Wild at Heart:-The Particle Astrophysics of the Galactic Centre

TL;DR

This paper models the high-energy astrophysics of the Galactic Centre, showing how supernovae drive cosmic ray populations, winds, and large-scale emissions, and constraining magnetic fields and cosmic ray penetration.

Contribution

It provides a comprehensive model linking supernova activity to various non-thermal emissions and cosmic ray phenomena in the Galactic Centre, with new bounds on magnetic fields and cosmic ray behavior.

Findings

Supernovae sustain cosmic ray populations and drive winds in the Galactic Centre.

Magnetic field strength in the region is constrained between 60 and 400 microGauss.

TeV cosmic rays likely do not penetrate dense molecular clouds before being advected away.

Abstract

We treat of the high-energy astrophysics of the inner ~200 pc of the Galaxy. Our modelling of this region shows that the supernovae exploding here every few thousand years inject enough power to i) sustain the steady-state, in situ population of cosmic rays (CRs) required to generate the region's non-thermal radio and TeV {\gamma}-ray emis-sion; ii) drive a powerful wind that advects non-thermal particles out of the inner GC; iii) supply the low-energy CRs whose Coulombic collisions sustain the temperature and ionization rate of the anomalously warm, envelope H2 detected throughout the Cen-tral Molecular Zone; iv) accelerate the primary electrons which provide the extended, non-thermal radio emission seen over ~150 pc scales above and below the plane (the Galactic centre lobe); and v) accelerate the primary protons and heavier ions which, advected to very large scales (up to ~10 kpc), generate the recently-identified WMAP haze and corresponding Fermi haze/bubbles. Our modelling bounds the average magnetic field amplitude in the inner few degrees of the Galaxy to the range 60 < B/microG < 400 (at 2 sigma confidence) and shows that even TeV CRs likely do not have time to penetrate into the cores of the region's dense molecular clouds before the wind removes them from the region. This latter finding apparently disfavours scenarios in which CRs - in this star-burst-like environment - act to substantially modify the conditions of star-formation. We speculate that the wind we identify plays a crucial role in advecting low-energy positrons from the Galactic nucleus into the bulge, thereby explaining the extended morphology of the 511 keV line emission. (abridged)