Diffuse component of the cosmic far UV radiation and interstellar dust grains

Abstract

The diffuse far UV radiation (λλ 1350–1480 Å) observed in the sky region ofl ^II≈180°, 0°≤b ^II≲40° is analyzed in connection with the distributions of stars and dust grains as well as with optical properties of grains. Its intensity (starlight+scattered light) is about 6×10⁻⁷ erg cm⁻² sec⁻¹ sr⁻¹ Å⁻¹ in the direction ofb ^II≈0° andl ^II≈180°. The latitude dependence of the intensity is in approximate agreement with the plane parallel slab model of the galaxy with a reasonable set of parameters. The interstellar scattering gives an albedo close to unity and forward phase function of about 0.6, which are not inconsistent with the model of interstellar grains of Wickramasinghe. The upper limit of the extragalactic UV is 2×10⁻⁸ erg cm⁻² sec⁻¹ sr⁻¹ Å⁻¹ in the same region of wave-length.