SCOTCH -- Search for Clandestine Optically Thick Compact HIIs

TL;DR

This paper searches for hypercompact HII regions using high-frequency radio data near methanol masers, identifying promising candidates for very young high-mass star formation stages.

Contribution

It introduces a new method combining 23 GHz continuum data with methanol maser locations to identify HC HII region candidates, expanding the search for these rare objects.

Findings

Detected 68 high-frequency radio sources in 128 fields.

Identified 49 HII regions, 47 embedded in dense clumps.

Found 13 methanol maser sites with radio sources indicating potential HC HII regions.

Abstract

This study uses archival high frequency continuum data to expand the search for Hypercompact HII regions and determine the conditions at which they appear, as this stage high mass star formation is short-lived and rare. We use 23 GHz continuum data taken towards methanol masers, which are an excellent signpost for very young embedded high-mass protostars. We have searched for high-frequency, optically thick radio sources to identify HC HII region candidates. The data cover 128 fields that include 141 methanol masers identified by the Methanol Multibeam (MMB) survey. We have detected 68 high-frequency radio sources and conducted a multi-wavelength analysis to determine their nature. This has identified 49 HII regions, 47 of which are embedded in dense clumps fourteen of which do not have a 5 GHz radio counterpart. We have identified 13 methanol maser sites that are coincident with radio sources that have a steep positive spectral index. The majority of these are not detected in the mid-infrared and have been classified as protostellar or young stellar objects in the literature and we therefore consider to be good HC HII region candidates, however, further work and higher resolution data are needed to confirm these candidates.