The Absorption Signatures of Dwarf Galaxies: Thez = 1.04 Multicloud Weak MgiiAbsorber toward PG 1634+706

We analyze high resolution spectra of a multi--cloud weak [defined asW_r(MgII) < 0.3 A] absorbing system along the line of sight to PG 1634+706.This system gives rise to a partial Lyman limit break and absorption in MgII,SiII, CII, SiIII, SiIV, CIV, and OVI. The lower ionization transitions arise intwo kinematic subsystems with a separation of ~150 km/s. Each subsystem isresolved into several narrow components, having Doppler widths of 3-10 kms. Forboth subsystems, the OVI absorption arises in a separate higher ionizationphase, in regions dominated by bulk motions in the range of 30-40 km/s. The twoOVI absorption profiles are kinematically offset by ~50 km/s with respect toeach of the two lower ionization subsystem. In the stronger subsystem, theSiIII absorption is strong with a distinctive, smooth profile shape and maypartially arise in shock heated gas. Moreover, the kinematic substructure ofSiIV traces that of the lower ionization MgII, but may be offset by ~3 km/s.Based upon photoionization models, constrained by the partial Lyman limitbreak, we infer a low metallicity of ~0.03 solar for the low ionization gas inboth subsystems. The broader OVI phases have a somewhat higher metallicity, andthey are consistent with photoionization; the profiles are not broad enough toimply production of OVI through collisional ionization. Various models,including outer disks, dwarf galaxies, and superwinds, are discussed to accountfor the phase structure, metallicity, and kinematics of this absorption system.We favor an interpretation in which the two subsystems are produced bycondensed clouds far out in the opposite extremes of a multi-layer dwarf galaxysuperwind