paper

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

arXiv:astro-ph/0608131 · doi:10.1111/j.1365-2966.2006.10915.x

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 ( $I ¨ _{*}$ ) are obtained for 33 type II AGNs with significant stellar absorption features. According to the $L_{[OIII]}$ 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 ( $I ¨ _{*}^{c}$ ). We also calculate the supermassive black holes masses from $I ¨ _{*}^{c}$ 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] $I^» I^»$ 4959, 5007 and [O II] $I^» I^»$ 3727, 3729) in these 33 stellar-light subtracted spectra. We also measure the gas velocity dispersion ( $I ¨ _{g}$ ) from these multiple transitions, and find that the relation between $I ¨ _{g}$ and $I ¨ _{*}^{c}$ becomes much weaker at higher redshifts than in smaller redshifts. The distribution of $< I ¨ _{g} / I ¨ _{*}^{c} >$ is $1.24 \pm 0.76$ for the core [O III] line and $1.20 \pm 0.96$ for the [O II] line, which suggests that $I ¨ _{g}$ of the core [O III] and [O II] lines can trace $I ¨ _{*}^{c}$ within about 0.1 dex in the logarithm of $I ¨ _{*}^{c}$ . For the secondary driver, we find that the deviation of $I ¨ _{g}$ from $I ¨ _{*}^{c}$ is correlated with the Eddington ratio.

7 figures, 1 table, accepted for publication in MNRAS