Si and Ca high-velocity features in SNe Ia

Multiple Gaussian fits are applied to examine the HVFs and their evolutions, using constraints on expansion velocities for the same species (i.e., SiII5972 and SiII6355). We find that strong HVFs tend to appear in SNe Ia with smaller decline rates (e.g., {Delta}m_15_(B)<~1.4mag), clarifying that the finding by Childress et al. (2014MNRAS.437..338C) for the Ca-HVFs in near-maximum-light spectra applies both to the Si-HVFs and Ca-HVFs in the earlier phase.

The Si-HVFs seem to be more common in rapidly expanding SNe Ia, which is different from the earlier result that Ca-HVFs are associated with SNe Ia that have slower SiII6355 velocities at maximum light (i.e., V^Si^_max_). Moreover, SNe Ia with both stronger HVFs at early phases and larger V^Si^_max_ are found to have noticeably redder B-V colors and to occur preferentially in the inner regions of their host galaxies, while those with stronger HVFs but smaller V^Si^_max_ show opposite tendencies, suggesting that these two subclasses have different explosion environments and their HVFs may have different origins.