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SUBMILLIMETER-HCNDIAGRAM FOR ENERGYDIAGNOSTICS IN THECENTERS OF GALAXIES Takuma IzumiKotaro KohnoS. Aalto2016 год

SUBMILLIMETER-HCN DIAGRAM FOR ENERGY DIAGNOSTICS IN THE CENTERS OF GALAXIES
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Аннотация: ABSTRACT Compiling data from literature and the Atacama Large Millimeter/submillimeter Array archive, we show enhanced HCN(4–3)/HCO + (4–3) and/or HCN(4–3)/CS(7–6) integrated intensity ratios in circumnuclear molecular gas around active galactic nuclei (AGNs) compared to those in starburst (SB) galaxies (submillimeter HCN enhancement). The number of sample galaxies is significantly increased from our previous work. We expect that this feature could potentially be an extinction-free energy diagnostic tool of nuclear regions of galaxies. Non-LTE radiative transfer modelings of the above molecular emission lines involving both collisional and radiative excitation, as well as a photon trapping effect, were conducted to investigate the cause of the high line ratios in AGNs. As a result, we found that enhanced abundance ratios of HCN to HCO + and HCN to CS in AGNs as compared to SB galaxies by a factor of a few to even ≳10 are a plausible explanation for the submillimeter HCN enhancement. However, a counterargument of a systematically higher gas density in AGNs than in SB galaxies can also be a plausible scenario. Although we cannot fully distinguish these two scenarios at this moment owing to an insufficient amount of multi-transition, multi-species data, the former scenario is indicative of abnormal chemical composition in AGNs. Regarding the actual mechanism to realize the composition, we suggest that it is difficult with conventional gas-phase X-ray-dominated region ionization models to reproduce the observed high line ratios. We might have to take into account other mechanisms such as neutral–neutral reactions that are efficiently activated in high-temperature environments and/or mechanically heated regions to further understand the high line ratios in AGNs.
Год издания: 2016
Авторы: Takuma Izumi, Kotaro Kohno, S. Aalto, D. Espada, Kambiz Fathi, Nanase Harada, Bunyo Hatsukade, Pei‐Ying Hsieh, Masatoshi Imanishi, Melanie Krips, S. Martín, Satoki Matsushita, David S. Meier, Naomasa Nakai, Kouichiro Nakanishi, E. Schinnerer, Kartik Sheth, Yuichi Terashima, Jean L. Turner
Издательство: IOP Publishing
Источник: The Astrophysical Journal
Ключевые слова: Astrophysics and Star Formation Studies, Galaxies: Formation, Evolution, Phenomena, Stellar, planetary, and galactic studies
Другие ссылки: The Astrophysical Journal (HTML)
arXiv (Cornell University) (PDF)
arXiv (Cornell University) (HTML)
Chalmers Publication Library (Chalmers University of Technology) (PDF)
Chalmers Publication Library (Chalmers University of Technology) (HTML)
DataCite API (HTML)