Strong [O III] Objects Among SDSS Broad-Line Active Galaxies

TL;DR

This study uses spectral principal component analysis on over 9,000 SDSS broad-line AGN to explore spectral correlations and the impact of [O III] strength variations, revealing complex relationships influenced by covering factor variations.

Contribution

It applies spectral PCA to a large AGN sample to analyze spectral correlations and the effects of [O III] strength, highlighting the role of covering factor variations.

Findings

Correlations between spectral regions are confirmed through spectral measurements.

Known relationships between [O III] strength, Hβ width, and Fe II are recovered only in the weakest [O III] subset.

Wide [O III] equivalent width range complicates principal component interpretation.

Abstract

We present the results of a spectral principal component analysis on 9046 broad-line AGN from the Sloan Digital Sky Survey. We examine correlations between spectral regions within various eigenspectra (e.g., between Fe II strength and H$\beta$ width) and confirm that the same trends are apparent in spectral measurements, as validation of our technique. Because we found that our sample had a large range in the equivalent width of [O III] $\lambda$5007, we divided the data into three subsets based on [O III] strength. Of these, only in the sample with the weakest equivalent width of [O III] were we able to recover the known correlation between [O III] strength and full width at half maximum of H$\beta$ and their anticorrelation with Fe II strength. At the low luminosities considered here ($L_{5100 \AA}$ of $10^{42}-10^{46}$ erg s$^{-1}$), interpretation of the principal components is considerably complicated particularly because of the wide range in [O III] equivalent width. We speculate that variations in covering factor are responsible for this wide range in [O III] strength.