First comparison of ionization and metallicity in two lines of sight toward HE 1104-1805 AB at z=1.66

Using new Nubble Space Telescope Faint Object Spectrograph, the New Technol ogy Telescope ESO Multi Mode Instrument, and Keck HIRES spectra of the grav itationally lensed double QSO HE 1104-1805 AB (z(em) = 2.31) and assuming U V photoionization by a metagalactic radiation held, we derive physical cond itions (ionization levels, metal abundances, and cloud sizes along the line s of sight) in five C IV + Mg II absorption systems clustered around z = 1. 66 along the two lines of sight. Three of these systems are associated with a damped Ly alpha (DLA) system with log N(N I)= 20.85, which is observed i n the UV spectra of the bright QSO image, A. The other two systems are asso ciated with a Lyman-limit system with log N(H I)= 17.57 seen in the fainter image, B. The Cry and Mg II line profiles in A resemble those in the B spe ctra and span Delta v approximate to 360 km s(-1). The angular separation, theta = 3.195 ", between A and B corresponds to a transverse proper separat ion of S-perpendicular to = 8.3 h(50)(-1) kpc for q(0) = 0.5 and a lens at z = 1. Assuming that the relative metal abundances in these absorption syst ems are the same as those observed in the DLA system, we find that the obse rved N(C IV)/N(Mg II) ratios imply ionization parameters of log Gamma = -2. 95 to - 2.35. Consequently, these clouds should be small (0.5-1.6 kpc with a hydrogen density of n(H) less than or similar to 0.01 cm(-3)) and relativ ely highly ionized. The absorption systems to B are found to have a metalli city 0.63 times lower than the metallicity of the gas giving rise to the DL A system, Z(DLA) similar or equal to 1/10 Z(circle dot). We detect O vr at z = 1.66253 in both QSO spectra but no associated N v. Our model calculatio ns lead us to conclude that the C Iv clouds should be surrounded by large ( similar to 100 kpc), highly ionized low-density clouds (n(H) similar to 10( -4) cm(-3)) in which O vr, but only weak C IV, absorption occurs. In this s tate, log Gamma greater than or equal to -1.2 reproduces the observed ratio of N(O vr)/N(N v)> 60. These results are discussed in view of the disk/hal o and hierarchical structure formation models.