Early Planet Formation in Embedded Disks (eDisk): picture of a protostar at the low mass end revealed in IRAS 16253-2429

Disk substructures in protoplanetary disks are considered to be signs of planet formation. Meanwhile, recent survey observations have pointed out that the typical protoplanetary disks are not massive enough to form giant planets, whereas numerous giant planets are found in extrasolar systems. These results imply planet formation in an earlier, i.e., protostellar phase. To detect signs of planet formation in the protostellar stage, the ALMA large program eDisk has been carried out in Band 6 targeting 19 protostars (16 objects are newly observed). Our sample includes 12 Class 0 and 7 Class I protostars. These protostellar disks show differences from protoplanetary disks (e.g., much fewer visible substructures and more asymmetric brightness distributions along the disk minor axis). I will present the initial results mainly about a target, Class 0 protostar IRAS 16253-2429. Previous works suggested a central mass in this protostellar system close to the brown dwarf (BD) mass limit (0.08 Msun) with a large uncertainty (M*~0.02-0.12 Msun). Precise mass measurement is crucial to identify such a protostar that will help to approach the low mass end of star formation. The 1.3 mm continuum emission at an angular resolution of 0.08" (~11 au) shows a disk-like structure with a radius of ~20 au and a possible substructure. The C18O and 13CO J=2-1 lines trace the infalling envelope, previously reported. While the 12CO J=2-1 line traces the outflow perpendicular to the dusty disk, a high-velocity component (|V-Vsys|>2 km/s) of this line suggests the presence of a Keplerian disk. The SO J_N=6_5-5_4 line shows different velocity structures, implying the presence of a ring around the Keplerian disk and a streamer from the east. Our result may provide a typical picture of protostars at the low mass end.