The SAMI Galaxy Survey: Global stellar populations on the size-mass plane

TL;DR

This study analyzes the stellar populations of 1319 galaxies across various sizes, masses, and environments, revealing systematic variations linked to galaxy size, density, morphology, and environment.

Contribution

It provides a comprehensive analysis of how stellar populations vary across the size-mass plane, incorporating all morphologies and environments, and identifies key correlations and evolutionary trends.

Findings

Galaxies with higher surface mass density are older, more metal-rich, and alpha-enhanced.

Metallicity spread increases with galaxy size at fixed mass.

Residual effects of morphology and environment influence stellar populations.

Abstract

We present an analysis of the global stellar populations of galaxies in the SAMI Galaxy Survey. Our sample consists of 1319 galaxies spanning four orders of magnitude in stellar mass and includes all morphologies and environments. We derive luminosity-weighted, single stellar population equivalent stellar ages, metallicities and alpha enhancements from spectra integrated within one effective radius apertures. Variations in galaxy size explain the majority of the scatter in the age--mass and metallicity--mass relations. Stellar populations vary systematically in the plane of galaxy size and stellar mass, such that galaxies with high stellar surface mass density are older, more metal-rich and alpha-enhanced than less dense galaxies. Galaxies with high surface mass densities have a very narrow range of metallicities, however, at fixed mass, the spread in metallicity increases substantially with increasing galaxy size (decreasing density). We identify residual correlations with morphology and environment. At fixed mass and size, galaxies with late-type morphologies, small bulges and low Sersic n are younger than early-type, high n, high bulge-to-total galaxies. Age and metallicity both show small residual correlations with environment; at fixed mass and size, galaxies in denser environments or more massive halos are older and somewhat more metal rich than those in less dense environments. We connect these trends to evolutionary tracks within the size--mass plane.