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 × 109μ-1K km s-1pc-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 derived a mass flow rate of molecular gas in the range ? = 3-7.4 × 103M⊙/yr and momentum boost ?OF/?AGN∼ 2-6, which is therefore consistent with a momentum conserving flow. For the largest ?OFthe scaling is also consistent with an 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 = ?OF/SFR is ? 1. We also detected a molecular emission line at a frequency of 94.83 GHz corresponding to a rest-frame frequency of 465.8 GHz; we tentatively identified this frequency 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.