On the extragalactic nature of the far-ultraviolet background

Details On the extragalactic nature of the far-ultraviolet background On the extragalactic nature of the far-ultraviolet background

Jan 1980

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980a%26a....81...66j&link_type=abstract

Astronomy and Astrophysics, vol. 81, no. 1-2, Jan. 1980, p. 66-73. Research supported by the Danish Space Board.

Astronomy and Astrophysics

Astronomy

18

Background Radiation, Far Ultraviolet Radiation, Intergalactic Media, Ultraviolet Astronomy, Absorption Spectra, Helium, Quasars, Red Shift, Seyfert Galaxies

Scientific paper

It is argued that if the far ultraviolet (FUV) background 'hump' observed near lambda 1450 A at high galactic latitudes is due to redshifted He II 304 emitted by an Intergalactic Medium (IGM) at redshift z is approximately equal to 3.08, the strength and width of this feature suggest that collisional excitation is the exciting mechanism. This again implies the existence of intergalactic He II in the redshift interval between 3.4 and 4.1 which can possibly be seen in absorption in the FUV-spectra of the highest redshift quasars such as OQ 172 (z = 3.53). It is also emphasized that the IGM does not necessarily have to be dense and smoothly distributed in order to produce this radiation. In particular it is shown that the Weymann (1967) scheme for IGM reheating, which predicts the presence of a redshifted He II 304 FUV background feature similar to that observed, can only be made consistent with other observations provided that the IGM is kept cool between 1000 and 100,000 K and is highly clumped. A rough estimate of the 1450 A background contributions due to normal galaxies, Seyfert galaxies and quasars suggests that these objects supply less than 10% of the observed background intensity.

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