Small‐Scale Structure at High Redshift. II. Physical Properties of the CivAbsorbing Clouds

Keck HIRES spectra were obtained of the separate images of threegravitationally lensed QSOs (UM 673, Q1104-1804, and Q1422+2309). We studiedthe velocity and column density differences in CIV doublets in each QSO. Unlikethe low ionization gas clouds typical of the interstellar gas in the Galaxy ordamped Ly alpha galaxies, the spatial density distribution of CIV absorbing gasclouds turns out to be mostly featureless on scales up to a few hundredparsecs, with column density differences rising to 50 percent or more overseparations beyond a few kpc. Similarly, velocity shear becomes detectable onlyover distances larger than a few hundred pc, rising to 70 km/s at a few kpc.The energy transmitted to the gas is substantially less than in present daystar-forming regions, and the gas is less turbulent on a given spatial scalethan, e.g., local HII regions. The quiescence of CIV clouds, taken with theirprobable low density, imply that these objects are not internal to galaxies.The CIV absorbers could be gas expelled recently to large radii and rainingback onto its parent galaxy, or pre-enriched gas from an earlier (populationIII) episode of star formation, falling into the nearest mass concentration.However, while the metals in the gas may have been formed at higher redshifts,the residual turbulence in the clouds and the minimum coherence length measuredhere imply that the gas was stirred more recently, possibly by star formationevents recurring on a timescale on the order of 10-100 Million years (abstractabbreviated).Comment: latex file plus 15 postscript figures (45 pages in total); to be published in the ApJ, June 20, 2001 issu