PROPERTIES OF INTERSTELLAR MEDIUM IN INFRARED-BRIGHT QSOs PROBED BY [O i] 63 μm AND [C ii] 158 μm EMISSION LINES*

Abstract

We present a study of the interstellar medium (ISM) in the host galaxies of nine QSOs at 0.1 < z < 0.2 with black hole masses of to based on the far-IR spectroscopy taken with Herschel Space Observatory . We detect the [O i ] 63 μ m ([C ii ] 158 μ m) emission in 6 (8) out of 8 (9) sources. Our QSO sample has far-infrared luminosities ( ) ∼ several times . The observed line-to- ratios ( / and / ) are in the ranges of 2.6 × 10 −4 to 10 −2 and 2.8 × 10 −4 to 2 × 10 −3 , respectively (including upper limits). These ratios are comparable to the values found in local ULIRGs, but higher than the average value published so far for IR-bright QSOs. One target, W0752+19, shows an additional broad velocity component (∼720 km s −1 ) and exceptionally strong [O i ] 63 μ m emission with / of 10 −2 , an order of magnitude higher than the average value found among local (U)LIRGs. Combining with the analyses of the Sloan Digital Sky Survey optical spectra, we conclude that the [O i ] 63 μ m emission in these QSOs is unlikely excited by shocks. We infer that the broad [O i ] 63 μ m emission in W0752+19 could arise from the warm and dense ISM in the narrow-line region of the central active galactic nucleus. Another possible explanation is the existence of a dense gas outflow with cm −3 , where the corresponding broad [C ii ] emission is suppressed. Based on the far-IR [O i ] and [C ii ] line ratios, we estimate constraints on the ISM density and UV radiation field intensity of cm −3 and , respectively. These values are consistent with those found in local Seyfert 1 ULIRGs. In contrast, the gas with broad velocity width in W0752+19 has cm −3 and .