Subarcsecond Imaging of the High-Mass Star Forming Region Onsala 1

TL;DR

This study presents high-resolution subarcsecond imaging of the high-mass star forming region Onsala 1, revealing multiple sources and signs of ongoing star formation, indicating a complex, evolving environment with potential for future star formation activity.

Contribution

First subarcsecond imaging of ON 1 with SMA and VLA, identifying multiple sources and early-stage star formation cores within a compact region.

Findings

Discovered two new cm-wave sources and five sub-mm dust sources.

Identified a likely intermediate-mass star forming core, SMA2.

Estimated star formation efficiency of about 10%, suggesting ongoing star formation.

Abstract

We report subarcsecond images of the high-mass star forming region Onsala 1 (ON 1) made with the Submillimeter Array (SMA) at 0.85 mm and the Very Large Array at 1.3 cm and 3.6 cm. ON~1 is one of the smallest ultracompact HII regions in the Galaxy and exhibits various star formation signposts. With our VLA and SMA observations, two new cm-wave sources and five sub-mm dust sources, respectively, within a field of ~3" (corresponding to a linear scale of 0.05 pc) are identified, indicating the multiplicity at the center of the ON 1 region. The dust and gas masses of these sub-mm sources are in the range of 0.8 to 6.4 M_sun. Among the five sub-mm dust sources, SMA2, with a dust and gas mass of 2.6 M_sun, demonstrates several star formation signatures, and hence likely represents an intermediate-mass (or even high-mass) star forming core. Due to the low star formation efficiency of ~10%, we suggest that star formation in the ON 1 region will continue. For example, SMA4 and SMA5 are not associated with any star formation signatures and likely mark star formation cores at very early evolutionary stages.