出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We have selected a sample of 292 SDSS Narrow-Emission-Line galaxies (NELGs) known to have formed and evolved in relative isolation to study the nature and origin of the AGN phenomenon. The galaxies in our sample have line fluxes with S/N> 3 and were separated using a standard diagnostic diagram into Star Forming Galaxies (SFGs; 36.0%), Transition type Objects (TOs; 28.4%) and Narrow-Line AGNs (NLAGNs; 35.6%). Having found a strong correlation between the bulge mass and the NLAGN phenomenon, we have applied the same relation as for the Broad- Line AGNs (BLAGNs) to estimate their black hole (BH) masses. The BH in the NLAGNs are 2 to 3 orders lower in mass than the BHs found in BLAGNs, but are comparable to those observed in Narrow-Line Seyfert 1 (NLS1), although none of our objects can be classified as such. To determine the metallicities, [O/H], of the NLAGNs we calibrated the standard diagnostic diagram [OIII]/Hb vs. [NII]/Ha using similar relation as for the SFGs, which reproduce the values obtained with CLOUDY simulations developed for Bennert et al. [3]. For some individual objects we compared our line ratios with other CLOUDY similations by different authors. This suggests we achieve a typical uncertainty of 0.2 dex on [O/H], increasing to 0.3-0.5 in the Seyfert 2 (S2). This calibration suggests the metallicities of the NLAGNs are subsolar, varying between 1 and 0.3 Z . We find two statistically significant positive correlations: for [O/H] with the BH mass and for [O/H] with the luminosity at 5100Å, lL(5100Å). No correlation is found between [O/H] and the accretion rate, Lbol=LEdd. However, comparisons with the BLAGNs suggest the NLAGNs extend the metallicity-accretion rate relationship [24] to the low metallicity regime. Although the NLS1 have similar BH masses as the NLAGNs they show higher accretion rates, which is consistent with their higher metallicities.
