Cosmic-Ray Spectra and Metal Budget Regulated by the Galactic Wind

TL;DR

This study models the impact of Galactic wind on cosmic ray spectra, reproducing observed spectral features and discussing implications for Galactic metal distribution and gamma-ray emissions.

Contribution

It introduces a velocity profile for Galactic wind that explains cosmic ray spectral features without requiring a break in diffusion coefficients.

Findings

Reproduces spectral hardening and softening in cosmic rays.

Finds a hard cosmic ray spectrum below TV at high altitudes.

Suggests wind influences metal distribution and gamma-ray emissions.

Abstract

We study the advection effect of the Galactic wind on the local cosmic ray spectra. The spectral hardening from a few hundred GV and softening from a few TV are reproduced by a velocity profile with a maximum velocity of $\sim 700~\mbox{km}~ \mbox{s}^{-1}$ without introducing a break in the power-law dependence of the diffusion coefficient. Additionally, we find that a hard CR spectrum below $\sim$ TV with an index of $\sim 2$ at an altitude $\sim 3$-$5$ kpc from the Galactic disk. This hard spectrum is favorable for the gamma-ray spectrum of the Fermi bubbles. With the obtained CR fluxes, we discuss the matter circulation in our Galaxy with the wind. While the wind has an essential role in maintaining the metal abundance in the disk, the production rate of Beryllium, which originates from CR spallation, is so low that the ratio Be/O in the halo should be larger than that in the disk gas.