Radio mode feedback: Does relativity matter?

Abstract

Radio mode feedback, associated with the propagation of powerful outflows in active galaxies, is a crucial ingredient in galaxy evolution. Extragalactic jets are well collimated and relativistic, both in terms of thermodynamics and kinematics. They generate strong shocks in the ambient medium, associated with observed hotspots, and carve cavities that are filled with the shocked jet flow. In this Letter, we compare the pressure evolution in the hotspot and the cavity generated by relativistic and classical jets. Our results show that the classical approach underestimates the cavity pressure by a factor ≥ 2 for a given shocked volume during the whole active phase. The tension between both approaches can only be alleviated by unrealistic jet flow densities or gigantic jet areas in the classical case. As a consequence, the efficiency of a relativistic jet heating the ambient is typically ∼ 20% larger compared with a classical jet, and the heated volume is 2 to 10 times larger during the time evolution. This conflict translates into two substantially disparate manners, both spatially and temporal, of heating the ambient medium. These differences are expected to have relevant implications on the star formation rates of the host galaxies and their evolution.

Propagation, cocoon formation, and resultant destabilization of relativistic jets

“…Then, time averagely, the pressure of the jet coincides with that of the cocoon due to the confinement of the jet by the cocoon. The internal energy and mass of the cocoon garnered through the reverse shock during the jet injection time, t, thus are estimated, when all the physical quantities characterizing the jet, such as jet radius, density, pressure, velocity, and Lorentz factor, are treated as the "temporally averaged" values, as follows: (Martí et al 1997;Bromberg et al 2011;Perucho et al 2017), where subscripts j and c stand for the jet and cocoon respectively. Here, V c is the volume of the cocoon, r j is the jet radius, h := 1 + ΓP/(Γ − 1)ρc 2 is the dimensionless specific enthalpy and v h is the propagation velocity of the jet head.…”

Simulations of the dynamics of magnetized jets and cosmic rays in galaxy clusters

“…Subsequent hydrodynamical (HD) simulations started inflating bubbles self-consistently via a subgrid jet model (Sternberg & Soker 2008). On these scales, the jet is assumed to be sufficiently slow such that nonrelativistic HD can be used (but see Perucho et al 2017). A propagating jet introduces significant heating through the dissipation of the accompanying bow shock (e.g., Reynolds et al 2002;.…”

Radio source evolution and the interplay with the host galaxy

“…Actually, a large portion of the injected energy through the jet channel is transferred to the ambient medium. In reference [20], the authors showed that this is directly related to the relativistic nature of AGN jets. The concentration of high energy and momentum fluxes through a narrow channel favours high post-shock pressure:…”