The SAGA Survey. III. A Census of 101 Satellite Systems around Milky Way-mass Galaxies

TL;DR

The SAGA Survey's third data release provides a comprehensive spectroscopic census of 378 satellite galaxies around 101 Milky Way-mass hosts, revealing diversity in satellite properties and distributions, and offering insights into galaxy formation and satellite dynamics.

Contribution

This work presents the largest, most complete spectroscopic survey of satellite galaxies around MW-mass hosts, including detailed completeness modeling and comparative analysis with the Milky Way.

Findings

Satellite abundance correlates with the mass of the most massive satellite.

One-third of systems contain LMC-mass satellites, often with more satellites than the MW.

Satellite radial distribution is less concentrated than in the MW.

Abstract

We present Data Release 3 (DR3) of the Satellites Around Galactic Analogs (SAGA) Survey, a spectroscopic survey characterizing satellite galaxies around Milky Way (MW)-mass galaxies. The SAGA Survey DR3 includes 378 satellites identified across 101 MW-mass systems in the distance range of 25-40.75 Mpc, and an accompanying redshift catalog of background galaxies (including about 46,000 taken by SAGA) in the SAGA footprint of 84.7 sq. deg. The number of confirmed satellites per system ranges from zero to 13, in the stellar mass range of 10^6 to 10^10 solar masses. Based on a detailed completeness model, this sample accounts for 94% of the true satellite population down to a stellar mass of 10^7.5 solar masses. We find that the mass of the most massive satellite in SAGA systems is the strongest predictor of satellite abundance; one-third of the SAGA systems contain LMC-mass satellites, and they tend to have more satellites than the MW. The SAGA satellite radial distribution is less concentrated than the MW's, and the SAGA quenched fraction below 10^8.5 solar masses is lower than the MW's, but in both cases, the MW is within 1 sigma of SAGA system-to-system scatter. SAGA satellites do not exhibit a clear corotating signal as has been suggested in the MW/M31 satellite systems. Although the MW differs in many respects from the typical SAGA system, these differences can be reconciled if the MW is an older, slightly less massive host with a recently accreted LMC/SMC system.