# Environmental Dependence of Type Ia Supernovae in Low-Redshift Galaxy Clusters

**Authors:** Conor Larison, Saurabh W. Jha, Lindsey A. Kwok, Yssavo Camacho-Neves  
**arXiv:** [2306.01088](https://arxiv.org/abs/2306.01088)  
**Date:** 2023-06-01  
**Summary page:** https://www.summarizepaper.com/en/paper/2306.01088v1/

## Key points

- Analysis of 102 type Ia supernovae (SNe Ia) in nearby galaxy clusters
- Largest sample of its kind to date
- Based on archival data from ZTF and ATLAS
- SNe Ia divided into inner and outer cluster samples
- Inner cluster sample shows higher fraction of fast-evolving objects compared to outer cluster and field quiescent samples
- Bimodal distribution of SNe Ia with dominant presence of fast-evolving objects in inner clusters
- No significant variations observed in color distributions among different samples
- Minor differences found in SN Ia standardization parameters and Hubble residuals
- Age differences between stellar populations may drive observed distributions
- Environmental conditions within galaxy clusters play a crucial role in shaping properties of SNe Ia beyond host galaxy properties alone
- Valuable insights into environmental dependence of SNe Ia in low-redshift galaxy clusters

## Summary

In this study, the authors present an analysis of 102 type Ia supernovae (SNe Ia) in nearby galaxy clusters selected through x-ray observations. This dataset represents the largest sample of its kind to date and is primarily based on archival data from the Zwicky Transient Facility (ZTF) and Asteroid Terrestrial-impact Last Alert System (ATLAS). The SNe Ia are divided into two samples: an inner cluster sample projected within a radius of $r_{500}$ from the cluster center, and an outer cluster sample projected between $r_{500}$ and $2\,r_{500}$. These samples are then compared to field samples of SNe Ia at similar redshifts in both quiescent and star-forming host galaxies. By applying SALT3 fits to the light curves of these SNe Ia, the authors find that the inner cluster sample exhibits a higher fraction of fast-evolving objects (SALT3 $x_1 < -1$) compared to both the outer cluster and field quiescent samples. This suggests that there is an intrinsically different population of SNe Ia occurring in inner cluster environments which cannot be explained by known correlations based on host galaxy properties alone. Furthermore, the analysis reveals a strongly bimodal distribution of $x_1$ values for the cluster samples with a dominant presence of fast-evolving objects ($\gtrsim$ 75%) in inner clusters but only a small fraction ($\lesssim$ 10%) in field star-forming galaxies. However, no significant variations are observed in their color (SALT3 $c$) distributions among different samples. Additionally, minor differences are found in SN Ia standardization parameters and Hubble residuals. The authors propose that these observed distributions may be driven by age differences between stellar populations with older populations predominantly producing fast-evolving SNe Ia. This suggests that environmental conditions within galaxy clusters play a crucial role in shaping properties of SNe Ia beyond what can be attributed to host galaxy properties alone. Overall, this study provides valuable insights into environmental dependence of type Ia supernovae in low-redshift galaxy clusters. The large sample size and comprehensive analysis contribute to our understanding of diverse nature of SNe Ia and their connection to their host environments.