The unified scenario of accretion and jet physics: blazars and radio galaxies

In this thesis, we analysed radio and $\gamma$-ray data, and presented new insights and evidence supporting the unified accretion-ejection scenario between blazars and radio galaxies, based on three studies: 1. In the first study, we applied the Support Vector Machine (SVM) algorithm to classify blazars in different parameter spaces: $\gamma$-ray luminosity versus $\gamma$-ray photon index, Compton dominance versus $\gamma$-ray photon index, and disc accretion rate versus $\gamma$-ray photon index. The results show that SVM classification can effectively separate BL Lacs and FSRQs: BL Lacs are characterised by low accretion rates with synchrotron self-Compton emission, while FSRQs are characterised by high accretion rates with external Compton emission. This separation is consistent with the distinction between LERGs and HERGs, supporting the unification of BL Lacs-LERGs and FSRQs-HERGs within the accretion-ejection scenario. 2. In the second study, we demonstrated that the total accretion rate emerges as a fundamental parameter governing the intrinsic core dominance, radio morphology and disc properties in RLAGNs. In particular, LERGs show more affinity with the BL Lac population in both the higher core dominance and lower total accretion rates, supporting the BL Lacs and LERGs unification from the accretion-ejection scenario. A stratified jet model (a slower layer surrounding a faster spine) from the unified scheme is involved between LERGs and BL Lacs to constrain the Doppler factors, and interestingly, FR 0 LERGs with the large core dominances tend to exhibit lower Doppler factors than FR I/II LERGs. 3. In the third study, we explored the connection between accretion disc structures and jet formation mechanisms, and found consistent disc structures (advection-dominated accretion flows, ADAFs) and Blandford-Znajek (BZ) jet formation mechanisms for both BL Lacs and LERGs. Moreover, FR 0 LERGs share remarkable similarities with high-synchrotron-peaked BL Lacs (HBLs) in terms of their environments, ADAF disc structures, and BZ jet mechanisms. Assuming a close link between radio cores and $\gamma$-ray emission, we predict possible $\gamma$-ray emission from the currently undetected $\gamma$-ray FR 0 LERGs, construct their spectral energy distributions, and compare them with the sensitivities of the Fermi Large Area Telescope, and Cherenkov Telescope Array Observatory. In conclusion, based on the multi-band approach from radio to $\gamma$-ray, these three studies collectively place blazars and radio galaxies within a unified accretion-ejection framework. The results not only strengthen the intrinsic physical connections between the two populations, such as disc structures, accretion rates, high-energy radiation mechanisms, and jet formation processes, but also provide new perspectives for understanding the unification of RLAGNs and knowledge for accretion-ejection physics in RLAGNs.