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The standard model of prestellar core collapse suggests that this process works from the inside and moves outwards, with the fastest motions at the center. The relative abundances of many molecules also vary within cores, with certain molecules found only in specific regions characterized by narrow ranges of temperature and density. These characteristics lead to the hypothesis that the observed infall speeds in starless cores depend on both the position of the observations and the molecular tracer chosen. By measuring line emission at multiple positions across a core using an array of tracer molecules, one can determine whether these theoretical dependencies match observational evidence. Although surveys of infall motions in dense cores have been carried out for years, very few surveys have been awarded enough time to map infall across cores using multiple spectral line observations. To fill this gap, we present IRAM 30m maps of N2H (1-0), DCO(2-1), DCO(3-2) and HCO(3-2) emission towards two prestellar cores (L1544 and L694) and one protostellar core (L1521F). We find that the measured infall velocity varies as a function of position across each core and varies with the choice of molecular line, likely as a result of radial variations in core chemistry and dynamics. Subject headings: astronomy, astrophysics, star formation, dense cores, molecular clouds

Infall as a function of position and molecular tracer in dense cores.