SF-09-0004

The turbulent chemistry of a molecular cloud

Leire Beitia-Antero

The turbulent nature of the interstellar medium (ISM) has been put forward many times as a possible explanation for the mismatch between theoretical predictions and observations. In this contribution, we present the results of a theoretical study in which we explore to what extent this turbulence may cause chemical inhomogeneities inside a dense molecular cloud before collapse, and if this turbulence alone can explain the observationally-derived abundances of a series of molecules commonly observed in the ISM. We perform a series of numerical MHD simulations of isothermal turbulent boxes with trans-sonic turbulence to reproduce the turbulent steady-state of a molecular cloud, and then post-process the results with a chemical grid to predict the abundances of some molecules (CO, HCO+, CS, SO, OCS, HCN, HNC, H2S, HCS+). These abundances, together with the velocity field provided by the simulations, are then used as an input for a radiative transfer code in order to predict the line intensities for some rotational transitions that can be observed with the IRAM 30m telescope; this post-processing is performed for several relative alignments between the observer and the mean magnetic field direction, and under two assumptions: that the medium is uniform along the line of sight, as assumed when fitting observations, and that the density distribution is given by the turbulent box simulations. We find that some transitions are very sensitive to the assumption of gas distribution along the line of sight, resulting in integrated line intensities twice larger than for the uniform case; on the other hand, the magnetic field alignment only affects the line profiles, producing a broadening of the lines for the perpendicular case that can be detected even after convolution with the telescope beam.