Quest on Yong Radio Galaxies Using Space-VLBI

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We aimed a statistical study for environments of young radio galaxies via observations for their spectrum and size. Free-Free Absorption (FFA) process is used as a probe into cold dense plasma surrounding radio galaxies. Space-VLBI observations provides a sub-pc-scale resolution for the spatial distribution of the FFA opacities.We discovered a 1-pc plasma torus around the nucleus of a radio galaxy NGC 1052, which is one of our samples. The FFA opacity marks maximum towards the nucleus. The electron density and temperature measured 2.5 × 10^4【less than or equal】 n_c 【less than or equal】 2.6 × 10^6 cm^<-3> and 10^4 【less than or equal】 T_e 【less than or equal】 4.9 × 10^6 K, respectively. The opacity tapers along the western receding jet over 1 pc, while it is cut down at 0.1 pc from the nucleus to the eastern approaching jet. The opaque region towards the western jet coincides where H_2O maser spots are. The velocity gradient of masers indicates that molecules inside the torus accrete to the nucleus by 〜 200 km s^<-1>. These results are reported in Karneno et al. 2003, PASA, 20, No.1 in press.Our pentachromatic survey for 18 young radio galaxies revealed that significant difference between young radio galaxies and quasars, in terms of distribution of FFA opacities. While young radio galaxies tend to show symmetric FFA opacities towards double lobes, the opacities towards young quasars are asymmetric. The apparent difference can be explained by the unified scheme (Barthel 1989, ApJ, 336, 606), which claims that quasars and radio galaxies are intrinsically the same but apparently different by small and large viewing angles, respectively. A small viewing angle produces different path length through cold dense plasma surrounding the lobes and hence causes asymmetric FFA opacities. The report on the results was submitted to PASA.