Chemical and physical picture of IRAS 16293-2422 source b at a sub-arcsecond scale studied with ALMA

We have analyzed the OCS, H₂CS, CH₃OH, and HCOOCH₃data observed toward the low-mass protostar IRAS 16293-2422 Source B at a sub-arcsecond resolution with ALMA. A clear chemical differentiation is seen in their distributions; OCS and H₂CS are extended with a slight rotation signature, while CH₃OH and HCOOCH₃are concentrated near the protostar. Such a chemical change in the vicinity of the protostar is similar to the companion (Source A) case. The extended component is interpreted by the infalling-rotating envelope model with a nearly face-on configuration. The radius of the centrifugal barrier of the infalling-rotating envelope is roughly evaluated to be (30 - 50) au. The observed lines show the inverse P-Cygni profile, indicating the infall motion with in a few 10 au from the protostar. The nearly pole-on geometry of the outow lobes is inferred from the SiO distribution, and thus, the infalling and outowing motions should coexist along the line-of-sight to the protostar. This implies that the infalling gas is localized near the protostar and the current launching points of the outow have an offset from the protostar. A possible mechanism for this configuration is discussed.