Spectroscopic Observations of the Fermi Bubbles

TL;DR

This paper reviews spectroscopic studies of the Fermi Bubbles, giant plasma structures above and below the Galactic Center, discussing their properties, origins, and the future research needed to understand their impact on the Galaxy.

Contribution

It synthesizes current spectroscopic findings on the Fermi Bubbles and outlines key open questions and future observational strategies for studying nuclear winds in our Galaxy.

Findings

Spectroscopic data reveal the kinematics and chemical composition of outflowing gas.

The origin of the Bubbles remains debated between AGN activity and star formation.

Further UV and radio spectroscopy are needed to understand the physical conditions.

Abstract

Two giant plasma lobes, known as the Fermi Bubbles, extend 10 kpc above and below the Galactic Center. Since their discovery in X-rays in 2003 (and in gamma-rays in 2010), the Bubbles have been recognized as a new morphological feature of our Galaxy and a striking example of energetic feedback from the nuclear region. They remain the subject of intense research and their origin via AGN activity or nuclear star formation is still debated. While imaging at gamma-ray, X-ray, microwave, and radio wavelengths has revealed their morphology and energetics, spectroscopy at radio and UV wavelengths has recently been used to study the kinematics and chemical abundances of outflowing gas clouds embedded in the Bubbles (the nuclear wind). Here we identify the scientific themes that have emerged from the spectroscopic studies, determine key open questions, and describe further observations needed in the next ten years to characterize the basic physical conditions in the nuclear wind and its impact on the rest of the Galaxy. Nuclear winds are ubiquitous in galaxies, and the Galactic Center represents the best opportunity to study the constitution and structure of a nuclear wind in close detail.