Infrared fluorescence of H2 in NGC 6240 : a starburst origin for the H2 luminosity

It is shown here that the published emission line ratios for vibrationally excited molecular hydrogen in the near-IR for the highly luminous galaxy merger system NGC 6240 imply UV excitation followed by IR fluorescence. The line ratios for the central 2 kpc or so of the system are well-reproduced as...

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Bibliographic Details
Published inThe Astrophysical journal Vol. 374; no. 2; pp. 516 - 521
Main Authors TANAKA, M, HASEGAWA, T, GATLEY, I
Format Journal Article
LanguageEnglish
Published Chicago, IL University of Chicago Press 01.06.1991
Subjects
640105 - Astrophysics & Cosmology- Galaxies
Astronomy
BASIC INTERACTIONS
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
COSMIC RADIO SOURCES
Earth, ocean, space
ELECTROMAGNETIC RADIATION
ELEMENTS
Exact sciences and technology
FLUORESCENCE
GALAXIES
GRAVITATIONAL INTERACTIONS
H2 REGIONS
HYDROGEN
INFRARED RADIATION
INTERACTIONS
LUMINESCENCE
LUMINOSITY
MASS
NEAR INFRARED RADIATION
NONMETALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
Quasars. Active or peculiar galaxies, objects, and systems
RADIATIONS
STAR EVOLUTION
STARS
Stellar systems. Galactic and extragalactic objects and systems. The universe
Molecular process
Galactic activity
Merging galaxies
Data analysis
Radiation mechanism
Hydrogen Molecules
Fluorescence
Interating galaxies
Data table
Infrared radiation
Infrared spectrum
Interstellar molecule
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Summary:It is shown here that the published emission line ratios for vibrationally excited molecular hydrogen in the near-IR for the highly luminous galaxy merger system NGC 6240 imply UV excitation followed by IR fluorescence. The line ratios for the central 2 kpc or so of the system are well-reproduced as a mixture of fluorescent and thermal components. Of the total H2 luminosity of 3 {times} 10 to the 9th solar, 70 percent is due to fluorescence. This emission is excited by UV photons probably radiated by many early B stars. The abundance of such stars and the deficit of O stars indicate a sharp upper mass cutoff at about 20 solar masses in the present-day mass spectrum in the central region. A starburst model is presented in which the observations can be reproduced if the central region experienced a cataclysmic starburst which stopped suddenly a few ten billion yr ago and if the initial mass function there had a lower mass cutoff at about 5 solar. 31 refs.
ISSN:0004-637X
1538-4357
DOI:10.1086/170140