Probing the Star-forming Mechanism in G25.82-0.17: Water Maser Parallax and CO Outflow Properties

ABSTRACT :
We present a comprehensive investigation of the molecular environment surrounding G25.82-W1, a high-mass young stellar object (HM-YSO), utilizing water maser observations at 22 GHz and the CO 2–1line data. From the VLBI Exploration of Radio Astrometry (VERA) monitoring observations, we determined the parallax of water masers to be 0.225 mas. A trigonometric distance of 4.50 kpc is estimated, crucial for calculating the physical properties of YSOs. Korean VLBI Network and VERA arrays (KaVA) monitoring observations provided insights into the internal proper motions of water masers, revealing a mixture of random motion and expansion centered around G25.82-W1. In addition, an extended and wide opening-angle N–S CO outflow is revealed by Atacama Large Millimeter/submillimeter Array (ALMA) driven from G25.82-W1, with a compact structure moving at high velocities along the line of sight near the source. Water masers are likely trace the expanding shell portion of the N–S CO outflow originating overlapped region near the driving point. The outflow force of the N–S CO outflow is calculated as 1.66 x 10−4 M km /s /yr, aligning with expectations based on its luminosity and suggesting a common mechanism for outflow generation across star-forming regions of varying mass. These findings support that the star-forming mode in G25.82 represents a scaled-up version of low-mass star formation.