Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7977z&link_type=abstract
HST Proposal ID #7977
Astronomy and Astrophysics
Astrophysics
Hst Proposal Id #7977 Extragalactic Astrophysics
Scientific paper
Based on the archival FOS data we constructed a composite quasar spectrum and found that the continuum between ~ 350 Angstrom and 1000 Angstrom can be approximated with a power law of f_Nu propto nu^-1.8 which may well connect with the soft X-ray flux level. However, uncertainties were significant at shorter wavelengths as the number of high-z quasars in the merged spectrum was small. A database of all FOS spectra, plus some archival STIS spectra, will increase the number of z > 1.5 quasars by nearly an order of magnitude. Accurate measurements of the quasar EUV continuum will be used to derive the shape of the UV background field in the early universe. In particular, the redshift dependence of the quasar continuum shape between z ~ 1.0 and 4.0 will offer a key input to models of the intergalactic medium. The results will also be used to improve photoionization calculations for AGN and to search for new EUV emission lines. A set of composite quasar continua at different redshifts and with different radio properties will be made available to the astronomy community.
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