Chemistry as a diagnostic of prestellar core geometry
The true 3D shapes of prestellar cores can provide useful insights about the initial conditions and the processes that regulate star formation. Unfortunately, two dimensional projections on the plane of the sky, probed by dust emission maps, can be identical for different intrinsic 3D core shapes. In lifting this shape degeneracy interstellar chemistry can be proven a useful ally. We present a simple but reliable method for assessing the intrinsic 3D shape of prestellar cores from molecular column densities. We have employed hydrodynamic simulations of contracting, isothermal cores considering three intrinsic geometries: spherical, cylindrical/filamentary and disk-like. We have coupled our hydrodynamic simulations with non-equilibrium chemical modelling. We then considered various orientations with respect to the line of sight. We have demonstrated that the true shape of the core can be identified by a metric that involves the column density profiles of pairs of commonly observed molecules or by a simple comparison of 2D emission maps of specific molecules. We have performed extensive parameter studies and established that our method is robust against the choice of free parameters associated with the interstellar chemistry.