Stellar and gaseous velocity dispersions in type II AGNs at 0.3 <z< 0.83 from the Sloan Digital Sky Survey

Abstract

We apply the stellar population synthesis code by Cid Fernandes et al. to model the stellar contribution for a sample of 209 type II active galactic nuclei (AGNs) at 0.3 < z < 0.83 from the Sloan Digital Sky Survey. The reliable stellar velocity dispersions (σ*) are obtained for 33 type II AGNs with significant stellar absorption features. According to the L[O III] criterion of 3 × 108 L⊙, 20 of which can be classified as type II quasars. We use the formula of Greene and Ho to obtain the corrected stellar velocity dispersions (σc*). We also calculate the supermassive black hole masses from σc* in these high-redshift type II AGNs. The [O iii] luminosity is correlated with the black hole mass (although no correlation between the extinction-corrected [O iii] luminosity and the black hole mass), and no correlation is found between the Eddington ratio and the [O iii] luminosity or the corrected [O iii] luminosity. Three sets of two-component profiles are used to fit multiple emission transitions ([O iii]λλ4959, 5007 and [O ii]λλ3727, 3729) in these 33 stellar-light-subtracted spectra. We also measure the gas velocity dispersion (σg) from these multiple transitions, and find that the relation between σg and σc* becomes much weaker at higher redshifts than in smaller redshifts. The distribution of 〈σg/σc*〉 is 1.24 ± 0.76 for the core [O iii] line and 1.20 ± 0.96 for the [O ii] line, which suggests that σg of the core [O iii] and [O ii] lines can trace σc* within about 0.1 dex in the logarithm of σc*. For the secondary driver, we find that the deviation of σg from σc* is correlated with the Eddington ratio.