A Physical Basis for the H-band Blue-edge Velocity and Light-curve Shape Correlation in Context of Type Ia Supernova Explosion Physics

Our recent work demonstrates a correlation between the high-velocity blue edge, v(ed)(ge), of the iron-peak Fe/Co/Ni H-band emission feature and the optical light-curve (LC) shape of normal, transitional and subluminous SNe Ia. We explain this correlation in terms of SN Ia physics. V-edge corresponds to the sharp transition between the complete and incomplete silicon burning regions in the ejecta. It measures the point in velocity space where the outer Ni-56 mass fraction, X-Ni, falls to the order of 0.03-0.10. For a given Ni-56 mass, M(Ni-56), V-edge is sensitive to the specific kinetic energy E-kin(M(Ni-56)/M-WD) of the corresponding region. Combining V(edge )with LC parameters (i.e., s(BV), Delta m(15)(,s) . in B and V) allows us to distinguish between explosion scenarios. The correlation between V-edge and light-curve shape is consistent with explosion models near the Chandrasekhar limit. However, the available sub-M-Ch WD explosion model based on SN 1999by exhibits velocities that are too large to explain the observations. Finally, the subluminous SN 2015bo exhibits signatures of a dynamical merger of two WDs demonstrating diversity among explosion scenarios at the faint end of the SNe Ia population.