On the discovery of fast molecular gas in the UFO/BAL quasar APM
  08279+5255 at z=3.912
  We have performed a high sensitivity observation of the UFO/BAL quasar APM
08279+5255 at z=3.912 with NOEMA at 3.2 mm, aimed at detecting fast moving
molecular gas. We report the detection of blueshifted CO(4-3) with maximum
velocity (v95\%) of $-1340$ km s$^{-1}$, with respect to the systemic peak
emission, and a luminosity of $L' = 9.9\times 10^9 ~\mu^{-1}$ K km s$^{-1}$
pc$^{-2}$ (where $\mu$ is the lensing magnification factor). We discuss various
scenarios for the nature of this emission, and conclude that this is the first
detection of fast molecular gas at redshift $>3$. We derive a mass flow rate of
molecular gas in the range $\rm \dot M=3-7.4\times 10^3$ M$_\odot$/yr, and
momentum boost $\dot P_{OF} / \dot P_{AGN} \sim 2-6$, therefore consistent with
a momentum conserving flow. For the largest $\dot P_{OF}$ the scaling is also
consistent with a energy conserving flow with an efficiency of $\sim$10-20\%.
The present data can hardly discriminate between the two expansion modes. The
mass loading factor of the molecular outflow $\eta=\dot M_{OF}/SFR$ is $>>1$.
We also detect a molecular emission line at a frequency of 94.83 GHz,
corresponding to a rest frame frequency of 465.8 GHz, which we tentatively
identified with the cation molecule $\rm N_2H^+$(5-4), which would be the first
detection of this species at high redshift. We discuss the alternative
possibility that this emission is due to a CO emission line from the, so far
undetected, lens galaxy. Further observations of additional transitions of the
same species with NOEMA can discriminate between the two scenarios.
