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We investigate the optical emission-line flux ratios of narrow-line regions,in order to determine whether the formation of AGN jets requires specificaccretion conditions. We find that bright compact radio galaxies, which arepowerful radio galaxies in the early stage of the jet activity, exhibitsystematically larger flux ratios of [O{\sc i}]$\lambda$6300/[O{\sciii}]$\lambda$5007 and smaller flux ratios of [O{\sc iii}]$\lambda$5007/[O{\sciii}]$\lambda$4363 than radio-quiet (RQ) Seyfert 2 galaxies. Comparing theobserved line ratios with photoionization models, it is found that thedifference in the flux ratio of low- to high-ionization lines (e.g., [O{\sci}]$\lambda$6300/[O{\sc iii}]$\lambda$5007) can be well understood by thedifference in the spectral energy distribution (SED) of ionizing sources.Powerful young radio-loud (YRL) AGNs favor SED without a strong big blue bump,i.e., a radiatively inefficient accretion flow (RIAF), while RQ AGNs areconsistent with the models adopting SED with a strong big blue bump, i.e., ageometrically thin, optically thick disk. These findings imply that theformation of powerful AGN jets requires the accretion disk with harder ionizingSED (i.e., a RIAF). We discuss the obscuring structure of YRL AGNs as aplausible origin of the difference in flux ratios of [O{\sc iii}]$\lambda$5007/[O{\sc iii}]$\lambda$4363.

Exploring the disk-jet connection from the properties of narrow line regions in powerful young radio-loud AGNs