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arXiv · 2611.08891

Predicting Continuum Emission in Massive Star-Forming Regions with Embedded HII Regions - Dust, Free-Free, and Anomalous Microwave Emission with POLARIS

Stefan Reissl·Alessio Traficante·Paolo Suin·Alice Nucara·Ralf S. Klessen·Leonardo Testi
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Abstract

Context: HII regions are a key stage of massive star formation, where ionizing radiation reshapes the interstellar medium. Their continuum spectra trace thermal dust, free-free emission, and anomalous microwave emission (AME). Aims: We investigate how these components evolve as an HII region expands and correlate with gas and electron column densities across spatial scales. Methods: We post-process RAMSES radiation-magnetohydrodynamical simulations of a $10^4 M_\odot$ cloud with POLARIS. The model includes grain charging, rotational excitation and damping, radiative torques, rotational disruption, and emission from dust, ionized gas, and nano-composite grains. We compute maps and SEDs for six snapshots over $1-10^4$ GHz and analyze multi-scale correlations. Results: Ionized emission evolves from a compact, optically thick HII region to an extended, optically thin structure. Around 15 GHz, free-free emission changes from a $ν^2$ to a $ν^{-0.1}$ spectral regime as optical depth decreases, and increasingly traces electron column density. The thermal dust peak shifts from mid- to far-infrared as colder material contributes, while dust emission remains strongly correlated with total gas column density. AME peaks at 26-37 GHz and shows scale-dependent correlations with gas and electron distributions. Rotational disruption is the main dust-destruction mechanism affecting mid-infrared emission and the high-frequency AME tail. Conclusions: These continuum components provide complementary, scale-dependent diagnostics of stellar feedback. Self-consistent multi-frequency modeling is essential for interpreting surveys of star-forming clouds.

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Stefan Reissl, Alessio Traficante, Paolo Suin, Alice Nucara, Ralf S. Klessen, Leonardo Testi. 2026-11-06. Predicting Continuum Emission in Massive Star-Forming Regions with Embedded HII Regions - Dust, Free-Free, and Anomalous Microwave Emission with POLARIS. https://arxiv.org/abs/2611.08891

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