# The SAGA Survey. IV. The Star Formation Properties of 101 Satellite Systems around Milky Way-mass Galaxies

**Authors:** Marla Geha, Yao-Yuan Mao, Risa H. Wechsler, Yasmeen Asali, Erin Kado-Fong, Nitya Kallivayalil, Ethan O. Nadler, Erik J. Tollerud, Benjamin Weiner, Mithi A. C. de los Reyes, Yunchong Wang, John F. Wu  
**arXiv:** [2404.14499](https://arxiv.org/abs/2404.14499)  
**Date:** 2024-04-22  
**Summary page:** https://www.summarizepaper.com/en/paper/2404.14499v1/

## Key points

- The SAGA Survey examines star-forming properties of 378 satellite galaxies around 101 Milky Way analogs
- Factors analyzed within stellar mass range of 10^6 to 10^10 solar masses include quenched fractions, star-forming rates, gas-phase metallicities, and gas content
- Quenched fractions increase as stellar mass decreases, with highest proportions observed within central 100 kpc of host galaxies
- Least active quartile of satellites mirrors radial trend seen in overall quenched population based on specific star formation rate (sSFR)
- Star-forming satellites align with established star formation rate-stellar mass relationship but have higher median gas-phase metallicity and lower median HI gas mass across all stellar masses
- Host halo masses influence satellite quenching fractions, with higher quenched fractions in systems with greater host halo masses primarily within innermost 100 kpc region
- Systems neighboring a massive galaxy within 2.5 Mpc display elevated quenched fractions at all radii
- Lower-mass satellites and those located within 100 kpc from hosts are more effectively suppressed in Milky Way-like environments, but actively star-forming satellites still exist at varying stellar masses and distances

## Summary

The SAGA Survey explores the star-forming properties of 378 satellite galaxies surrounding 101 Milky Way analogs, shedding light on the environmental mechanisms that impact star formation. Within the stellar mass range of 10^6 to 10^10 solar masses, various factors such as quenched fractions, star-forming rates, gas-phase metallicities, and gas content are analyzed. Notably, the proportion of quenched SAGA satellites rises as stellar mass decreases, with considerable variation from system to system. The highest quenched fractions are observed within the central 100 kiloparsecs (kpc) of their host galaxies, gradually decreasing towards the virial radius. When categorized by specific star formation rate (sSFR), it is evident that the least active quartile of satellites mirrors the radial trend seen in the overall quenched population. Furthermore, while the median sSFR of star-forming satellites increases with diminishing stellar mass, it remains relatively stable across projected radii. Star-forming SAGA satellites align closely with the established star formation rate-stellar mass relationship in the Local Volume; however, they exhibit higher median gas-phase metallicity and lower median HI gas mass across all stellar masses. The study delves into how host properties influence satellite quenching fractions. Systems with greater host halo masses tend to have higher quenched fractions but primarily within the innermost 100 kpc region. Interestingly, systems neighboring a massive galaxy within a distance of 2.5 megaparsecs (Mpc) display elevated quenched fractions at all radii. These findings suggest that lower-mass satellites and those located within 100 kpc from their hosts are more effectively suppressed in a Milky Way-like environment. Despite this suppression, there remains a preserved cohort of actively star-forming satellites at varying stellar masses and projected distances—a testament to the intricate interplay between environmental processes and satellite galaxy evolution in galactic analogs like those studied in the SAGA Survey.