# The SAGA Survey. V. Modeling Satellite Systems around Milky Way-mass Galaxies with Updated UniverseMachine

**Authors:** Yunchong Wang, Ethan O. Nadler, Yao-Yuan Mao, Risa H. Wechsler, Tom Abel, Peter Behroozi, Marla Geha, Yasmeen Asali, Mithi A. C. de los Reyes, Erin Kado-Fong, Nitya Kallivayalil, Erik J. Tollerud, Benjamin Weiner, John F. Wu  
**arXiv:** [2404.14500](https://arxiv.org/abs/2404.14500)  
**Date:** 2024-04-22  
**Summary page:** https://www.summarizepaper.com/en/paper/2404.14500v1/

## Key points

- Researchers Yunchong Wang, Ethan O. Nadler, Yao-Yuan Mao, Risa H. Wechsler, Tom Abel, Peter Behroozi, and Marla Geha focus on the role of environment in shaping low-mass galaxy assembly.
- The study utilizes the UniverseMachine (UM) framework and data from the Satellites Around Galactic Analogs (SAGA) Survey Data Release 3 to analyze dwarf galaxy star formation and quenching within a cosmological context.
- A new quenching model tailored for galaxies with stellar masses less than $10^9$ solar masses is incorporated into UM and constrained using observations from SAGA satellites around Milky Way-mass hosts and isolated field galaxies from SDSS.
- The resulting 'UM-SAGA' model successfully replicates key aspects observed in SAGA satellites while maintaining isolated dwarfs in a star-forming state.
- Higher levels of quenching are observed in satellites compared to isolated field galaxies, highlighting the importance of halo assembly processes in environmental quenching patterns.
- Projections indicate a significant difference in quenched fraction between isolated field galaxies and satellites orbiting MW-mass hosts at specific stellar mass ranges.
- The study suggests upcoming spectroscopic surveys can help validate predictions regarding internal feedback mechanisms, mass dynamics, gas processes, and reionization events influencing faint low-mass galaxy evolution.

## Summary

In the study titled "The SAGA Survey. V. Modeling Satellite Systems around Milky Way-mass Galaxies with Updated UniverseMachine," researchers Yunchong Wang, Ethan O. Nadler, Yao-Yuan Mao, Risa H. Wechsler, Tom Abel, Peter Behroozi, and Marla Geha delve into the critical role that environment plays in shaping the assembly of low-mass galaxies. By utilizing the UniverseMachine (UM) galaxy-halo connection framework and leveraging data from the Satellites Around Galactic Analogs (SAGA) Survey Data Release 3, the team places a particular focus on dwarf galaxy star formation and quenching within a cosmological context. The UM framework serves as a data-driven forward model that effectively parameterizes galaxy star formation rates (SFR) based solely on halo mass and assembly history. To enhance their analysis, a new quenching model tailored for galaxies with stellar masses less than approximately $10^9$ solar masses is incorporated into UM. This model is then constrained down to a stellar mass greater than approximately $10^7$ solar masses using fresh observations from SAGA of 101 satellite systems around Milky Way (MW)-mass hosts alongside a sample of isolated field galaxies within a similar mass range sourced from the Sloan Digital Sky Survey (SDSS). The resulting best-fit model dubbed 'UM-SAGA' successfully replicates key aspects such as satellite stellar mass functions, average SFRs, and quenched fractions observed in SAGA satellites while predominantly maintaining isolated dwarfs in a star-forming state. Notably, the heightened levels of quenching observed in satellites compared to isolated field galaxies prompt the model to heavily rely on halo assembly processes to account for environmental quenching patterns. By extrapolating the model to encompass stellar masses around $10^{6.5}$ solar masses, projections indicate a quenched fraction exceeding 30% for isolated field galaxies and surpassing 80% for satellites orbiting MW-mass hosts at this specific stellar mass range. This prediction presents an opportunity for validation through upcoming spectroscopic surveys aimed at elucidating the relative significance of internal feedback mechanisms, cessation of mass and gas accretion dynamics, satellite-specific gas processes, and reionization events in influencing the evolutionary trajectories of faint low-mass galaxies.