ALMA view on the nature of the compact VLA continuum sources in the massive young stellar object G25.65+1.05

TL;DR

This study uses high-resolution ALMA observations to analyze the compact continuum sources in the massive young stellar object G25.65+1.05, revealing their nature, kinematics, and connection to water maser flares.

Contribution

It provides a detailed characterization of the compact sources and their association with outflows, shocks, and maser activity in G25.65+1.05, which was not previously understood.

Findings

MM1 is a hot molecular core with complex molecular spectra.

VLA 1A is a shock interface linked to water maser super flares.

Outflow and turbulence are key to maser activity.

Abstract

This paper presents high-resolution ALMA observations of the massive young stellar object G25.65+1.05, which is known to host water maser super flares. To investigate the nature of compact continuum sources that have been previously identified in this region, we analyzed 1.3 mm dust continuum and molecular line emission. The central millimeter peak MM1 coincides with the centimeter source VLA 2, has a complex molecular spectrum, and is identified as a hot molecular core. Molecular emission of SiO and CH3CN in the vicinity of MM1 reveals kinematics consistent with wide-angle outflow structures and a possible rotating disk in the source. VLA sources 1A, 1B, and 3 are lacking compact millimeter counterparts and trace shocked regions where the outflow interacts with the surrounding material. In particular, VLA 1A, the site of H2O maser super flares, is interpreted as a shock interface that exhibits developed turbulent movements seen in the SiO molecular line. The observed turbulence creates conditions required for H2O maser action, directly linking the nature of VLA 1A to the origin of the H2O maser super flares.