Observations And Research Of Compact Symmetric Objects

Compact symmetric objects(CSOs) have been found to be young radio sources that they are probably in the early evolutionary stage of large double-lobed radio source. Since most of CSOs have not shown strong beaming effect, using Very Long Baseline Interferometry (VLBI), one could obtain more intrinsic information about the radio structure in the active galactic nuclei (AGNs).In Chapter 1, the basic concepts of VLBI were briefly described. The separation speed between two lobes and the age of the radio structure in one of CSOs, OQ208, are presented in Chapter 2, these results are based on the multi-epoch data of VLBA observations in the radio reference image database (RRFID), the estimated age of the radio structure is about 200 years, OQ208 may be one of the youngest CSO. Chapter 3 showed the results of the EVN+MERLIN observations, the aim is to check if the proposed sources have large structure and to detect new CSOs. One source 1345+125 was identified as a new CSO from the observations; We found there is the free-free absorption in the weaker radio lobe of OQ208 , which is consistent with the results from the VSOP observation. Theimage of 1751+278 shows a core-jet feature and 1604+315 is a point source at 18 cm; all 5 sources observed were not resolved with MERLIN. 5 typical high-frequency-peakers (HFPs) were observed with EVN plus few geodetic antennas, 3 of them are probably the CSO candidates, this indicates that CSO detection rate could be high in HFP sample. 1333+589 is possibly a core-jet source, because its northen component has an inverted spectrum. Chapter 4 introduced Readhead's and Fanti's models of CSOs, the differences of the models were discussed. In Chapter 5, the flux density ratio between the two lobes in 5 CSOs were investigated, the beaming effect and outer-medium-effect can explain the asymmetric flux ratio in the narrow-line CSOs, the Thomson scattering were added to explain the large flux ratio in OQ208, although the explaination needs to check in details. Chapter 6 introduced that detection rate of CSOs seems decreasing when sample size increasing, we proposed an idea for the birth of a CSO that early type Sb,c-Sb,c galaxy merging into elliptical galaxy could trigger a CSO phenomenon. Chapter 7 gave a summary of the thesis.