An analysis of \simeq 19 500 narrow ( \la 200 { km s } ^ { -1 } ) C iv \lambda \lambda 1548.2,1550.8 absorbers in \simeq 34 000 Sloan Digital Sky Survey quasar spectra is presented .
The statistics of the number of absorbers as a function of outflow-velocity shows that in approximately two-thirds of outflows , with multiple C iv absorbers present , absorbers are line-locked at the 500 { km s } ^ { -1 } velocity separation of the C iv absorber doublet ; appearing as ‘ triplets ’ in the quasar spectra .
Line-locking is an observational signature of radiative line driving in outflowing material , where the successive shielding of ‘ clouds ’ of material in the outflow locks the clouds together in outflow velocity .
Line-locked absorbers are seen in both broad absorption line quasars ( BALs ) and non-BAL quasars with comparable frequencies and with velocities out to at least 20 000 { km s } ^ { -1 } .
There are no detectable differences in the absorber properties and the dust content of single C iv doublets and line-locked C iv doublets .
The gas associated with both single and line-locked C iv absorption systems includes material with a wide range of ionization potential ( 14-138 eV ) .
Both single and line-locked C iv absorber systems show strong systematic trends in their ionization as a function of outflow velocity , with ionization decreasing rapidly with increasing outflow velocity .
Initial simulations , employing Cloudy , demonstrate that a rich spectrum of line-locked signals at various velocities may be expected due to significant opacities from resonance lines of Li- , He- and H-like ions of O , C and N , along with contributions from He ii and H i resonance lines .
The simulations confirm that line driving can be the dominant acceleration mechanism for clouds with N ( H i ) \simeq 10 ^ { 19 } { cm } ^ { -2 } .