The single-degenerate scenario for type Ia supernovae in cosmic perspective

The occurrence and properties of Type Ia supernovae (SN Ia's) in single-degenerate binary systems (white dwarf [WD] + nondegenerate companion) is examined for galaxies of different types and as a function of redshift. The rates and characteristics (peak luminosities, expansion velocities of the ejecta) expected from the explosion of mass-accreting WDs in symbiotic systems and ''helium star cataclysmics'' are found to be different from those arising in another class of candidate systems: cataclysmic-like (contact) systems (CLSs), where a CO WD accretes hydrogen on a thermal timescale from a Roche lobe-fiIling main-sequence or subgiant companion. We derive the evolution of the SN Ia rate and properties resulting from the thermonuclear explosion of sub-Chandrasekhar mass WDs in such systems when they detonate a helium layer accumulated from steady burning of hydrogen at the surface. A fraction of CLSs are believed to form a subset of the observed luminous supersoft X-ray sources (SSSs). Sub-Chandrasekhar explosions from CLSs are disfavored in all types of galaxies at redshifts z greater than or similar to 1. On the other hand, CLSs in which the WD succeeds to grow to the Chandrasekhar mass are more likely found in spiral galaxies and absent from early-type galaxies. SN Ia statistics could (if the uncertainties still involved are reduced) help to discriminate among proposed SN Ia scenarios. The range of variation of the characteristics of SN Ia's in the CLS scenario should be narrower than in symbiotics. The predicted correlation between peak luminosity and velocity of the ejecta in SN Ia's coming from these systems is weak. For CLSs, the distinction between the characteristics of SN Ia's respectively arising from sub-Chandrasekhar and from Chandrasekhar-mass explosions should be sharp, since all sub-Chandrasekhar explosions would be produced by low-mass WDs.