Small‐Scale Structure at High Redshift. III. The Clumpiness of the Intergalactic Medium on Subkiloparsec Scales

Abstract

Spectra obtained with the Keck HIRES instrument of the Lya forests in the lines of sight to the A and C components of the gravitationally lensed quasi-stellar object Q1422]231 were used to investigate the structure of the intergalactic medium at mean redshift SzT D 3.3 on subkiloparsec scales. We measured the cross-correlation amplitude between the two Lya forests for a mean transverse separation of 120 h 50 ~1 pc and computed the rms column density and velocity di †erences between individual absorption systems seen in both lines of sight. The rms di †erences between the velocity centroids of the Lya forest lines were found to be less than about 400 ms~1 for unsaturated H I absorption lines with column densities in the range 12 \ log N(H I) \ 14.13. The rate of energy transfer into the low-density intergalactic medium on a typical scale of 100 pc seems to be lower by 3È4 orders of magnitude than the rate measured earlier for strong C IV metal absorption systems. The tight correlation between H I column density and bary-onic density in the intergalactic medium was used to obtain a conservative upper limit on the rms Ñuc-tuations of the baryonic density Ðeld at SzT \ 3.26, namely, [S(* log o)2T]1@2 ¹ 3.1 ] 10~2 on a scale of 110 pc. The fraction of the absorption lines that are di †erent across the lines of sight was used to h 50 ~1 determine the Ðlling factor of the universe for gas that has su †ered recent hydrodynamic disturbances. We thereby derived upper limits on the Ðlling factor of galactic outÑows at high redshift. Short-lived, short-range ancient winds are essentially unconstrained by this method, but strong winds blowing for a substantial fraction of a Hubble time (at z \ 3.3) appear to Ðll less than 20% of the volume of the universe.