Multi-line Herschel/HIFI observations of water reveal infall motions and chemical segregation around high-mass protostars

Context. The physical conditions during high-mass star formation are poorly understood. Outflow and infall motions have been detected around massive protostellar objects, but their dependence on mass, luminosity, and age is unclear. In addition, physical conditions and molecular abundances are often estimated using simple assumptions such as spherical shape and chemical homogeneity, which may limit the accuracy of the results. Aims: We aim to characterize the dust and gas distribution and kinematics of the envelopes of high-mass protostars. In particular, we search for infall motions, abundance variations, and deviations from spherical symmetry, using Herschel data from the WISH program. Methods: We used HIFI maps of the 987 GHz H2O 202-111 emission to measure the sizes and shapes of 19 high-mass protostellar envelopes. To identify infall, we used HIFI spectra of the optically thin C18O 9-8 and H218O 111-000 lines. The high-J C18O line traces the warm central material and redshifted H218O 111-000 absorption indicates material falling onto the warm core. We probe small-scale chemical differentiation by comparing H2O 752 and 987 GHz spectra with those of H218O. Results: Our measured radii of the central part of the H2O 202-111 emission are 30-40% larger than the predictions from spherical envelope models, and axis ratios are