An ultraviolet spectrum of the high redshift quasar Q2204–408

Abstract

AN ultraviolet spectrum of the radio-quiet quasar Q2204–408, redshift z = 3.18 (ref. 1), detected with the International Ultraviolet Explorer (IUE) is reported here. The object was selected for observation because of its high Lyman-α flux and the absence of a cut-off at the Lyman limit. The spectrum was obtained on 9 August 1978 with the short wavelength spectrograph which covers the range 1,150–1,950 Å (ref. 2). A finder field for Q2204–408 has been given by Osmer and Smith¹ and as the quasar is too faint (m_v = 17.5) to be detected by the fine error sensor of IUE, a blind off-set technique was used to image the quasar in the large (10 × 20 arc s) aperture of the short wavelength spectrograph. A very faint continuous spectrum of average signal ∼5 DN above a background of ∼60 DN was detected after an exposure of 350 min. (DN stands for data number and 256 DN gives full scale.) An emission feature is also probably present at 1,270 Å (304 Å in the rest frame of the source).