Probing the gaseous halo of galaxies through non-thermal emission from AGN-driven outflows

Abstract

Feedback from outflows driven by active galactic nuclei (AGN) can affect the distribution and properties of the gaseous halos of galaxies. We study the hydrodynamics and non-thermal emission from the forward outflow shock produced by an AGN-driven outflow. We consider a few possible profiles for the halo gas density, self-consistently constrained by the halo mass, redshift and the disk baryonic concentration of the galaxy. We show that the outflow velocity levels off at $\sim 10^3\,\rm km\, s^{-1}$ within the scale of the galaxy disk. Typically, the outflow can reach the virial radius around the time when the AGN shuts off. We show that the outflows are energy-driven, consistently with observations and recent theoretical findings. The outflow shock lights up the halos of massive galaxies across a broad wavelength range. For Milky Way (MW) mass halos, radio observations by The Jansky Very Large Array (JVLA) and The Square Kilometer Array (SKA) and infrared/optical observations by The James Webb Space Telescope (JWST) and Hubble Space Telescope (HST) can detect the emission signal of angular size $\sim 8"$ from galaxies out to redshift $z\sim5$. Millimeter observations by The Atacama Large Millimeter/submillimeter Array (ALMA) are sensitive to non-thermal emission of angular size $\sim 18"$ from galaxies at redshift $z\lesssim1$, while X-ray observations by Chandra, XMM-Newton and The Advanced Telescope for High Energy Astrophysics (ATHENA) is limited to local galaxies ($z\lesssim 0.1$) with an emission angular size of $\sim2'$. Overall, the extended non-thermal emission provides a new way of probing the gaseous halos of galaxies at high redshifts.