Abstract
Star formation processes such as infall, accretion, and outflows increase the complexity of molecules, allowing us to use those molecules to probe the physical environments where stars form. The most direct probe of infall is redshifted absorption against the central continuum source, which is best shown in dense gas tracers, such as HCO+ and HCN. Our ALMA observations of these two molecules show such redshifted absorption toward an isolated embedded protostar, BHR71. Both lines show a similar redshifted absorption profile, indicative of infall. Based on the previous model of BHR71 constrained by the Herschel observations, we model the line profiles with 3D radiative transfer calculations to constrain the infall kinematics. Together with a parameterized chemical abundance profile, we successfully reproduce the infall signature from the HCO+ line. We also found emissions of complex organic molecules (COMs), revealing the "hot corinos" nature of BHR71. We found that COMs emit from a compact region centered on the continuum source, corresponding to ~50 AU. Several COMs, such as methanol and methyl formate, show clear signatures of rotation, which is consistent with a ring from a part of rotating infalling envelope. We demonstrate an efficient observing strategy to simultaneously measure infall at both envelope and disk scales.
