Flash-photoionized nebulae

Journal Article · Mon May 01 04:00:00 EDT 1989 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/167396· OSTI ID:5695161

Katz, J I

Under conditions of high radiation intensity and low gas density, recombination may be neglected in determining the ionization state of a photoionized gas. Calculations of the ionization structure of nebulae in this 'flash-photoionized' regime are reported. Very hard spectra of ionizing ultraviolet radiation may be produced by filtration of the ionizing flux through a neutral hydrogen layer which preferentially absorbs photons just above the hydrogen photoionization threshold. Fluxes with these hard spectra produce gas layer in which helium is largely doubly ionized while hydrogen is largely neutral. Such a layer leads to anomalously high ratios of He II to H I recombination line strengths. These results are applied to the problem of the spectrum of the arc in the cluster of galaxies A370. It is found that the spectrum may possibly be reconciled with the light echo model. 25 refs.

• Research Organization: Washington Univ., Saint Louis, MO (USA)
• OSTI ID: 5695161
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 340; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
BLACKBODY RADIATION
COSMIC GASES
CROSS SECTIONS
ELECTROMAGNETIC RADIATION
ELEMENTS
FLUIDS
FLUX DENSITY
GALAXY CLUSTERS
GASES
HELIUM
HYDROGEN
IONIZATION
IONIZING RADIATIONS
NEBULAE
NONMETALS
PHOTOIONIZATION
RADIANT FLUX DENSITY
RADIATIONS
RARE GASES
SPECTRA
SPECTROSCOPY
ULTRAVIOLET SPECTRA