The SAGA Survey IV

We measure star-formation rates, quenched fractions, gas-phase metallicities, and gas fractions for SAGA satellites around 101 MW-analog host galaxies. These quantities are determined from optical spectra, GALEX NUV images and HI survey data.

We define whether a given SAGA satellite is 'star-forming' or 'quenched' based on combined criteria in H-alpha and NUV-based star-formation rates.

SAGA satellites are preferentially quenched towards lower stellar masses. The Milky Way’s quenched fraction is a more extreme than SAGA, but is only a 1-sigma outlier from the SAGA average. The quenched fraction for the 18 SAGA hosts that are similar to the Local Group is indistinguishable from the full SAGA sample.

Quenched galaxies are more radially concentrated to their host galaxy compared to the star-forming satellites. Within the star-forming population, the least star-forming satellites are also more radially concentrated compared to the full star-forming population.

The SAGA sSFRs increase with decreasing stellar mass and are roughly constant with projected radius.

The median gas-phase metallicity of SAGA satellites is compared to galaxies in a wider range of environments. SAGA satellites have less HI gas compared to isolated galaxies at the same stellar mass. We also see secondary trends: at a given stellar mass, satellites with lower sSFR have lower than average gas fractions and higher gas-phase metallicity.

Gas-rich SAGA satellites (f_gas > 0.5) are observe at all projected distances from a host. Gas-poor systems lie preferentially inside of 100 kpc.  Satellites with the lowest gas fractions are more tightly bound to their host.

SAGA quenched fractions are higher in systems with more massive hosts, but higher quenched fractions are only seen in the inner 100 kpc. Systems with a massive neighbor within 2.5 Mpc show slightly higher quenched fractions at all radii.