# Constraints on intragroup stellar mass from hostless Type Ia supernova

## TL;DR

This study uses hostless Type Ia supernovae to estimate the amount of diffuse stellar mass in galaxy groups, finding that stars constitute a small but significant fraction of the total group mass, challenging galaxy formation models.

## Contribution

It provides the first robust upper limit on diffuse stellar mass in galaxy groups using supernova data, revealing a higher proportion of diffuse light than previously estimated.

## Key findings

- Approximately 2.7% of group mass is in diffuse stars.
- About 47% of stellar mass in groups is in diffuse light.
- Stars account for roughly 3% of total group mass.

## Abstract

We probe the diffuse stellar mass in a sample of 1401 low redshift galaxy groups (10E13 - 10E14 Msun/h) by examining the rate of hostless Type Ia supernova (SNe Ia) within the groups. We correlate the sample of confirmed SNe Ia from the SDSS supernova survey with the positions of our galaxy groups, as well as with the resolved galaxies within them. We find that 19 of the 59 SNe Ia within the group sample have no detectable host galaxy, with another three ambiguous instances. This gives a robust upper limit that a maximum of 2.69% +1.58%/-1.34% of the group's total mass arises from diffuse stars in the intragroup medium. After correcting for a contribution from "prompt" SNe occurring within galaxies, and including a contribution from those which arise in dwarf galaxies below our photometric limit, we find that only 1.32% +0.78%/-0.70% of the group's total mass is likely in the form of diffuse stellar mass. Combining this result with the galaxy stellar mass functions of Yang et al., we find that 47% +16%/-15% of the stellar mass in our groups is in the form of diffuse light, so that stars make up a fraction 0.028 +0.011/-0.010 of the total group mass. Galaxy groups appear to be very efficient in disrupting stellar mass into a diffuse component; however, stars still make up a small fraction of the group mass, comparable to that seen in rich clusters. This remains a challenge to galaxy formation models.