2016ApJ...820L..34S

Subarcsecond images of the rotational line emission of CS and SO have been obtained toward the Class I protostar IRAS 04365+2535 in TMC-1A with ALMA. A compact component around the protostar is clearly detected in the CS and SO emission. The velocity structure of the compact component of CS reveals infalling-rotating motion conserving the angular momentum. It is well explained by a ballistic model of an infalling-rotating envelope with the radius of the centrifugal barrier (one-half of the centrifugal radius) of 50 au, although the distribution of the infalling gas is asymmetric around the protostar. The distribution of SO is mostly concentrated around the radius of the centrifugal barrier of the simple model. Thus, a drastic change in chemical composition of the gas infalling onto the protostar is found to occur at a 50 au scale probably due to accretion shocks, demonstrating that the infalling material is significantly processed before being delivered into the disk.