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′=9.9×109μ−1 K km s−1
pc−2 (where μ 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 M˙=3−7.4×103 M⊙/yr, and
momentum boost P˙OF/P˙AGN∼2−6, therefore consistent with
a momentum conserving flow. For the largest P˙OF the scaling is also
consistent with a energy conserving flow with an efficiency of ∼10-20\%.
The present data can hardly discriminate between the two expansion modes. The
mass loading factor of the molecular outflow η=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 N2H+(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