Ejecta mass diagnostics of Type Ia supernovae

We present one-dimensional non-local thermodynamic equilibrium time-dependent radiative transfer simulations (using CMFGEN) of two sub-Chandrasekhar (sub-M-Ch), one M-Ch and one super-M-Ch Type Ia SN ejecta models. Three originate from M-Ch delayed detonation models, and the fourth is a sub-M-Ch detonation model. Ejecta masses are 1.02, 1.04, 1.40 and 1.70 M-circle dot, and all models have 0.62 M-circle dot of Ni-56. Sub-M-Ch model light curves evolve faster, reaching bolometric maximum 2-3 d earlier and having 3-4 d shorter bolometric half-light widths. The models vary by similar to 12 per cent at maximum bolometric luminosity and by 0.17 mag in B-max. While Delta M-15(B) increases with ejecta mass, it only varies by similar to 5 per cent around 1mag. Sub-M-Ch models are 0.25 mag bluer in B - R at B-max. Optical spectra share many similarities, but lower mass models exhibit less UV line blanketing during the photospheric phase. At nebular times, significant near-infrared (NIR) spectroscopic differences are seen. In particular, emission lines of the Ca II NIR triplet; [S III] lambda lambda 9068,9530; [Ca II] lambda lambda 7291,7324; [Ar III] lambda lambda 7135,7751 and [Ni II] 1.939 mu m are stronger in higher mass models. The [Ni II] 1.939 mu m line is absent in the sub-M-Ch detonation model, and provides a valuable potential tool to distinguish sub-M-Ch explosions from M-Ch explosions. In general, the nebular phase models are too highly ionized. We attribute this to the neglect of clumping and/or the distribution of intermediate mass and iron group elements. The two sub-M-Ch models, while exploded by different mechanisms, can be distinguished in the J and H bands at late times (e.g. +200 d).