Infrared fluorescence of H2 in NGC 6240 - A starburst origin for the H2 luminosity

Journal Article · Sat Jun 01 04:00:00 EDT 1991 · Astrophysical Journal; (United States)

DOI:https://doi.org/10.1086/170140· OSTI ID:5261416

Tanaka, Masuo; Hasegawa, Tetsuo; Gatley, Ian ^[1]

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1. Tokyo, University, Mitaka (Japan) National Optical Astronomy Observatories, Tucson, AZ (USA)

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.

• OSTI ID: 5261416
• Journal Information: Astrophysical Journal; (United States), Journal Name: Astrophysical Journal; (United States) Vol. 374; ISSN ASJOA; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BASIC INTERACTIONS
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
ELEMENTS
FLUORESCENCE
GALAXIES
GRAVITATIONAL INTERACTIONS
H2 REGIONS
HYDROGEN
INFRARED RADIATION
INTERACTIONS
LUMINESCENCE
LUMINOSITY
MASS
NEAR INFRARED RADIATION
NONMETALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
STAR EVOLUTION
STARS