ALMA observations of submillimeter H2O and SiO lines in Orion Source I

TL;DR

This study uses ALMA to observe submillimeter H2O and SiO lines in Orion Source I, revealing compact disk structures, outflow dynamics, and maser activity, advancing understanding of high-mass star formation processes.

Contribution

First detailed ALMA observations of high-excitation H2O and SiO lines in Orion Source I, highlighting disk rotation, outflow features, and maser emission at submillimeter wavelengths.

Findings

Compact structures consistent with circumstellar disk and outflow base.

Velocity gradients indicating disk rotation.

Detection of strong H2O maser emission.

Abstract

We present observational results of the submillimeter H2O and SiO lines toward a candidate high-mass young stellar object Orion Source I using ALMA. The spatial structures of the high excitation lines at lower-state energies of >2500 K show compact structures consistent with the circumstellar disk and/or base of the northeast-southwest bipolar outflow with a 100 au scale. The highest excitation transition, the SiO (v=4) line at band 8, has the most compact structure. In contrast, lower-excitation transitions are more extended than 200 au tracing the outflow. Almost all the line show velocity gradients perpendicular to the outflow axis suggesting rotation motions of the circumstellar disk and outflow. While some of the detected lines show broad line profiles and spatially extended emission components indicative of thermal excitation, the strong H2O lines at 321 GHz, 474 GHz, and 658 GHz with brightness temperatures of >1000 K show clear signatures of maser action.