[O iii] 5007 Å Emission Line Width as a Surrogate for σ _∗ in Type 1 AGNs?

Abstract

We present a study of the relation between the [O iii] 5007 Å emission line width (σ [OIII]) and stellar velocity dispersion (σ *), utilizing a sample of 740 type 1 active galactic nuclei (AGNs) with high-quality spectra at redshift z < 1.0. We find the broad correlation between the core component of the [O iii] emission line width ( σ [ O III , core ] ) and σ * with a scatter of 0.11 dex for the low redshift (z < 0.1) sample; for redshift (0.3 < z < 1.0) AGNs, the scatter is larger, being 0.16 dex. We also find that the Eddington ratio (L bol/L Edd) may play an important role in the discrepancies between σ [ O III , core ] and σ *. As the L bol/L Edd increases, σ [ O III , core ] tends to be larger than σ *. By classifying our local sample with different minor-to-major axis ratios, we find that σ * is larger than σ [ O III , core ] for those edge-on spiral galaxies. In addition, we also find that the effects of outflow strength properties such as maximum outflow velocity ( V max ) and the broader component of the [O iii] emission line width and line shift (σ [OIII,out] and V [OIII,out]) may play a major role in the discrepancies between σ [ O III , core ] and σ *. The discrepancies between σ [ O III , core ] and σ * are larger when V max , V [OIII,out], and σ [OIII,out] increase. Our results show that the outflow strengths may have significant effects on the differences between narrow-line region gas and stellar kinematics in AGNs. We suggest that caution should be taken when using σ [ O III , core ] as a surrogate for σ *. In addition, the substitute of σ [ O III , core ] for σ * could be used only for low luminosity AGNs.