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

Feedback from outflows driven by active galactic nuclei (AGN) can affect the distribution and properties of the gaseous haloes 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 disc baryonic concentration of the galaxy. We show that the outflow velocity levels off at ∼ 10³ km s^{- 1} within the scale of the galaxy disc. Typically, the outflow can reach the virial radius around the time when the AGN shuts off. We show that the outflows are energy-driven, consistent with observations and recent theoretical findings. The outflow shock lights up the haloes of massive galaxies across a broad wavelength range. For Milky Way mass haloes, radio observations by the Jansky Very Large Array and the Square Kilometre Array and infrared/optical observations by the James Webb Space Telescope and Hubble Space Telescope can detect the emission signal of angular size ∼8 arcsec from galaxies out to redshift z ∼ 5. Millimetre observations by the Atacama Large Millimeter/submillimeter Array are sensitive to non-thermal emission of angular size ∼18 arcsec from galaxies at redshift z ≲ 1, while X-ray observations by Chandra, XMM-Newton and the Advanced Telescope for High Energy Astrophysics are limited to local galaxies (z ≲ 0.1) with an emission angular size of ∼2 arcmin. Overall, the extended non-thermal emission provides a new way of probing the gaseous haloes of galaxies at high redshifts.