Origin of the Cosmic Ray Galactic Halo Driven by Advected Turbulence and Self-Generated Waves

TL;DR

This paper proposes a physical model where cosmic ray diffusion and halo formation result from wave self-generation and advection, naturally explaining observed halo sizes and spectral features without relying solely on fitted parameters.

Contribution

It introduces a novel scenario deriving cosmic ray diffusion properties from wave self-generation and advection, leading to a naturally formed halo consistent with observations.

Findings

A galactic halo of a few kiloparsecs naturally emerges from the model.

Transport in the halo causes a spectral hardening of primary cosmic rays around 300 GV.

The model aligns with observed halo sizes and cosmic ray spectral features.

Abstract

The diffusive paradigm for the transport of Galactic cosmic rays is central to our understanding of the origin of these high energy particles. However, it is worth recalling that the normalization, energy dependence, and spatial extent of the diffusion coefficient in the interstellar medium are fitted to the data and typically are not derived from more basic principles. Here, we discuss a scenario in which the diffusion properties of cosmic rays are derived from a combination of wave self-generation and advection from the Galactic disc, where the sources of cosmic rays are assumed to be located. We show for the first time that a halo naturally arises from these phenomena, with a size of a few kiloparsecs, compatible with the value that typically best fits observations in simple parametric approaches to cosmic ray diffusion. We also show that transport in such a halo results in a hardening in the spectra of primary cosmic rays at ~300 GV.