2020ApJ...896..127K

We present results of continuum and spectral line observations with Atacama Large Millimeter/submillimeter Array (ALMA) and 22 GHz water (H₂O) maser observations using the KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry) array (KaVA) toward a high-mass star-forming region, G25.82-0.17. Multiple 1.3 mm continuum sources are revealed, indicating the presence of young stellar objects (YSOs) at different evolutionary stages, namely an ultracompact H II region, G25.82-E, a high-mass young stellar object (HM-YSO), G25.82-W1, and starless cores, G25.82-W2 and G25.82-W3. Two SiO outflows, at N-S and SE-NW orientations, are identified. The CH₃OH 8_–1-7₀ E line, known to be a Class I CH₃OH maser at 229 GHz, is also detected, showing a mixture of thermal and maser emission. Moreover, the H₂O masers are distributed in a region ∼0.''25 shifted from G25.82-W1. The CH₃OH 22₄-21₅ E line shows a compact ringlike structure at the position of G25.82-W1 with a velocity gradient, indicating a rotating disk or envelope. Assuming Keplerian rotation, the dynamical mass of G25.82-W1 is estimated to be >25 M_☉ and the total mass of 20-84 M_☉ is derived from the 1.3 mm continuum emission. The driving source of the N-S SiO outflow is G25.82-W1 while that of the SE-NW SiO outflow is uncertain. Detection of multiple high-mass starless/protostellar cores and candidates without low-mass cores implies that HM-YSOs could form in individual high-mass cores as predicted by the turbulent core accretion model. If this is the case, the high-mass star formation process in G25.82 would be consistent with a scaled-up version of low-mass star formation.