Ultracompact HII regions with extended emission: The case of G43.89-0.78 and its molecular environment

The Karl Jansky Very Large Array (VLA), Owens Valley Radio Observatory (OVRO), Atacama Large Millimetric Array (ALMA), and the infrared $\mathit{\text{Spitzer}}$ observatories, are powerful facilities to study massive star formation regions and related objects such as ultra–compact (UC) \hii regions, molecular clumps, and cores. We used these telescopes to study the \uchiir G43.89–0.78. The morphological study at arcminute scales using NVSS and $\mathit{\text{Spitzer}}$ data shows that this region is similar to those observed in the $\mathit{\text{bubble–like}}$ structures revealed by $\mathit{\text{Spitzer}}$ observations. With this result, and including a physical characterization based on 3.6 cm data, we suggest G43.89–0.78 be classified as an \uchiir with Extended Emission because it meets the operational definition given in this paper comparing radio continuum data at 3.6 and 20~cm. For the ultra-compact component, we use VLA data to obtain physical parameters at 3.6~cm confirming this region as an \uchii region. Using ALMA observations, we detect the presence of a dense ($2.6\times {10}^7$ cm${}^{-3}$) and small ($\sim$ 2.0\arcsec; 0.08 pc) molecular clump with a mass of 220 M${}_{\odot }$ and average kinetic temperature of 21~K, located near to the \uchii region. In this clump, catalogued as G43.890–0.784, water masers also exist, possibly tracing a bipolar outflow. We discover in this vicinity two additional clumps which we label as G43.899–0.786 (T${}_d$ = 50 K; M = 11 M${}_{\odot }$), and G43.888–0.787 (T${}_d$ = 50 K; M = 15 M${}_{\odot }$).