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 AGNs at $0.3<z<0.83$ from the Sloan Digital Sky Survey. The reliable stellar velocity dispersions ($\sigma_{*}$) are obtained for 33 type II AGNs with significant stellar absorption features. According to the $L_{\rm [O III]}$ criterion of $3\times 10^{8} \Lsolar$, 20 of which can be classified as type II quasars. We use the formula of Greene & Ho to obtain the corrected stellar velocity dispersions ($\sigma_{*}^c$). We also calculate the supermassive black holes masses from $\sigma_{*}^c$ 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 profile are used to fit multiple emission transitions ([O III]$\lambda\lambda$4959, 5007 and [O II]$\lambda\lambda$3727, 3729) in these 33 stellar-light subtracted spectra. We also measure the gas velocity dispersion ($\sigma_{g}$) from these multiple transitions, and find that the relation between $\sigma_{g}$ and $\sigma_{*}^c$ becomes much weaker at higher redshifts than in smaller redshifts. The distribution of $<\sigma_{g}/\sigma_{*}^c>$ is $1.24\pm0.76$ for the core [O III] line and $1.20\pm0.96$ for the [O II] line, which suggests that $\sigma_{g}$ of the core [O III] and [O II] lines can trace $\sigma_{*}^c$ within about 0.1 dex in the logarithm of $\sigma_{*}^c$. For the secondary driver, we find that the deviation of $\sigma_{g}$ from $\sigma_{*}^c$ is correlated with the Eddington ratio.