Constraining cosmic ray acceleration in young star clusters using multi-wavelength observations

Abstract

We use 1D and 3D two-fluid cosmic ray (CR) hydrodynamic simulations to investigate the role of CRs in the vicinity of a compact young star cluster. We model a selfgravitating cloud (density profile ρ ∝ r −1 ), include important thermal and non-thermal processes, and explore two different CR injection scenarios. We show that if internal shocks in the wind-driving region are the main site for CR acceleration, then the resulting γ-ray luminosity (L γ ) can reach ≈ 5% of the mechanical luminosity (L w ), independent of the fraction of wind energy (∼ 1 − 20%) injected into CRs. In contrast, if the forward/reverse shock of a bubble is the injection site then L γ increases linearly with the CR injection fraction, as expected analytically. We find that the X-ray luminosity (L x ) in the forward/reverse shock injection scenario is 10 −3 L w , which is ∼ 10 times larger than in the central wind-driving injection case. We predict the corresponding range of the synchrotron radio luminosity. We show how multi-wavelength observations can constrain the CR parameters. Comparing the predicted multi-wavelength luminosities with those of 30 Doradus we identify the reverse shock as the most probable CR injection site, and that thermal conduction is important. We do not find significant dynamical impact of CRs in our models.

Synthetic 26Al emission from galactic-scale superbubble simulations

“…There have been many simulations focusing on the influence of stellar feedback in galaxies. In recent years, these simulations have ranged from simulations focusing on individual superbubbles (Krause et al 2013;Gupta et al 2018;Gentry et al 2019) to 3D vertically stratified box simulations including stellar feedback in the form of supernovae (de Avillez & Breitschwerdt 2004, 2005Girichidis et al 2016). Sarkar et al (2015) present 2D simulations similar to those presented in this paper focusing on galactic outflows.…”

Role of cosmic rays in the early stages of galactic outflows

“…2) since shocks are the acceleration sites for CRs. The following conditions (Gupta et al 2018b) have been used to detect whether a particular region within the simulation box is shocked or not…”

Non-resonant Streaming Instability driven by Leptons

“…Kinetic studies of the NRSI have included the effects of the background plasma temperature [e.g., [12][13][14] and the shape of the CR distribution function [e.g., 15], always considering a current of energetic protons. Although protons are more abundant than electrons in CRs, there are environments where leptonic currents can be expected; they include: 1) quasi-perpendicular shocks, where reflected electrons can support a current in the shock upstream [16,17], which may apply, e.g., to the termination shocks from the winds of stellar clusters [18]; 2) around pulsar wind nebulae (PWNe), where both electrons and positrons are accelerated [e.g., 19, 20, references therein]; 3) the electron strahl population in the solar wind [e.g., 21].…”