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

**Authors:** Maria Pruzhinskaya, Aleksandra Novinskaya, Nicoleta Pauna, Philippe Rosnet  
**arXiv:** [2006.09433](https://arxiv.org/abs/2006.09433)  
**Date:** 2020-06-16  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2006.09433v1/

## Key points

- Type Ia Supernovae (SNe Ia) are used to measure distances in the Universe
- Intrinsic dispersion in the Hubble diagram may be due to environmental effects not yet accounted for
- A team of researchers studied the influence of host galaxy morphology on light-curve parameters of SNe Ia using the Pantheon cosmological supernova sample
- The team confirmed that the SALT2 stretch parameter $x_1$ depends on host morphology with a $p$-value of $\sim10^{-14}$
- Elliptical and lenticular galaxies mainly hosted supernovae with lower stretch values
- No correlation was found between the SALT2 color parameter $c$ and host morphology
- Early-type galaxies contained brighter supernovae than late-type galaxies due to their smaller mean distance modulus residuals
- There was no difference in residual dispersion between these two morphological groups
- Environmental dependence on SN Ia light-curve parameters and luminosity must be taken into account when refining our understanding of the Universe's expansion and evolution.

## Summary

Type Ia Supernovae (SNe Ia) are commonly used to measure distances in the Universe and have been improved by standardisation methods. However, there is still some intrinsic dispersion in the Hubble diagram which may be due to environmental effects not yet accounted for. To investigate this possibility, a team of researchers compared local and global color $(U-V)$, local star formation rate, host stellar mass and host galaxy morphology. They studied the influence of host galaxy morphology on light-curve parameters of SNe Ia using the Pantheon cosmological supernova sample and determined the Hubble morphological type of 330 SNe Ia hosts. The team confirmed that the SALT2 stretch parameter $x_1$ depends on host morphology with a $p$-value of $\sim10^{-14}$. Elliptical and lenticular galaxies mainly hosted supernovae with lower stretch values but no correlation was found between the SALT2 color parameter $c$ and host morphology. Additionally, they discovered that early-type galaxies contained brighter supernovae than late-type galaxies due to their smaller mean distance modulus residuals; however there was no difference in residual dispersion between these two morphological groups. These results demonstrate an environmental dependence on SN Ia light-curve parameters and luminosity which must be taken into account when refining our understanding of the Universe's expansion and evolution.