CANDIDATES FOR THE YOUNG STELLAR OUTFLOWS: WATER AND METHANOL MASERS FROM YOUNG STELLAR OBJECTS

We conducted simultaneous 22 GHz water maser and 44 GHz class I methanol maser surveys of newly identified 282 H 2 emission features from the 2.122 μm H 2 narrowband image survey in the Galactic plane (UWISH2 project) using Korean VLBI Network 21 m radio telescopes. We detected 16 and 13 new water and methanol maser sources, respectively. This result indicates that at least ∼5% of the H 2 emission features originate from young stellar objects (YSOs) that are in the right physical condition to produce the water and methanol masers. The masers are closely related to the current outflow activities in the Galactic plane. The power sources of these 23 diffused/collimated H 2 emission features (six sources are detected for both masers) are likely to be intermediate- to high-mass YSOs, based on a comparison with the maser luminosities of other well-studied YSOs. Both maser velocities are mostly close to their own systemic velocities within ≲5 km s −1 , even though water masers generally show larger variabilities in the intensity, velocity, and shape than methanol masers. We also discovered three new water maser sources with high-velocity components: ∼25 km s −1 redshifted CMHO 019, ∼50 km s −1 blueshifted CMHO 132, and ∼120 km s −1 blueshifted CMHO 182. In particular, we propose that the dominant blueshifted water maser of CHMO 182 can be a unique laboratory for the study of the high-mass young stellar jet and its acceleration.