Two Physically Distinct Populations of Low-Ionization Nuclear Emission-Line Regions

TL;DR

This study identifies two distinct populations of LINERs with different spectral, infrared, and supernova properties, indicating they have different excitation mechanisms and evolutionary stages.

Contribution

The paper reveals that LINERs are divided into two categories with distinct properties and likely different origins, based on spectral analysis and multi-wavelength observations.

Findings

Population I LINERs have broad emission lines.

Population II LINERs show luminous infrared emission.

The two populations differ in their excitation mechanisms and evolutionary stages.

Abstract

The nature of Low-ionization Nuclear Emission-line Regions (LINERs) has been an open question for a long time. We study the properties of LINERs from several different aspects. The LINERs are found to consist of two different categories that can be clearly separated in the traditional BPT diagrams, especially in the [OI]/Ha vs. [OIII]/Hb diagram. LINERs with high [O]/Ha ratios (population I) differ from ones with low ratios (population II) in several properties. Broad emission lines are only identified in the spectra of population I LINERs. While only the population II LINERs show luminous infrared emission and occurrence of core-collapse supernovae in the host. Combining these results with the known distribution of stellar populations not only suggests that the two populations have different line excitation mechanisms, but also implies that they are at different evolutionary stages.