Low Luminosity AGN candidates in SDSS

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.