The Coordinated Radio and Infrared Survey for High-Mass Star Formation III. A catalogue of northern ultra-compact H II regions

TL;DR

This paper presents a comprehensive catalogue of 239 ultra-compact HII regions from the CORNISH survey, analyzing their properties and variability to enhance understanding of massive star formation.

Contribution

It provides the largest complete sample of UCHIIs with detailed multi-wavelength data and physical properties, improving the understanding of their role in star formation.

Findings

Identified ~750 UCHIIs in the Galaxy, fewer than previous surveys.

Detected about 5% of sources show time variability.

Reconstructed spectral energy distributions for 177 UCHIIs.

Abstract

A catalogue of 239 ultra-compact HII regions (UCHIIs) found in the CORNISH survey at 5 GHz and 1.5" resolution in the region $10^{\circ} < l < 65^{\circ}, ~|b| < 1^{\circ}$ is presented. This is the largest complete and well-selected sample of UCHIIs to date and provides the opportunity to explore the global and individual properties of this key state in massive star formation at multiple wavelengths. The nature of the candidates was validated, based on observational properties and calculated spectral indices, and the analysis is presented in this work. The physical sizes, luminosities and other physical properties were computed by utilising literature distances or calculating the distances whenever a value was not available. The near- and mid-infrared extended source fluxes were measured and the extinctions towards the UCHIIs were computed. The new results were combined with available data at longer wavelengths and the spectral energy distributions (SEDs) were reconstructed for 177 UCHIIs. The bolometric luminosities obtained from SED fitting are presented. By comparing the radio flux densities to previous observational epochs, we find about 5% of the sources appear to be time variable. This first high-resolution area survey of the Galactic plane shows that the total number of UCHIIs in the Galaxy is ~ 750 - a factor of 3-4 fewer than found in previous large area radio surveys. It will form the basis for future tests of models of massive star formation.