A HST Composite Quasar Spectrum

Details A HST Composite Quasar Spectrum A HST Composite Quasar Spectrum

May 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aas...188.0503z&link_type=abstract

American Astronomical Society, 188th AAS Meeting, #05.03; Bulletin of the American Astronomical Society, Vol. 28, p.827

Astronomy and Astrophysics

Astronomy

Scientific paper

We construct a composite quasar spectrum from 284 HST FOS spectra of 101 quasars with a mean redshift z ~ 1. The spectrum covers the wavelengths between 350 Angstroms and 3000 Angstroms in the rest frame, with a peak S/N level of ~ 150 per Angstroms at ~ 1100 Angstroms. Since ~ 90% of the sample quasars have redshift z < 1.5, the spectrum is suitable for studying the wavelength region shortward of Lyalpha without any significant effect of intervening Lyalpha forest absorption. Data in the waveband between 350 Angstroms and 600 Angstroms are mainly from the spectra of z > 1.5 quasars, for which significant corrections for the accumulated Lyman--series line and continuum absorption have been applied. There is a significant steepening of the continuum slope around 1000 Angstroms. The continuum longward of 1000 Angstroms can be modeled as a power law f_nu ~ nu (alpha ) with alpha ~ -1. The power--law index between 350 Angstroms and 1000 Angstroms is alpha ~ -2. The break in the power--law index is a feature expected in Comptonized accretion--disk spectra. Electron scattering in a corona above the disk produces a power--law tail in the wavelength band shortward of ~ 1000 Angstroms. Comptonization also smears out the Lyman--limit edge of the intrinsic accretion disk spectrum.

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