2023/10/09 by Chul Chung, Chung, Chul, Suk-Jin Yoon +11 · 3 citations
Physics and Astronomy · #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Gamma-ray bursts and supernovae
paper · pdf · doi:10.48550/arxiv.2310.06011
openalex publication_date 2023/10/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
It is well established that the Hubble residuals of type Ia supernovae (SNe Ia) show the luminosity step with respect to their host galaxy stellar masses. This `mass-step' is taken as an additional correction factor for the SN Ia luminosity standardization. Here we investigate the root cause of the mass-step and propose that the bimodal nature of the host age distribution is responsible for the step. In particular, by using the empirical nonlinear mass-to-age relation of local galaxies, we convert the mass function of SN Ia hosts to their age distribution. We find that the age distribution shows clear bimodality: a younger (< 6 Gyr) group with lower mass (∼ 109.5\rm M\rm sun) and an older (> 6 Gyr) group with higher mass (∼ 1010.5\rm M\rm sun). On the Hubble residual versus host mass plane, the two groups create the mass-step at ∼ 1010\rm M\rm sun. This leads us to conclude that the host galaxy mass-step can be attributed to the bimodal age distribution in relation to a nonlinear relation between galaxy mass and age. We suggest that the mass-step is another manifestation of the old `red sequence' and the young `blue cloud' observed in the galactic color--magnitude diagram.