Irradiated shocks in the W28 A2 massive star-forming region: a site for cosmic rays acceleration?

TL;DR

This paper investigates whether irradiated shocks in the W28 A2 massive star-forming region can accelerate cosmic rays, using multi-telescope observations to analyze the physical conditions conducive to such acceleration.

Contribution

It presents a detailed observational study of irradiated shocks in W28 A2, exploring their potential role in in situ cosmic ray acceleration, which is a novel focus in this context.

Findings

Presence of strong magnetic fields and high ionization in shocks.

Evidence of energetic processes capable of accelerating cosmic rays.

Insights into the interaction between massive star formation and cosmic ray production.

Abstract

The formation of massive stars play a crucial role in galaxies from numerous points of view. The protostar generates a strong ultraviolet radiation field that ionizes its surroundings, and it drives powerful shock waves in the neighbouring medium in the form of jets and bipolar outflows, whose structure can be partially organized by local, strong magnetic field. Such an ejection activity locally modifies the interstellar chemistry, contributing to the cycle of matter. It also significantly participates to the energetic balance of galaxies. In the latter stages of massive star formation, the protostar is surrounded by an ultra-compact HII region, and irradiates its bipolar outflows, where an intrinsically strong magnetic field structure is associated to the generally high densities. In the HII region, or in the bipolar outflows, the question of in situ cosmic rays acceleration can then be raised by the simultaneous presence of strong magnetic fields, significant ionization of the matter, and mechanical energy available in large quantities. In this contribution, we will only summarise the results of our study of potential in situ cosmic rays acceleration the irradiated shocks in the W28 A2 massive star forming region, based on observations from the APEX, IRAM 30m, and Herschel telescopes, and presented in Gusdorf et al., recently submitted to A&A.