2017ApJ...834..178Y

We present ALMA 1.3 mm continuum, ¹²CO, C¹⁸O, and SO data for the Class 0 protostars Lupus 3 MMS, IRAS 15398-3559, and IRAS 16253-2429 at resolutions of ∼100 au. By measuring a rotational profile in C¹⁸O, a 100 au Keplerian disk around a 0.3 M_☉ protostar is observed in Lupus 3 MMS. No 100 au Keplerian disks are observed in IRAS 15398-3559 and IRAS 16253-2429. Nevertheless, embedded compact (<30 au) continuum components are detected. The C¹⁸O emission in IRAS 15398-3559 shows signatures of infall with a constant angular momentum. IRAS 16253-2429 exhibits signatures of infall and rotation, but its rotational profile is unresolved. By fitting the C¹⁸O data with our kinematic models, the protostellar masses and the disk radii are inferred to be 0.01 M_☉ and 20 au in IRAS 15398-3559, and 0.03 M_☉ and 6 au in IRAS 16253-2429. By comparing the specific angular momentum profiles from 10,000 au to 100 au in eight Class 0 and I protostars, we find that the evolution of envelope rotation can be described with conventional inside-out collapse models. In comparison with a sample of 18 protostars with known disk radii, our results reveal signs of disk growth, with the disk radius increasing as M_*^0.8±0.14^ or t^1.09±0.37^ in the Class 0 stage, where M_* is the protostellar mass and t is the age. The disk growth rate slows down in the Class I stage. In addition, we find a hint that the mass accretion rate declines as t^-0.26±0.04^ from the Class 0 to the Class I stages.