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 $L^{\mathrm{\prime }}=9.9\times {10}^9{\mu }^{-1}$ 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 $\dot{\mathrm{M}}=3-7.4\times {10}^3$ M${}_{\odot }$/yr, and momentum boost ${\dot{P}}_{OF}\mathrm{/}{\dot{P}}_{AGN}\sim 2-6$, 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 $\eta ={\dot{M}}_{OF}\mathrm{/}SFR$ 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 ${\mathrm{N}}_2{\mathrm{H}}^{+}$(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.