2016MNRAS.460.3529A

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 (Δm_15(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 Δm_15(B). We find a bimodal distribution in Δm_15(B), with a pronounced lack of transitional events at Δm_15(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 M_B=-19.20±0.05 mag, while SNe Ia from passive galaxies have a mean M_B=-18.57±0.24 mag. Even excluding fast declining SNe, 'normal' (M_B < -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 (M_V) 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.