Luminosity distributions of Type Ia supernovae.

We have assembled a data set of 165 low redshift, z < 0.06, publicly available Type Ia supernovae (SNe Ia). We produce maximum light magnitude (M_B and M_V) 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 M_B and M_V of SNe Ia are -18.58 ± 0.07 and -18.72 ± 0.05 mag, respectively. Host galaxy extinction is corrected using a new method based on the SN spectrum. After correction, the mean values of M_B and M_V of SNe Ia are -19.10 ± 0.06 and -19.10 ± 0.05 mag, respectively. After correction for host galaxy extinction, 'normal' SNe Ia (Δm₁₅(B) < 1.6 mag) fill a larger parameter space in the width-luminosity relation than previously suggested, and there is evidence for luminous SNe Ia with large Δm₁₅(B). We find a bimodal distribution in Δm₁₅(B), with a pronounced lack of transitional events at Δm₁₅(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 MB = -19.20 ± 0.05 mag, while SNe Ia from passive galaxies have a mean MB = -18.57 ± 0.24 mag. Even excluding fast declining SNe, 'normal' (MB < -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 (MV) values of the 'normal' SN Ia population from passive and S-F galaxies. This is consistent with (~15 ± 10) per cent of 'normal' SNe Ia from S-F galaxies coming from an old stellar population. [ABSTRACT FROM AUTHOR]