Water and methanol in low-mass protostellar outflows: gas-phase synthesis, ice sputtering and destruction

Water in outflows from protostars originates either as a result of gas-phase synthesis from atomic oxygen at T ≳ 200 K, or from sputtered ice mantles containing water ice. We aim to quantify the contribution of the two mechanisms that lead to water in outflows, by comparing observations of gas-phase water to methanol (a grain surface product) towards three low-mass protostars in NGC 1333. In doing so, we also quantify the amount of methanol destroyed in outflows. To do this, we make use of James Clerk Maxwell Telescope and Herschel -Heterodyne Instrument for the Far-Infrared data of H 2 O, CH 3 OH and CO emission lines and compare them to RADEX non-local thermodynamic equilibrium excitation simulations. We find up to one order of magnitude decrease in the column density ratio of CH 3 OH over H 2 O as the velocity increases in the line wings up to ∼15 km s −1 . An independent decrease in X(CH 3 OH) with respect to CO of up to one order of magnitude is also found in these objects. We conclude that gas-phase formation of H 2 O must be active at high velocities (above 10 km s −1 relative to the source velocity) to re-form the water destroyed during sputtering. In addition, the transition from sputtered water at low velocities to form water at high velocities must be gradual. We place an upper limit of two orders of magnitude on the destruction of methanol by sputtering effects.