Low Luminosity AGN candidates in SDSS

TL;DR

This study identifies low luminosity AGN candidates in SDSS galaxies, revealing their properties, host types, and star formation histories, with many classified as LLAGN based on emission line analysis.

Contribution

It introduces a method to identify LLAGN candidates in SDSS data using emission line diagnostics and characterizes their properties and host galaxy types.

Findings

22% of NELGs lack key emission lines

Most are classified as LLAGN based on line widths and luminosities

Hosts are early-type galaxies with no recent star formation

Abstract

In a sample of 476931 NELGs obtained from the SDSS DR5 data we find that in 22% of the galaxies the emission line [OIII]$\lambda$5007, H$\beta$, or both, are missing. The nature of the activity in these galaxies was determined using a diagnostic diagram comparing the equivalent width of [NII]$\lambda$6584 with the ratio [NII]$\lambda$6584/H$\alpha$. The majority of these galaxies are AGN. The H$\alpha$ emission lines have a mean FWHM of 400 km s$^{-1}$ and mean luminosity of 5.6$\times$10$^{39}$ erg s$^{-1}$, which justify their classification as LLAGN. A study of their star formation histories using STARLIGHT reveals no trace of star formation over the last Gyr period. The hosts of the LLAGNs are early-type, T$\le 2$, with bulges more massive than those of the luminous AGNs.