2011ApJ...743..194C

The high-mass star-forming clump W43-MM1 has been mapped in N₂H⁺(4 ⟶ 3), C¹⁸O(3 ⟶ 2), SiO(8 ⟶ 7), and in a single pointing in DCO⁺(5 ⟶ 4) toward the center of the clump. Column densities from these observations as well as previous HCO⁺(4 ⟶ 3), H¹³CO⁺(4 ⟶ 3), HCN(4 ⟶ 3), H¹³CN(4 ⟶ 3), and CS(7 ⟶ 6) data have been derived using the RADEX code; results later have been used to derive chemical abundances at selected points in the MM1 main axis. We compare with chemical models to estimate an evolutionary age of 10⁴ years for a remarkable warm hot core inside MM1. We also proposed that the dust temperature derived from the spectral energy distribution fitting in MM1 is not representative of the gas temperature deep inside the clump because dust emission may have become optically thick. By deriving a deuterium fractionation of 1.2x10³, we estimate an electron fraction of X(e) = 6.5x10^–8. Thus, the coupling between the neutral gas and the magnetic field is estimated by computing the ambipolar diffusion Reynolds number R_m= 18 and the wave coupling number W = 110. Considering that the infalling speed is slightly supersonic (M = 1.1) but sub-Alfvénic, we conclude that the MM1 clump has recently been or is in the process of decoupling the field from the neutral fluid. Thus, the MM1 clump appears to be in an intermediate stage of evolution in which a hot core has developed while the envelope is still infalling and not fully decoupled from the ambient magnetic field.