7 mm continuum observations of ultra compact HII regions

TL;DR

This study evaluates the potential of the ESA Planck mission to detect ultra compact HII regions by performing 7 mm observations, modeling their spectra, and estimating their detectability based on flux densities and instrument sensitivity.

Contribution

It provides the first assessment of Planck's capability to detect UCHII regions, highlighting detection probabilities based on source location in the Galaxy.

Findings

Planck will have a low detection rate for sources near the Galactic center.

High detection probability if sources are located near the Galactic anticenter.

Spectral modeling helps estimate flux densities across radio to sub-millimeter bands.

Abstract

Ultra compact HII (UCHII) regions are indicators of high-mass star formation sites and are distributed mainly in the Galactic plane. We intend to investigate the possible contribution of the forthcoming ESA Planck mission to the science of UCHII regions by evaluating the possibility of detecting UCHIIs that are bright in the radio regime. We performed new 7 mm observations of a sample of UCHII regions. For each source in our sample, the free-free radio spectrum has been modeled. Along with far-IR measurements, our spectra allow us to estimate the flux densities of the sources in the millimeter and sub-millimeter bands. The possibility of Planck detecting the selected sources can be assessed by comparing the estimated flux densities to the expected sensitivity in each Planck channel. We conclude that, in the case of the present sample, located close to the Galactic center, Planck will have a very low detection rate. In contrast, assuming that our sample is representative of the whole UCHII-region population, we derive a very high probability of detecting this kind of source with Planck if located instead close to the anticenter.