A Survey for Hydroxyl in the THOR Pilot Region around W43

We report on observations of the hydroxyl radical (OH) within The HI, OH Recombination line survey (THOR) pilot region. The region is bounded approximately between Galactic coordinates l=29.2 to 31.5◦ and b=-1.0 to +1.0◦ and includes the high-mass star forming region W43. We identify 103 maser sites, including 72 with 1612MHz masers, 42 showing masers in either of the main line transitions at 1665 and 1667MHz and four showing 1720MHz masers. Most maser sites with either mainline or 1720MHz emission are associated with star formation, whereas most of the 1612MHz 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.