Non-Thermal Radiation from the Inner Galaxy

TL;DR

This paper reviews the current understanding of non-thermal radiation from the Galactic Center and Inner Galaxy, discussing potential dark matter signals, energetic astrophysical phenomena, and recent discoveries like the Fermi Bubbles.

Contribution

It provides a comprehensive overview of non-thermal emissions in the Inner Galaxy, emphasizing the complexity of interpreting signals and highlighting recent findings such as the Fermi Bubbles.

Findings

Fermi Bubbles extend ~7 kpc from the Galactic nucleus.

Microwave emission coincides with the Fermi Bubbles.

Debate exists on whether the Bubbles result from black hole activity or star formation.

Abstract

I review our current state of knowledge about non-thermal radiation from the Galactic Centre (GC) and Inner Galaxy. Definitionally, the Galactic nucleus is at the bottom of the Galaxy's gravitational well, rendering it a promising region to seek the signatures of dark matter decay or annihilation. It also hosts, however, the Milky Way's resident supermassive black hole and up to 10% of current massive star formation in the Galaxy. Thus the Galactic nucleus is a dynamic and highly-energized environment implying that extreme caution must be exercised in interpreting any unusual or unexpected signal from (or emerging from) the region as evidence for dark matter-related processes. One spectacular example of an `unexpected' signal is the discovery within the last few years of the `Fermi Bubbles' and, subsequently, their polarised radio counterparts. These giant lobes extend ~7 kpc from the nucleus into both north and south Galactic hemispheres. Hard-spectrum, microwave emission coincident with the lower reaches of the Bubbles has also been detected, first in WMAP, and more recently in Planck data. Debate continues as to the origin of the Bubbles and their multi-wavelength emissions: are they the signatures of relatively recent (in the last ~Myr) activity of the supermassive black hole or, alternatively, nuclear star formation? I will briefly review evidence that points to the latter interpretation.