Revealing components of the galaxy population through nonparametric techniques

TL;DR

This paper uses nonparametric techniques to identify four distinct components in galaxy populations based on H-alpha emission, revealing that these components are environment-independent but their proportions vary with environment.

Contribution

It introduces a novel nonparametric method to decompose galaxy populations into components, providing new insights into galaxy development processes.

Findings

Identified four galaxy components: passive, star-forming, and two active galactic nuclei types.

Components are consistent across environments, with only their proportions changing.

Galaxies transition rapidly between components as they move into denser environments.

Abstract

The distributions of galaxy properties vary with environment, and are often multimodal, suggesting that the galaxy population may be a combination of multiple components. The behaviour of these components versus environment holds details about the processes of galaxy development. To release this information we apply a novel, nonparametric statistical technique, identifying four components present in the distribution of galaxy H$\alpha$ emission-line equivalent-widths. We interpret these components as passive, star-forming, and two varieties of active galactic nuclei. Independent of this interpretation, the properties of each component are remarkably constant as a function of environment. Only their relative proportions display substantial variation. The galaxy population thus appears to comprise distinct components which are individually independent of environment, with galaxies rapidly transitioning between components as they move into denser environments.