Ultracompact H ii regions with extended emission: the case of G43.89–0.78 and its molecular environment

Abstract

ABSTRACT The Karl Jansky Very Large Array (VLA), Owens Valley Radio Observatory (OVRO), Atacama Large Millimetric Array (ALMA), and the infrared Spitzer observatories are powerful facilities to study massive star formation regions and related objects such as ultra-compact (UC) H ii regions, molecular clumps, and cores. We used these telescopes to study the UC H ii region G43.89–0.78. The morphological study at arcminute scales using NVSS and Spitzer data shows that this region is similar to those observed in the bubble-like structures revealed by 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 UC H ii region 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 UC H ii region. Using ALMA observations, we detect the presence of a dense (2.6 × 107 cm−3) and small (∼ 2.0 arcsec; 0.08 pc) molecular clump with a mass of 220 M⊙ and average kinetic temperature of 21 K, located near to the UC H ii 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 (Td = 50 K; M = 11 M⊙) and G43.888–0.787 (Td = 50 K; M = 15 M⊙).