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.