Summary and Future Outlook

Abstract

Outcomes of this thesis are summarized in this Chapter. We have conducted experimental mm/submm spectroscopic studies toward nearby Seyfert galaxies, in order to find links among properties of molecular gas, active galactic nuclei (AGN), and circumnuclear starburst activities (we denoted them as active trinity). We first revealed submm-HCN enhancement in active galactic nuclei (AGN) environment, i.e., enhanced HCN(4-3)/HCO$^+$(4-3) and HCN(4-3)/CS(7-6) intensity ratios, as compared to starburst galaxies. This would be due to enhanced HCN abundance in AGNs, which indicates AGN’s chemical feedback to molecular gas. Next, we theoretically investigated a detectability of submm HI recombination lines stemming from a broad line region (BLR) of an AGN, which is a robust indicator of AGN activity. However, we identified that it is highly impractical to detect that kind lines. Lastly, we probed any relationship between molecular gas properties at the circumnuclear disk (CND) scale and AGN activity. We suggested that CND-scale molecular gas is a direct source of fuel for mass accretion. The balance of mass flows (in- vs out-) could be well reproduced by a supernova-driven turbulent accretion model, although we do not discard other accretion models. Our studies then offer unique guidance on how to use the fully-operated Atacama Large Millimeter/submillimeter Array (ALMA) to make significant progress in AGN science.