QSOs or Galaxies -- The Strength of the Intergalactic Ionizing Radiation Field.

Details QSOs or Galaxies -- The Strength of the Intergalactic Ionizing Radiation Field. QSOs or Galaxies -- The Strength of the Intergalactic Ionizing Radiation Field.

May 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.4809e&link_type=abstract

American Astronomical Society, 180th AAS Meeting, #48.09; Bulletin of the American Astronomical Society, Vol. 24, p.808

Astronomy and Astrophysics

Astronomy

Scientific paper

Much effort has been put into explaining the descrepancy between the observed number of QSOs and the number of ionizing sources required to explain the strength of the intergalactic ionizing radiation field. At present it is generally believed that between 5 and 20\ be accounted for by observed QSOs. The source of the majority of the ionizing photons has been much discussed and models have been developed which attempt to explain these `additional' ionizing sources as being either hidden QSOs (with dust providing the obscuring medium) or a population of high redshift galaxies undergoing a burst of star formation. We show that most of the apparent descrepancy may be actually due to a bias in the way that the strength of the ionizing field is measured. It has been conventionally assumed that the Lyalpha \ and CIV lines lie at the rest redshift of the QSO, whereas there is convincing evidence that this is not the case. It will be shown that by using the mean velocity shift observed in a sample of QSOs of comparable luminosity to those used for UV background studies it is possible to explain most if not all of the apparent descrepancy as being due to overestimation of the strength of the background radiation field. Previous estimates of the significance of velocity shifts have been influenced by the smaller shifts seen in low luminosity, low redshift objects so this work addresses the question with data applicable to the high luminosity objects commonly used in absorption line studies. The conclusion of this work is that the existence of a large population of non-QSO ionizing sources or high redshift dusty regions is now called into question.

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