We report on the statistics of strong ( W _ { r } > 0.15 Å ) C iv absorbers at z = 1.5 - 3.5 toward high-redshift gamma-ray bursts ( GRBs ) .
In contrast with a recent survey for strong Mg ii absorption systems at z < 2 , we find that the number of C iv absorbers per unit redshift dN / dz does not show a significant deviation from previous surveys using quasi-stellar objects ( QSOs ) as background sources .
We find that the number density of C iv toward GRBs is dN / dz| _ { GRB } ( z \sim 1.5 ) = 2.2 _ { -1.4 } ^ { +2.8 } , dN / dz| _ { GRB } ( z \sim 2.5 ) = 2.3 _ { -1.1 } ^ { +1.8 } and dN / dz| _ { GRB } ( z \sim 3.5 ) = 1.1 _ { -0.9 } ^ { +2.6 } .
These numbers are consistent with previous C iv surveys using QSO spectra .
Binning the entire dataset , we set a 95 \% c.l .
upper limit to the excess of C iv absorbers along GRB sightlines at twice the incidence observed along QSO sightlines .
Furthermore , the distribution of equivalent widths of the GRB and QSO samples are consistent with being drawn from the same parent population .
Although the results for Mg ii and C iv absorbers along GRB sightlines appear to contradict one another , we note that the surveys are nearly disjoint : the C iv survey corresponds to higher redshift and more highly ionized gas than the Mg ii survey .
Nevertheless , analysis on larger statistical samples may constrain properties of the galaxies hosting these metals ( e.g .
mass , dust content ) and/or the coherence-length of the gas giving rise to the metal-line absorption .