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Register a new userObservational constraints on the cosmological evolution of dual-population radio sources
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M. Jamrozy
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In this paper we show normalized differential source counts n(S) at 408 MHz and 1.4 GHz of radio sources separately for FRI and FRII classes with extended and compact morphologies. The maps from the FIRST, NVSS, and WENSS surveys are used to define the source morphology and flux density. The counts provide a basis for a direct test as well as constraining the cosmological evolution of powerful extragalactic radio sources in terms of the dual-population model (Jackson & Wall 1999), where radio sources of Fanaroff-Riley (1974) types I and II are regarded as two physically separate types of active galactic nuclei (AGN). The predicted count values are compared with the observational data to find the best fits for the evolution and beaming parameters, and to further refine the model.
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We present an analytical model for the cosmological evolution of the FRII source population. Based on an earlier model for the intrinsic radio luminosity - linear size evolution of these objects, we construct theoretical source samples. The source distributions in the radio power - linear size plane of these samples are then compared with that of an observed flux-limited sample. We find that the source parameters determining the radio luminosity of FRII objects can not be independent of each other. The best-fitting models predict the jet power to be correlated either with the life time of the source or with the shape of the density distribution of the source environment. The latter case is consistent with the observed tendency of the most luminous radio sources at high redshift to be located in richer and more extended environments than their low redshift counterparts. We also find evidence for a class of FRII sources distinctly different from the main population. These sources are extremely old and/or are located in very underdense environments. The luminosity function of FRII sources resulting from the model is in good agreement with previous results for high luminosity sources. The apparent luminosity evolution of the radio luminosity function is not reproduced because of the high flux limit of the used comparison sample. The cosmological evolution of the median linear size of FRII sources is found to be mild.
Over the last years some interest has been gathered by $f(Q)$ theories, which are new candidates to replace Einsteins prescription for gravity. The non-metricity tensor $Q$ allows to put forward the assumption of a free torsionless connection and, consequently, new degrees of freedom in the action are taken into account. This work focuses on a class of $f(Q)$ theories, characterized by the presence of a general power-law term which adds up to the standard (linear in) $Q$ term in the action, and on new cosmological scenarios arising from them. Using the Markov chain Montecarlo method we carry out statistical tests relying upon background data such as Type Ia Supernovae luminosities and direct Hubble data (from cosmic clocks), along with Cosmic Microwave Background shift and Baryon Acoustic Oscillations data. This allows us to perform a multifaceted comparison between these new cosmologies and the (concordance) $Lambda$CDM setup. We conclude that, at the current precision level, the best fits of our $f(Q)$ models correspond to values of their specific parameters which make them hardly distinguishable from our General Relativity echantillon, that is $Lambda$CDM.
The time evolution of giant (D>1 Mpc) lobe-dominated galaxies is analysed on the basis of dynamical evolution of the entire FRII-type population.
The time evolution of giant lobe-dominated radio galaxies (with projected linear size D>1 Mpc if H_{0}=50 km/s/Mpc and q_{0}=0.5 is analysed on the basis of dynamical evolution of the entire FRII-type population. Two basic physical parameters, namely the jet power Q_{0} and central density of the galaxy nucleus rho0 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, Q_{0} and rho_{0} are obtained by fitting the dynamical model of Kaiser et al. (1997). We find that: (i) there is not a unique factor governing the source size; they are old sources with temperate jet power (Q_{0}) evolved in a relatively low-density environment (rho_{0}). The size is dependent, in order of decreasing partial correlation coefficients, on age; then on Q_{0}; next on rho_{0}. (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.
This paper reviews some of the observational properties of globular cluster systems, with a particular focus on those that constrain and inform models of the formation and dynamical evolution of globular cluster systems. I first discuss the observational determination of the globular cluster luminosity and mass function. I show results from new very deep HST data on the M87 globular cluster system, and discuss how these constrain models of evaporation and the dynamical evolution of globular clusters. The second subject of this review is the question of how to account for the observed constancy of the globular cluster mass function with distance from the center of the host galaxy. The problem is that a radial trend is expected for isotropic cluster orbits, and while the orbits are observed to be roughly isotropic, no radial trend in the globular cluster system is observed. I review three extant proposals to account for this, and discuss observations and calculations that might determine which of these is most correct. The final subject is the origin of the very weak mass-radius relation observed for globular clusters. I discuss how this strongly constrains how globular clusters form and evolve. I also note that the only viable current proposal to account for the observed weak mass-radius relation naturally affects the globular cluster mass function, and that these two problems may be related.
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