Spinning Nanoparticles Impacted by C-shock: Implications for Radio-millimeter Emission from Star-forming Regions

TL;DR

This paper explores how C-shocks in star-forming regions can suppress anomalous microwave emission from spinning nanoparticles, affecting the radio-millimeter spectral energy distribution.

Contribution

It introduces a model linking C-shock impacts to AME suppression, providing insights into the evolution of emission in star-forming regions.

Findings

C-shocks can significantly suppress AME in certain ISM conditions.

The suppression depends on grain tensile strength and shock parameters.

This mechanism explains the rarity of observed AME in extragalactic star-forming regions.

Abstract

We investigate the impact of anomalous microwave emission (AME) on the radio-millimeter spectral energy distribution for three typical interstellar medium (ISM) conditions surrounding star-forming regions -- cold neutral medium, warm neutral medium, and photodissociation region -- by comparing the emissivities of three major contributors: free-free, thermal dust emission, and AME. In particular, for spinning nanoparticles (i.e., potential carriers of AME), we consider a known grain destruction mechanism due to a centrifugal force from spin-up processes caused by collisions between dust grains and supersonic neutral streams in a magnetized shock (C-shock). We demonstrate that, if the ISM in a magnetic field is impacted by a C-shock developed by a supernova explosion in the early phase of massive star-formation ($\lesssim 10$ Myr), AME can be significantly or almost entirely suppressed relative to free-free and thermal dust continuum emission if the grain tensile strength is small enough. This study may shed light on explaining the rare observations of AME from extragalactic star-forming regions preferentially observed from massive star clusters and suggest a scenario of "the rise and fall of AME" in accordance with the temporal evolution of star-forming regions.