SIGNS OF EARLY-STAGE DISK GROWTH REVEALED WITH ALMA

Abstract

We present ALMA 1.3 mm continuum, 12 CO, C 18 O, 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 C 18 O, 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 C 18 O 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 C 18 O 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.