple analytic formulations have broad DTD shapes that are similar to the observation, DTD shapes calculated by more detailed binary population synthesis tend to have strong peaks at characteristic time scales, which do not fit the observation. This result thus indicates either that the SD channel is not the major contributor to SNe Ia in an old stellar population, or that an improvement of binary population synthesis theory is required. Various sources of systematic uncertainties were examined and tested, but our main conclusions were not affected significantly. © 2008. Astronomical Society of Japan.