Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apjs..141..371c&link_type=abstract
The Astrophysical Journal Supplement Series, Volume 141, Issue 2, pp. 371-414.
Astronomy and Astrophysics
Astronomy
29
Galaxies: Jets, Hydrodynamics, Galaxies: Intergalactic Medium, Radio Continuum: Galaxies
Scientific paper
We present two-dimensional numerical hydrodynamical simulations of light, supersonic jets propagating in atmospheres that decline in density with increasing distance in several ways: isothermal King law atmospheres with the power-law exponent β=1 and β=0.75 and in an isobaric King law atmosphere with power-law exponent β=1. We explore the same very broad range of parameter space in Mach number M and density contrast η as in Paper I in this series. We compare our results with those for the constant density and pressure atmosphere simulations and with the predictions of the self-similar models (Paper I). We also discuss the global energetics of the sources in these different environments. Our comparison of the constant and declining density results shows the following. The overall morphology of the jet, cocoon, and bow shock is similar. However, there are some differences that start to appear when the jet has propagated about twice the core radius. In a declining density atmosphere, (1) there is less structure in the cocoon as a result of turbulence and (2) at a given source size, the cocoon seems to be underexpanded relative to a constant density atmosphere for a broad range of Mach numbers ~5-30 (outside this range the cocoon may actually be wider). In an isobaric atmosphere with density gradient the general appearance of the source is similar to that of an isothermal atmosphere although the source size increases much faster. The overall distribution of pressure in the shocked ambient gas (SAG) region and cocoon and its decline with distance from the jet head are similar in both types of atmospheres. However, in jets in declining density atmospheres, for case 1 (pressure dominated by relativistic electrons), the cocoon and SAG region remain much more overpressured with respect to the ambient medium than in jets in constant density atmospheres. The lateral expansion speeds of the bow shock and cocoon are similar in the constant and declining density atmospheres. In a constant density atmosphere the jet head velocity decelerates slowly with time, while in the declining density atmosphere the jet head accelerates with time with a rate given by exponent zh~tm with 1
Carvalho Joel C.
O'Dea Christopher P.
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