[OIII] 5007A Emission Line Width as a Surrogate for stellar dispersion in Type 1 AGNs?
Abstract
We present a study of the relation between the [OIII] 5007A emission line width (sigma[OIII]) and stellar velocity dispersion (sigma*), 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 [OIII] emission line width (sigma[OIII,core]) and sigma* 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 (Lbol/LEdd) may play an important role in the discrepancies between sigma[OIII,core] and sigma*. As the Lbol/LEdd increases, sigma[OIII,core] tends to be larger than sigma*. By classifying our local sample with different minor-to-major axis ratios, we find that sigma* is larger than sigma[OIII,core] for those edge-on spiral galaxies. In addition, we also find that the effects of outflow strength properties such as maximum outflow velocity (Vmax) and the broader component of [OIII] emission line width and line shift (sigma[OIII,out] and V[OIII,out]) may play a major role in the discrepancies between sigma[OIII,core] and sigma*. The discrepancies between sigma[OIII,core] and sigma* are larger when Vmax, V[OIII,out], and sigma[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 sigma[OIII,core] as a surrogate for sigma*. In addition, the substitute of sigma[OIII,core] for sigma* could be used only for low luminosity AGNs.
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