Resolved Neutral Outflow from a Lensed Dusty Star Forming Galaxy at z=2.09

We report the detection of a massive neutral gas outflow in the z=2.09 gravitationally lensed Dusty Star Forming Galaxy HATLASJ085358.9+015537 (G09v1.40), seen in absorption with the OH+(1_1-1_0) transition using spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations. The OH+ line, tracing diffuse atomic gas, is observed simultaneously with the CO(9-8) emission line and underlying dust continuum, providing kinematic and morphological information of the warm dense gas and dust in the host galaxy, respectively. Source plane reconstruction reveals a compact nuclear dust region from which the conical OH+ outflow emerges, away from the more extended and offset CO(9-8) and stellar distributions. The total atomic gas mass of the observed outflow is 6.7x10^9 M_sun>25 as massive as the molecular gas component within the galaxy. We derive outflow properties over a range of possible conical outflow inclinations (0.38 deg-64 deg), finding a neutral gas mass outflow rate between 83-25400 M_sun/yr, exceeding the star formation rate (788 M_sun/yr) if the inclination is >3.6 deg (mass-loading factor = 0.3-4.7). Kinetic energy and momentum fluxes are within 4.4-290x10^9 L_sun and 0.1-3.7x10^37 dyne, respectively (energy-loading factor = 0.013-16). If the inclination is small ( 12 deg, unusually high coupling efficiencies to the ISM, or an additional energy source (e.g. an active galactic nucleus), is needed.