The dependency of Type Ia Supernova parameters on host galaxy morphology for the Pantheon cosmological sample

TL;DR

This study investigates how host galaxy morphology influences Type Ia Supernova parameters and their use in cosmology, revealing significant correlations that could improve supernova standardisation and reduce luminosity scatter.

Contribution

It demonstrates the dependence of SN Ia light-curve parameters on host galaxy morphology, emphasizing the importance of including host properties in supernova standardisation.

Findings

SN Ia stretch parameter $x_1$ depends on host morphology with high significance

Supernovae in early-type galaxies are brighter on average than those in late-type galaxies

No significant difference in residual dispersion between morphological groups

Abstract

Type Ia Supernovae (SNe Ia) are widely used to measure distances in the Universe. Despite the recent progress achieved in SN Ia standardisation, the Hubble diagram still shows some remaining intrinsic dispersion. The remaining scatter in supernova luminosity could be due to the environmental effects that are not yet accounted for by the current standardisation methods. In this work, we compare the local and global colour $(U-V)$, the local star formation rate, and the host stellar mass to the host galaxy morphology. The observed trends suggest that the host galaxy morphology is a good parameter to characterize the SN Ia environment. Therefore, we study the influence of host galaxy morphology on light-curve parameters of SNe Ia for the Pantheon cosmological supernova sample. We determine the Hubble morphological type of host galaxies for a sub-sample of 330 SNe Ia. We confirm that the SALT2 stretch parameter $x_1$ depends on the host morphology with the $p$-value $\sim10^{-14}$. The supernovae with lower stretch value are hosted mainly by elliptical and lenticular galaxies. No correlation for the SALT2 colour parameter $c$ is found. We also examine Hubble diagram residuals for supernovae hosted by the "Early-type" and "Late-type" morphological groups of galaxies. The analysis reveals that the mean distance modulus residual in early-type galaxies is smaller than the one in late-type galaxies, which means that early-type galaxies contain brighter supernovae. However, we do not observe any difference in the residual dispersion for these two morphological groups. The obtained results are in the line with other analyses showing environmental dependence of SN Ia light-curve parameters and luminosity. We confirm the importance of including a host galaxy parameter into the standardisation procedure of SNe Ia for further cosmological studies.