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Through photoionization modeling, constraints on the physical conditions ofthree z ~ 1.7 single-cloud weak Mg II systems (W_r(2796) < 0.3A) are derived.Constraints are provided by high resolution R = 45,000, high signal-to-noisespectra of the three quasars HE0141-3932, HE0429-4091, and HE2243-6031 which wehave obtained from the ESO archive of VLT/UVES. Results are as follows:  (1) The single-cloud weak Mg II absorption in the three z ~ 1.7 systems isproduced by clouds with ionization parameters of -3.8 < logU < -2.0 and sizesof 1-100 pc.  (2) In addition to the low-ionization phase Mg II clouds, all systems need anadditional 1-3 high-ionization phase C IV clouds within 100 km/s of the Mg IIcomponent. The ionization parameters of the C IV phases range from -1.9 < logU< -1.0, with sizes of tens of parsecs to kiloparsecs.  (3) Two of the three single-cloud weak Mg II absorbers have near-solar orsuper-solar metallicities, if we assume a solar abundance pattern. Althoughsuch large metallicities have been found for z < 1 weak Mg II absorbers, theseare the first high metallicities derived for such systems at higher redshifts.  (4) Two of the three weak Mg II systems also need additional low-metallicity,broad Lya absorption lines, offset in velocity from the metal-line absorption,in order to reproduce the full Lya profile.  (5) Metallicity in single-cloud weak Mg II systems are more than an order ofmagnitude larger than those in Damped Lya systems at z ~ 1.7. In fact, thereappears to be a gradual decrease in metallicity with increasing N(HI), fromthese, the most metal-rich Lya forest clouds, to Lyman limit systems, tosub-DLAs, and finally to the DLAs.

Super-Solar Metallicity in Weak Mg II Absorption Systems at z ~ 1.7