Hadronic Interactions of Energetic Charged Particles in Protogalactic Outflow Environments and Implications for the Early Evolution of Galaxies

Abstract

We investigate the interactions of energetic hadronic particles with the media in outflows from star-forming protogalaxies. These particles undergo pion-producing interactions which can drive a heating effect in the outflow, while those advected by the outflow also transport energy beyond the galaxy, heating the circumgalactic medium. We investigate how this process evolves over the length of the outflow and calculate the corresponding heating rates in advection-dominated and diffusion-dominated cosmic ray transport regimes. In a purely diffusive transport scenario, we find the peak heating rate reaches 10 −26 erg cm −3 s −1 at the base of the outflow where the wind is driven by core-collapse supernovae at an event rate of 0.1 yr −1 , but does not extend beyond 2 kpc. In the advection limit, the peak heating rate is reduced to 10 −28 erg cm −3 s −1 , but its extent can reach to tens of kpc. Around 10% of the cosmic rays injected into the system can escape by advection with the outflow wind, while the remaining cosmic rays deliver an important interstellar heating effect. We apply our cosmic ray heating model to the recent observation of the high-redshift galaxy MACS1149-JD1 and show that it could account for the quenching of a previous starburst inferred from spectroscopic observations. Re-ignition of later star-formation may be caused by the presence of filamentary circumgalactic inflows which are reinstated after cosmic ray heating has subsided.

Observational Signatures of Cosmic-Ray Interactions in Molecular Clouds

“…CR heating has been argued to be important in the ISM of galaxies (Field et al 1969;Wiener et al 2013b;Walker 2016;Owen et al 2018Owen et al , 2019b in their circumgalactic environments (e.g., Salem et al 2016;Owen et al 2019aOwen et al , 2019b, and even in the intra-cluster medium between galaxies (e.g., Loewenstein et al 1991;Wiener et al 2013a;Ruszkowski et al 2017). Its power is mediated by the thermalization mechanism(s) at work, as governed by the local conditions (e.g., density, ionization fraction, magnetic field).…”

A hydrodynamical study of outflows in starburst galaxies with different driving mechanisms

“…co-variant polarised radiative transfer methods (Chan et al 2019). Cosmic rays may also deposit energy to heat and ionise matter at high flow altitudes (Owen et al 2019a) possibly reaching into the circumgalactic and/or intergalactic medium, and this may contribute to the progression of cosmic pre-heating and reionisation (e.g. Sazonov & Sunyaev 2015;Leite et al 2017).…”

“…These advected cosmic rays may also provide pressure support around and between galaxies to balance against gravitational collapse in low-redshift clusters (Suto et al 2013;Biffi et al 2016) or affect the separation of bright neighbouring star-forming galaxies at high-redshift (Owen et al 2019a).…”

Outflows from starburst galaxies with various driving mechanisms and their X-ray properties

“…The increase in flow velocity would be more moderate through this point if a smoother boundary to the injection region is considered, as shown in some studies (e.g. Owen et al 2019a). Provided that the total amount of material and energy injected in the flow beyond the starburst region is properly accounted for, the detailed treatment of the micro-physics in the transitional boundary interface zone has inconsequential global impacts on the macroscopic HD structures and thermal properties of a galactic outflow.…”