Very Light Jets I. Axisymmetric Parameter Study and Analytic Approximation

TL;DR

This study combines numerical simulations and analytic models to analyze the propagation of very light extragalactic jets across various density regimes, revealing insights into bow shock behavior and implications for young radio galaxies.

Contribution

It extends previous models by providing a comprehensive analytic solution for spherical bow shock phases and explores the impact of different density profiles on jet propagation.

Findings

Bow shocks are spherical below a critical size, up to 10 jet radii.

Analytic models agree with numerical simulations, allowing for predictions of shock behavior.

Powerful jets can transfer significant energy to their environment, influencing galaxy cluster dynamics.

Abstract

The propagation of extragalactic jets is studied by a series of twelve axisymmetric hydrodynamic simulations. Motivated by observational constraints, but unlike most previous simulations, the regime of jet to external medium density (eta) from 10^-5 to 10^-2 is explored, for Mach numbers (M) between 2.6 and 26. The computational domain contained the bow shocks for the whole simulation time. The bow shocks are found to be spherical at source sizes below a critical value r1 (blastwave phase), which can reach up to 10 jet radii. [...] The numerical work is complemented by an analytic approach for the spherical phase. Extending previous work, the radial force balance could be integrated for arbitrary background density and energy input, which results in a global solution. The analytic results are shown to be consistent with the numerical work, and a lower limit to r1 can be calculated, which falls below the numerical results by a few jet radii. It is shown explicitely how a King density distribution changes the discussed aspects of the bow shock propagation. Because the jet head propagates very fast in the blastwave phase, it turns out that it is not possible to ``frustrate'' a jet by a high density environment. This is very important for the class of small radio galaxies (compact symmetric objects / GHz peaked sources): They have to be young. During its blastwave phase, a powerful jet can transfer typically 10^60 erg to the environmental gas. This is enough to balance the radiative losses in a cooling flow, if one of the cluster galaxies harbours a powerful jet every Gigayear.