科研之友
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摘要
We present near-IR spectroscopy of 22 luminous low-ionization broad absorption line quasars (LoBAL QSOs) at redshift 1.3 < z < 2.5, with 12 objects at z similar to 1.5 and 10 at z similar to 2.3. The spectra cover the rest-frame H alpha and H beta line regions, allowing us to obtain robust black hole mass estimates based on the broad H alpha line. We use these data, augmented by a lower-redshift sample from the Sloan Digital Sky Survey, to test the proposed youth scenario for LoBALs, which suggests that LoBALs constitute an early short-lived evolutionary stage of quasar activity, by probing for any difference in their masses, Eddington ratios, or rest-frame optical spectroscopic properties compared to normal quasars. In addition, we construct the UV to mid-IR spectral energy distributions (SEDs) for the LoBAL sample and a matched non-BAL quasar sample. We do not find any statistically significant difference between LoBAL QSOs and non-BAL QSOs in their black hole mass or Eddington ratio distributions. The mean UV to mid-IR SED of the LoBAL QSOs is consistent with non-BAL QSOs, apart from their stronger reddening. At z > 1 there is no clear difference in their optical emission line properties. We do not see particularly weak [O III] or strong Fe II emission. The LoBAL QSOs do not show a stronger prevalence of ionized gas outflows as traced by the [O III] line, compared to normal QSOs of similar luminosity. We conclude that the optical-MIR properties of LoBAL QSOs are consistent with the general quasar population and do not support them to constitute a special phase of active galactic nucleus evolution.
- 出版日期2017-10-20
- 单位中国科学院国家天文台; 中国科学院上海天文台; 北京大学
