Distinguishing Active Galactic Nuclei and Star Formation

TL;DR

This paper presents a new empirical classification scheme for emission-line galaxies from SDSS data, clearly separating star-forming galaxies, Seyferts, and LINERs, and explores their host properties and evolutionary links.

Contribution

It introduces a novel classification method based on optical emission lines that improves separation of galaxy types and models their emission line distributions.

Findings

Clear separation of galaxy classes on diagnostic diagrams

Identification of host galaxy property differences

Models explaining galaxy distribution on emission line diagrams

Abstract

Using the large emission line galaxy sample from the Sloan Digital Sky Survey we show that Star forming galaxies, Seyferts, and low-ionization nuclear emission-line regions (LINERs) form clearly separated branches on the standard optical diagnostic diagrams. We derive a new empirical classification scheme which cleanly separates these emission-line galaxies, using strong optical emission lines. Using this classification we identify a few distinguishing host galaxy properties of each class, which, along with the emission line analysis, suggest continuous evolution from one class to another. As a final note, we introduce models of both Starforming galaxies and AGN narrow line regions which can explain the distribution of galaxies on standard emission line ratio diagrams, and possibly suggest new diagnostics across the emission spectrum.