An Extensive, Sensitive Search for SiO Masers in High- and Intermediate-Mass Star-Forming Regions

TL;DR

This study used sensitive VLA observations to search for SiO masers in 60 star-forming regions, confirming their rarity and associating them with extreme physical conditions, while also providing continuum emission images.

Contribution

It is the first extensive survey of SiO masers in high- and intermediate-mass star-forming regions, confirming their scarcity and linking them to specific physical conditions.

Findings

SiO masers detected in only three luminous regions: Orion-KL, W51N, Sgr B2(M).

SiO maser emission is a rare phenomenon requiring extreme conditions.

Continuum images suggest free-free emission from compact HII regions.

Abstract

We present sensitive Very Large Array observations with an angular resolution of a few arcseconds of the $J= 1 - 0$ line of SiO in the $v$=1 and 2 vibrationally excited states toward a sample of 60 Galactic regions in which stars of high or intermediate mass are currently forming and/or have recently formed. We report the detection of SiO maser emission in \textit{both} vibrationally excited transitions toward only three very luminous regions: Orion-KL, W51N and Sgr B2(M). Toward all three, SiO maser emission had previously been reported, in Orion-KL in both lines, in W51N only in the $v=2$ line and in Sgr B2(M) only in the $v=1$ line. Our work confirms that SiO maser emission in star-forming regions is a rare phenomenon, indeed, that requires special, probably extreme, physical and chemical conditions not commonly found. In addition to this SiO maser survey, we also present images of the simultaneously observed 7 mm continuum emission from a subset of our sample of star-forming regions where such emission was detected. This is in most cases likely to be free-free emission from compact- and ultracompact-HII regions.