# Minor merger growth in action: JWST detects faint blue companions around massive quiescent galaxies at 0.5 < z < 3

**Authors:** Katherine A. Suess, Christina C. Williams, Brant Robertson, Zhiyuan Ji, Benjamin D. Johnson, Erica Nelson, Stacey Alberts, Kevin Hainline, Francesco DEugenio, Hannah Ubler, Marcia Rieke, George Rieke, Andrew J. Bunker, Stefano Carniani, Stephane Charlot, Daniel J. Eisenstein, Roberto Maiolino, Daniel P. Stark, Sandro Tacchella, Chris Willott  
**arXiv:** [2307.14209](https://arxiv.org/abs/2307.14209)  
**Date:** 2023-07-26  
**Summary page:** https://www.summarizepaper.com/en/paper/2307.14209v1/

## Key points

- Researchers have discovered a large population of low-mass companions near massive quiescent galaxies
- Previous observations using HST were primarily sensitive to stellar mass ratios greater than 1:10
- New observations from JWST reveal that these low-mass companions are more common than previously thought
- Study focused on known quiescent galaxies with stellar mass > 10.5 times that of the Sun, located within 35 kpc and at redshifts between 0.5 and 3
- Massive companions similar to those identified by HST were rare, but average massive quiescent galaxy hosts around five nearby companions with stellar mass ratios less than 1:10
- Tiny companions contribute significantly to total mass through minor mergers, accounting for at least 30% of total mass growth
- Low-mass companions tend to have bluer colors and lower mass-to-light ratios compared to host galaxies at similar radii
- Accretion of low-mass companions likely drives changes in color gradients and stellar population properties of host galaxies
- Minor merger growth extends down to very low mass ratios of less than 1:100
- JWST provides detailed observations of both massive galaxies and their low-mass companions beyond our local universe
- JWST has expanded our understanding of how minor mergers contribute to the structural evolution and growth of massive quiescent galaxies

## Summary

In a recent study, researchers have discovered a large population of low-mass companions near massive quiescent galaxies. Previous observations using the Hubble Space Telescope (HST) were primarily sensitive to stellar mass ratios greater than 1:10. However, the new observations from the James Webb Space Telescope (JWST) reveal that these low-mass companions are more common than previously thought. The study focused on known quiescent galaxies with a stellar mass greater than 10.5 times that of the Sun, located within 35 kiloparsecs (kpc) and at redshifts between 0.5 and 3. The researchers found that while massive companions similar to those identified by HST were rare, the average massive quiescent galaxy hosts around five nearby companions with stellar mass ratios less than 1:10. Despite their small size, these tiny companions contribute significantly to the total mass being added through minor mergers, accounting for at least 30% of the total mass growth. Moreover, these low-mass companions tend to have bluer colors and lower mass-to-light ratios compared to their host galaxies at similar radii. This suggests that accretion of these low-mass companions is likely driving changes in the color gradients and stellar population properties of the host galaxies. The results indicate that minor merger growth extends down to very low mass ratios of less than 1:100. This study demonstrates the power of JWST in providing detailed observations of both massive galaxies and their low-mass companions beyond our local universe. By revealing this previously unknown population of faint blue companions, JWST has expanded our understanding of how minor mergers contribute to the structural evolution and growth of massive quiescent galaxies.