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Session 5 - High Luminosity AGN.
Display session, Monday, June 10
The flux of a quasar shortward of the rest-frame wavelength of He\sc ii Ly \alpha (304Åshould be depressed due to absorption by He^+ ions in the diffuse intergalactic medium (the Gunn-Peterson effect) and/or absorption by He^+ ions residing in clumps or clouds that make up the Ly \alpha forest. Such absorption was recently detected in a FOC spectrum of the z=3.286 quasar, Q0302-003, by Jakobsen et al. (Nature 370, 35, 1994), but the spectral resolution of the FOC was not sufficient to show whether the absorption is produced by a uniformly distributed medium or by a forest of Ly \alpha lines. Last year, Songaila, Hu amp; Cowie (Nature 375, 124, 1995) used the HIRES echelle spectrograph on Keck to obtain a high-quality spectrum of the H \sc i Ly\alpha forest of Q0302-003. They detected a multitude of Ly\alpha- forest clouds, some with column densities as low as 2\cdot 10^12 cm^-2. They argued that absorption in these clouds is sufficient to account for the observed absorption.
This quasar has now been observed by the Goddard High Resolution Spectrograph (GHRS) at 0.6 Å\ resolution, and it is a planned target of observation by the Space Telescope Imaging Spectrograph (STIS), an instrument scheduled to be installed on HST in February 1997. In this paper, we describe the findings from the GHRS observations and evaluate the prospects for future STIS observations.
Program listing for Monday