We present results of continuum and spectral line observations with ALMA and 22 GHz water ( H _ { 2 } O ) maser observations using KaVA and VERA 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 ultra-compact 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 CH _ { 3 } OH 8 _ { -1 } –7 _ { 0 } E line , known to be a class I CH _ { 3 } OH maser at 229 GHz is also detected showing a mixture of thermal and maser emission .
Moreover , the H _ { 2 } O masers are distributed in a region \sim 0.25 \arcsec shifted from G25.82–W1 .
The CH _ { 3 } OH 22 _ { 4 } –21 _ { 5 } E line shows a compact ring-like 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 _ { \odot } and the total mass of 20 M _ { \odot } -84 M _ { \odot } 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 .