title: Evidence for two distinct populations of type Ia supernovae.
abstract: Type Ia supernovae (SNe Ia) have been used as excellent standardizable candles for measuring cosmic expansion, but their progenitors are still elusive. Here, we report that the spectral diversity of SNe Ia is tied to their birthplace environments. We found that those with high-velocity ejecta are substantially more concentrated in the inner and brighter regions of their host galaxies than are normal-velocity SNe Ia. Furthermore, the former tend to inhabit larger and more luminous hosts. These results suggest that high-velocity SNe Ia likely originate from relatively younger and more metal-rich progenitors than do normal-velocity SNe Ia and are restricted to galaxies with substantial chemical evolution.
authors.affiliation: Department of Physics, Tsinghua University, Beijing, China. wang_xf@mail.tsinghua.edu.cn
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Wang
authors.forename: Lifan
authors.initials: L
authors.lastname: Wang
authors.forename: Alexei V
authors.initials: AV
authors.lastname: Filippenko
authors.forename: Tianmeng
authors.initials: T
authors.lastname: Zhang
authors.forename: Xulin
authors.initials: X
authors.lastname: Zhao