A Survey for Hydroxyl in the THOR Pilot Region around W43

TL;DR

This survey maps hydroxyl radicals in the W43 star-forming region, identifying numerous maser sites and diffuse emission, revealing their association with star formation and evolved stars, and providing insights into the region's molecular environment.

Contribution

First comprehensive survey of hydroxyl masers and diffuse emission in the W43 region, linking maser types to star formation and stellar evolution.

Findings

103 maser sites identified, including 72 with 1612 MHz masers.

Most main-line and 1720 MHz masers are associated with star formation.

Diffuse OH emission and absorption detected, especially towards W43 Main.

Abstract

We report on observations of the hydroxyl radical (OH) within The H{\sc I}, OH Recombination line survey (THOR) pilot region. The region is bounded approximately between Galactic coordinates l=29.2 to 31.5$^\circ$ and b=-1.0 to +1.0$^\circ$ and includes the high-mass star forming region W43. We identify 103 maser sites, including 72 with 1612\,MHz masers, 42 showing masers in either of the main line transitions at 1665 and 1667\,MHz and four showing 1720\,MHz masers. Most maser sites with either main-line or 1720\,MHz emission are associated with star formation, whereas most of the 1612\,MHz masers are associated with evolved stars. We find that nearly all of the main-line maser sites are co-spatial with an infrared source, detected by GLIMPSE. We also find diffuse OH emission, as well as OH in absorption towards selected unresolved or partially resolved sites. Extended OH absorption is found towards the well known star forming complex W43 Main.