Yi-Shin Jheng (NCU); Yen-Chen Pan (NCU)
Type Ia Supernovae (SNe Ia) are exceptionally bright explosions, and their calibratable brightness make them powerful tools in probing the cosmic expansion. However, the progenitors of SNe Ia are still unclear. This could introduce uncertainties in their use in cosmology. Recent studies have shown that the ejecta velocity is an important variable in controlling SN Ia luminosities, even after the standard light-curve shape and color corrections have been performed. Theoretical studies also suggested that ejecta velocity could be promising in disentangling different SN Ia progenitor scenarios. In this work, we will measure the ejecta velocity from several absorptions lines in the optical spectra (e.g., Si II 6355 and Ca II H&K lines). We will use SNe Ia discovered by Pan-STARRS1 Medium Deep Survey (PS1 MDS) as our parent sample. Given that a large fraction of PS1 MDS SNe Ia are at high redshift (with a median redshift of ~0.3), their spectra are generally noisier than that of local sample. We will adopt a unique method to smooth these spectra and help us better determine the ejecta velocities of these SNe. In the future, we aim to investigate the relation between SN Ia ejecta velocities and other parameters, such as light-curve width, color and host parameters. Our high-redshift SN Ia sample will also allow us to study the potential evolution with the redshift, which is crucial for a high-precision cosmology.