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2 Acta Astronomica

2 2004

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Giant Radio Sources in View of the Dynamical Evolution of FRII-type Population. I. The Observational Data and Basic Physical Parameters of Sources Derived from the Analytical Model

Machalski J., Chyży K. T., Jamrozy M.

Acta Astronomica

2004

Vol. 54, No. 3

249--279

The time evolution of giant lobe-dominated radio galaxies (with projected linear size D>1 Mpc if H0=50 km/s Mpc and q0=0.5) is analyzed on the basis of dynamical evolution of the entire FRII-type population. Two basic physical parameters, namely the jet power Q0 and central density of the galaxy nucleus ρ0 are derived for a sample of giants with synchrotron ages reliably determined, and compared with the relevant parameters in a comparison sample of normal-size sources consisting of 3C, B2, and other sources. Having the apparent radio luminosity P and linear size D of each sample source, Q0 and ρ0 are obtained by fitting the dynamical model of Kaiser et al. We find that: (i) There is no unique factor governing the source size. The sources are old, with temperate jet power (Q0) and are evolved in a relatively low-density environment (ρ0). The size is dependent, in order of decreasing partial correlation coefficients, on age, then on Q0, next on ρ0. (ii) A self-similar expansion of the sources' cocoon seems to be feasible if the power supplied by the jets is a few orders of magnitude above the minimum-energy value. In other cases the expansion can only initially be self-similar, a departure from self-similarity for large and old sources is justified by observational data of giant sources. (iii) An apparent increase of the lowest internal pressure value observed within the largest sources' cocoon with redshift is obscured by the intrinsic dependence of their size on age and the age on redshift, which hinders us from making definite conclusions about a cosmological evolution of intergalactic medium (IGM) pressure.

Giant Radio Sources in View of the Dynamical Evolution of FRII-Type Population. II. The Evolutionary Tracks on the P-D and uc - Etot Planes

Machalski J., Chyży K. T., Jamrozy M.

Acta Astronomica

2004

Vol. 54, No. 4

391--403

The time evolution of "fiducial" radio sources derived from fitting the dynamical model of Kaiser et al. (1997) is compared with the observational data for the "clan" sources found in the sample of giant and normal-size FRII-type sources published in Paper I (Machalski et al. 2004). Each "clan" comprises 3, 4 or 5 sample sources having similar values of the two basic physical parameters: the jet power Q0 and central density of the galaxy nucleus ρ0 (determined in Paper I) but different ages, radio luminosities and axial ratios. These sources are considered as the "same" source observed at different epochs of its lifetime and used to fit the evolutionary luminosity-size (P-D) and energy density-total energy (uc-Etot) tracks derived from the model for a "fiducial" source with Q0 and ρ0 equal to the averages of relevant values obtained for the "clan" members, as well as to constrain the evolutionary model of the source dynamics used. In the result we find that (i) the best fit is achieved when the Kaiser et al.'s model is modified by allowing an evolution of the sources' cocoon axial ratio with time as suggested by Blundell et al. (1999), (ii) a slow acceleration of the average expansion speed of the cocoon along the jet axis is suggested by the "clan" sources. We argue that this acceleration, although minor, may be real and some supporting arguments come from the well known hydrodynamical considerations.