SUBMILLIMETER-HCN DIAGRAM FOR ENERGY DIAGNOSTICS IN THE CENTERS OF GALAXIES
Artikel i vetenskaplig tidskrift, 2016

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 greater than or similar to 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.

ISM: molecules

galaxies: active

galaxies: ISM

Författare

T. Izumi

University of Tokyo

K. Kohno

University of Tokyo

Research Center for the Early Universe

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

D. Espada

The Graduate University for Advanced Studies (SOKENDAI)

National Institutes of Natural Sciences - National Astronomical Observatory of Japan

Atacama Large Millimeter-submillimeter Array (ALMA)

K. Fathi

Stockholm Observatory

N. Harada

Academia Sinica

B. Hatsukade

National Institutes of Natural Sciences - National Astronomical Observatory of Japan

P. Y. Hsieh

Academia Sinica

National Central University Taiwan

M. Imanishi

National Institutes of Natural Sciences - National Astronomical Observatory of Japan

The Graduate University for Advanced Studies (SOKENDAI)

M. Krips

Institut de RadioAstronomie Millimetrique (IRAM)

S. Martin

Atacama Large Millimeter-submillimeter Array (ALMA)

Institut de RadioAstronomie Millimetrique (IRAM)

European Southern Observatory Santiago

S. Matsushita

Academia Sinica

D. S. Meier

New Mexico Institute of Mining and Technology

N. Nakai

University of Tsukuba

K. Nakanishi

Atacama Large Millimeter-submillimeter Array (ALMA)

The Graduate University for Advanced Studies (SOKENDAI)

National Institutes of Natural Sciences - National Astronomical Observatory of Japan

E. Schinnerer

Max Planck-institutet

K. Sheth

National Aeronautics and Space Administration

Y. Terashima

Ehime University

J. L. Turner

University of California

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 818 42

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

DOI

10.3847/0004-637x/818/1/42