Vibrationally excited HCN in the luminous infrared galaxy NGC 4418
Artikel i vetenskaplig tidskrift, 2010

Infrared pumping and its effect on the excitation of HCN molecules can be important when using rotational lines of HCN to probe dense molecular gas in galaxy nuclei. We report the first extragalactic detection of (sub)millimeter rotational lines of vibrationally excited HCN, in the dust-enshrouded nucleus of the luminous infrared galaxy NGC 4418. We estimate the excitation temperature of T-vib approximate to 230 K between the vibrational ground and excited (v(2) = 1) states. This excitation is most likely due to infrared radiation. At this high vibrational temperature the path through the v(2) = 1 state must have a strong impact on the rotational excitation in the vibrational ground level, although it may not be dominant for all rotational levels. Our observations also revealed nearly confusion-limited lines of CO, HCN, HCO+, (HCN)-C-13, (HCN)-N-15, CS, N2H+, and HC3N at lambda similar to 1 mm. Their relative intensities may also be affected by the infrared pumping.

vib-rotational transitions


molecular gas

galaxies: ISM


galaxies: individual (NGC 4418)

galaxies: active





einstein a-coefficients



K. Sakamoto

Academia Sinica

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

A. S. Evans

National Radio Astronomy Observatory

University of Virginia

M. C. Wiedner

Observatoire de Paris

D. J. Wilner

Harvard-Smithsonian Center for Astrophysics

Astrophysical Journal Letters

2041-8205 (ISSN) 2041-8213 (eISSN)

Vol. 725 2 L228-L233


Astronomi, astrofysik och kosmologi



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