High-Resolution Spectroscopy of the Bright Quasar HS 1700+6416

Abstract

We have analyzed high-resolution (b ∼ 15 km s<SUP>-1</SUP>) optical spectra of the QSO HS 1700+6416 (ζ<SUB>em</SUB> = 2.72). The high signal-to-noise ratio all across the Lyman alpha forest down to Lyβ at ζ = ζ<SUB>em</SUB> allows a reasonable determination of the neutral hydrogen column density as well as of the velocity dispersion of the intervening clouds. A weak, but significant, trend for stronger lines to be broader suggests that their column densities (N<SUB>HI</SUB>) and Doppler parameters (b) are related. A simplified model of very flattened, highly ionized clouds, gravitationally confined by dark matter, gives a good representation of the data, where the observed N<SUB>HI</SUB>-b correlation is due to orientation effects.