Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...454l..19l&link_type=abstract
Astrophysical Journal Letters v.454, p.L19
Astronomy and Astrophysics
Astronomy
214
Galaxies: Intergalactic Medium, Galaxies: Ism, Galaxies: Starburst, Ultraviolet: Galaxies
Scientific paper
The starburst galaxies IRAS 08339+6517, Mrk 1267, Mrk 66, and Mrk 496 (=NGC 6090) were observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 mission. All four galaxies have radial velocities larger than 5000 km s-1, permitting the measurement of their intrinsic Lyman-continuum fluxes redward of the H I absorption edge in our Galaxy. The sample was selected on the basis of having the most favorable conditions for the escape of Lyman-continuum photons. Two sigma upper limits of F lambda < 7 x 10-16 ergs s-1 cm-2 A-1 were obtained for the flux around 900 A within the rest frame of each galaxy. A set of theoretical spectral energy distributions has been calculated. We show that there exists a tight correlation between the continuum luminosity at 900 A and the total number of photons emitted in the Lyman continuum, which is valid for high- and low-metallicity galaxies and essentially all relevant initial mass functions and star formation histories. Comparison with the observed values suggests that, on average, less than 3% of the intrinsic Lyman-continuum photons escape from the program galaxies. Models for the ionization of the intergalactic medium at high z by young starbursts require a significant fraction of the ionizing radiation to escape from the galaxy. If the four galaxies observed by us have properties similar to young galaxies at redshift z ~ 3, such galaxies are not likely to provide Lyman-continuum photons for the ionization of the early universe.
Ferguson Henry C.
Heckman Timothy M.
Leitherer Claus
Lowenthal James D.
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