Is Dust Continuum Emission a Good Gas Tracer in Pre-Stellar Cores? Aurore Bacmann IPAG, Grenoble, FR
Accurate knowledge of mass and its distribution in prestellar cores is of capital importance to understand how star formation proceeds in its first stages and to determine the core mass function. Dust continuum emission is the most widely used method to derive the mass distribution, especially now that the Herschel Space Observatory has allowed us to map with unprecedented sensitivity and speed very large areas in star forming regions. However, this method suffers from uncertainties in the dust properties, which are not well quantified. Deriving mass from the gas is an appealing alternative because it does not suffer from such large uncertainties, provided the gas tracer is not strongly depleted at high densities. The ions N2H+ and N2D+ are therefore particularly interesting in this respect. In this contribution, we present a method based on the modelling of multitransition N2H+ maps, using a 1D radiative transfer code. This enables us to determine simultaneously the gas density distribution, gas temperature as well as the molecular abundance profiles. We find that the density profile derived from the gas and that derived from dust continuum emission in the same source are not consistent. We discuss the origins of the discrepancies and consequences.
Collaborators: L. Pagani, LERMA, FR C. Favre, AAO, IT	Suggested Session: Cores