Detection of 25 GHz CH₃OH Emission in Broadband Continuum Observations of Ionized Jet Candidates

In recent years high-sensitivity radio continuum surveys of young high-mass star forming regions have resulted in the detection of many ionized jets and ionized jet candidates. Among them, the survey of Rosero et al. (2016, 2019) identified 70 weak radio continuum sources, ~30% of which were consistent with ionized jets (including candidates). The observations of Rosero et al. (2016) were conducted with the VLA’s WIDAR correlator, in which every continuum spectral window is effectively a low-resolution spectral line scan. We searched for CH₃OH emission from the 25 GHz ladder in the continuum dataset of Rosero et al. (2016), and detected 10 sources with CH₃OH lines. The transitions are from the 6(2)-6(1) to the 10(2)-10(1) lines; most sources were detected in the 6(2)-6(1) to 9(2)-9(1) transitions. Given the large channel width of the observations (~24 km/s), it is not possible to disentangle in most cases the nature of the lines, i.e., thermal emission vs masers. However, it is likely that the sample contains a mixture of both thermal and non-thermal lines. Out of the 10 sources, at least seven have been classified as ionized jets or jet candidates, which suggests a prevalence of excited CH₃OH emission from the 25 GHz ladder in ionized jet sources. Most of the CH₃OH lines were detected near the radio continuum peak, therefore excited CH₃OH lines could be useful to investigate the connection between ionized jets and the molecular environment, i.e., the regions where ionized jets could drive the development of molecular outflows. This work is partially supported by NSF grants AST-1814063 and AST-1814011, and computational resources donated by WIU Distinguished Alumnus Frank Rodeffer.