2012ApJ...753...34J

We present high angular resolution observations (0".5x0".3) carried out with the Submillimeter Array (SMA) toward the AFGL2591 high-mass star-forming region. Our SMA images reveal a clear chemical segregation within the AFGL2591 VLA 3 hot core, where different molecular species (Types I, II, and III) appear distributed in three concentric shells. This is the first time that such a chemical segregation is ever reported at linear scales ≤ 3000 AU within a hot core. While Type I species (H₂ S and ¹³CS) peak at the AFGL2591 VLA 3 protostar, Type II molecules (HC₃N, OCS, SO, and SO₂) show a double-peaked structure circumventing the continuum peak. Type III species, represented by CH₃OH, form a ring-like structure surrounding the continuum emission. The excitation temperatures of SO₂, HC₃N, and CH₃ OH (185±11 K, 150 ±20 K, and 124±12 K, respectively) show a temperature gradient within the AFGL2591 VLA 3 envelope, consistent with previous observations and modeling of the source. By combining the H₂S, SO₂, and CH₃ OH images, representative of the three concentric shells, we find that the global kinematics of the molecular gas follow Keplerian-like rotation around a 40 M_☉star. The chemical segregation observed toward AFGL2591 VLA 3 is explained by the combination of molecular UV photodissociation and a high-temperature (∼1000 K) gas-phase chemistry within the low extinction innermost region in the AFGL2591 VLA 3 hot core.