Temperature and Kinematics of C [CSC]iv[/CSC] Absorption Systems

We use Keck HIRES spectra of three intermediate-redshift QSOs to study the physical state and kinematics of the individual components of C IV-selected heavy-element absorption systems. Fewer than 8% of all C IV lines with column densities greater than 10 12.5 cm -2 have Doppler parameters b < 6 km s -1 . A formal decomposition into thermal and nonthermal motion using the simultaneous presence of Si IV gives a mean thermal Doppler parameter b therm (C IV) = 7.2 km s -1 , corresponding to a temperature of 3.8 × 10 4 K, although temperatures possibly in excess of 3 × 10 5 K occur occasionally. We also find tentative evidence for a mild increase of temperature with H I column density. Nonthermal motions within components are typically small (<10 km s -1 ) for most systems, indicative of a quiescent environment. The two-point correlation function (TPCF) of C IV systems on scales up to 500 km s -1 suggests that there is more than one source of velocity dispersion. The shape of the TPCF can be understood if the C IV systems are caused by ensembles of objects with the kinematics of dwarf galaxies on a small scale, while following the Hubble flow on a larger scale. Individual high-redshift C IV components may be the building blocks of future normal galaxies in a hierarchical structure formation scenario.