Properties of Interstellar Medium In Infrared Bright QSOs Probed by [O
  I]63 micron and [C II]158 micron Emission Lines
  We present a study of interstellar medium in the host galaxies of 9 QSOs at
0.1<z<0.2 with blackhole masses of $3\times10^7\,M_\odot$ to
$3\times10^9\,M_\odot$ based on the far-IR spectroscopy taken with {\it
Herschel Space Observatory}. We detect the [OI]63$\mu$m ([CII]158$\mu$m)
emission in 6(8) out of 8(9) sources. Our QSO sample has far-infrared
luminosities (LFIR)~several times $10^{11}L_\odot$. The observed line-to-LFIR
ratios (LOI/LFIR and LCII/LFIR) are in the ranges of
$2.6\times10^{-4}$-$10^{-2}$ and $2.8\times10^{-4}$-$2\times10^{-3}$
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 $z$$>$1 IR bright QSOs. One target, W0752+19, shows an additional broad
velocity component (~720 km/s), and exceptionally strong [OI]63$\mu$m emission
with LOI/LFIR of $10^{-2}$, an order of magnitude higher than that of average
value found among local (U)LIRGs. Combining with the analyses of the {\it SDSS}
optical spectra, we conclude that the [OI]63$\mu$m emission in these QSOs is
unlikely excited by shocks. We infer that the broad [OI]63 micron emission in
W0752+19 could arise from the warm and dense ISM in the narrow line region of
the central AGN. Another possible explanation is the existence of a dense gas
outflow with $n_{\rm H}\sim10^4$\,cm$^{-3}$, where the corresponding broad
[CII] emission is suppressed. Based on the far-IR [OI] and [CII] line ratios,
we estimate the constraints on the ISM density and UV radiation field intensity
of $n_{\rm H} \lesssim 10^{3.3}$ cm$^{-3}$ and $10^3<G_0 \lesssim 10^{4.2}$,
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 $n_{\rm
H} \gtrsim 10^{4.3}$ cm$^{-3}$ and $G_0>10^4$.
