Luminosity distributions of Type Ia supernovae

We have assembled a dataset of 165 low redshift, z<0. 06, publicly available type Ia supernovae (SNe Ia). We produce maximum light magnitude (M₁ and Mₕ) distributions of SNe Ia to explore the diversity of parameter space that they can fill. Before correction for host galaxy extinction we find that the mean M₁ and Mₕ of SNe Ia are -18. 58\0. 07mag and -18. 72\0. 05mag respectively. Host galaxy extinction is corrected using a new method based on the SN spectrum. After correction, the mean values of M₁ and Mₕ of SNe Ia are -19. 10\0. 06 and -19. 10\0. 05mag respectively. After correction for host galaxy extinction, `normal' SNeIa (\ m₁₅ (B) <1. 6mag) fill a larger parameter space in the Width-Luminosity Relation (WLR) than previously suggested, and there is evidence for luminous SNe Ia with large \ m₁₅ (B). We find a bimodal distribution in \ m₁₅ (B), with a pronounced lack of transitional events at \ m₁₅ (B) =1. 6 mag. We confirm that faster, low-luminosity SNe tend to come from passive galaxies. Dividing the sample by host galaxy type, SNe Ia from star-forming (S-F) galaxies have a mean M₁=-19. 20 \ 0. 05 mag, while SNe Ia from passive galaxies have a mean M₁=-18. 57 \ 0. 24 mag. Even excluding fast declining SNe, `normal' (M₁<-18 mag) SNe Ia from S-F and passive galaxies are distinct. In the V-band, there is a difference of 0. 4 \ 0. 13 mag between the median (Mₕ) values of the `normal' SN Ia population from passive and S-F galaxies. This is consistent with (\ 15 \ 10) % of `normal' SNe Ia from S-F galaxies coming from an old stellar population.