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THE CASE FOR AN EXTRAGALACTIC ORIGIN FOR THE HIGH GALACTIC LATITUDE DIFFUSE ULTRAVIOLET BACKGROUND
 

Summary: THE CASE FOR AN EXTRAGALACTIC ORIGIN FOR THE HIGH
GALACTIC LATITUDE DIFFUSE ULTRAVIOLET BACKGROUND
Richard C. Henry and Jayant Murthy
Center for Astrophysical Sciences
Henry A. Rowland Department of Physics and Astronomy
The Johns Hopkins University
Baltimore, MD 21218
Abstract. A simple model is presented which can be used to predict the diffuse background that is to be
expected at high galactic latitudes due to the light of galactic plane OB stars scattered from high latitude
dust. When combined with a recent and highly reliable determination of the scattering pattern of
interstellar grains in the far ultraviolet, this model indicates that such scattering cannot account for the
continuous spectrum that is seen at high latitudes by all observers. The spectrum of the extragalactic
background is ~ flat longward of 1216 and is undetected shortward of that wavelength, suggesting an
origin in hydrogen recombination radiation, although the intensity is higher than is expected in common
cosmological models (Henry 1991).
There is considerable dust at high galactic latitudes; for example Hauser et al. (1984) report, from
their study of IRAS cirrus observations, that Av = 0.1 mag at high latitudes. (We use that value, which is
probably too high by at least a factor two, in order to be conservative in our conclusions.) Also, there are
many bright OB stars in or near the galactic plane (Fig. 1). For our simple model for the scattered light of
these stars, we integrate the Henyey-Greenstein (1941) scattering function

  

Source: Henry, Richard C.- Department of Physics and Astronomy, Johns Hopkins University

 

Collections: Physics