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: ISM

galaxies: active

Författare

T. Izumi

University of Tokyo

K. Kohno

Research Center for the Early Universe

University of Tokyo

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

D. Espada

National Astronomical Observatory of Japan

The Graduate University for Advanced Studies (SOKENDAI)

Atacama Large Millimeter-submillimeter Array (ALMA)

K. Fathi

Stockholm Observatory

N. Harada

Academia Sinica

B. Hatsukade

National Astronomical Observatory of Japan

P. Y. Hsieh

Academia Sinica

National Central University Taiwan

M. Imanishi

National Astronomical Observatory of Japan

The Graduate University for Advanced Studies (SOKENDAI)

M. Krips

Institut de RadioAstronomie Millimetrique (IRAM)

S. Martin

European Southern Observatory Santiago

Atacama Large Millimeter-submillimeter Array (ALMA)

Institut de RadioAstronomie Millimetrique (IRAM)

S. Matsushita

Academia Sinica

D. S. Meier

New Mexico Institute of Mining and Technology

N. Nakai

University of Tsukuba

K. Nakanishi

National Astronomical Observatory of Japan

The Graduate University for Advanced Studies (SOKENDAI)

Atacama Large Millimeter-submillimeter Array (ALMA)

E. Schinnerer

Max-Planck-Gesellschaft

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 1 42

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

DOI

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

Mer information

Senast uppdaterat

2019-09-10