Published in "Extragalactic Background Radiation", Space Telescope Science Institute Symposium Series 7, 1995, eds. D. Calzetti, M. Livio and P. Madau


EXTRAGALACTIC ULTRAVIOLET BACKGROUND RADIATION

Richard C. Henry


Center for Astrophysical Sciences, Henry A. Rowland Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218
and
Space Astronomy and Astrophysics Group, Los Alamos National Laboratory

Jayant Murthy


Center for Astrophysical Sciences, Henry A. Rowland Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218


Abstract. We describe observations of the cosmic background in the far ultraviolet. If the Voyager upper limit on the cosmic diffuse ultraviolet background at 1100 Å at some locations is accepted as correct, the spectrum of the high-galactic latitude background is most remarkable, featuring an abrupt rise at about 1216 Å. Such a rise suggests an origin in redshifted Lyman alpha recombination radiation, but that explanation requires the existence of an ionization source such as the radiative decay of massive neutrinos to maintain the ionization. We therefore explore a more conservative origin in the scattered light of galactic plane OB stars. This explanation is fraught with difficulties: a dust population specially invented for the purpose seems to be required. This ad hoc explanation may be preferred by some; a perhaps somewhat exotic extragalactic origin by others. Quite simple additional observations should clarify matters considerably.


Table of Contents

INTRODUCTION

THE ULTRAVIOLET BACKGROUND AT HIGH LATITUDE

OBSERVATIONS OF DIFFUSE BACKGROUND GENERALLY

LINE EMISSION FROM THE INTERSTELLAR MEDIUM

STARLIGHT SCATTERING FROM INTERSTELLAR DUST

VOYAGER OBSERVATIONS OF THE DIFFUSE BACKGROUND

DISCUSSION

CONCLUSION

REFERENCES

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