The multiple coherence scales of C IV at cosmic noon

The spatial and kinematic structure of the circumgalactic medium remains poorly constrained observationally. We computed the clustering of C IV absorption systems at cosmic noon using quasar pairs. We analyzed VLT/UVES and Keck/HIRES high-resolution spectra ( R ≈ 45 000) of a sample of eight projected and four lensed quasar pairs that probe transverse separations, Δ r , from subkiloparsec to a few megaparsec over the redshift range 1.6 ≲ z ≲ 3.3. We detected and fit Voigt profiles to a total of 141 C IV systems, corresponding to 620 velocity components at all quasar lines of sight. We computed the two-point correlation function of C IV , ξ (Δ v , Δ r ), where Δ v is the velocity difference between components at all available scales. We found a strong dependence of ξ (Δ r ) on Δ r at all velocities. ξ (Δ r ) reaches a sharp peak at the smallest scales we analyzed, Δ r ≈ 0.1 kpc, decreases steadily up to Δ r ≈ 5 kpc, and remains flat up to Δ r ≈ 500 kpc, where it again begins to decrease. By fitting power laws to the projected transverse correlation function Ξ(Δ r ), we inferred two coherence lengths. The first is r 1 = 654 +100 −87 kpc, which we interpret as a representative size for the C IV enriched regions at z ≈ 2, and the second is r 2 = 4.70 +1.60 −1.19 kpc for the individual C IV -bearing clouds. When we instead projected this in Δ r , we found amplitudes of ξ (Δ v ) that were consistent with those in previous works that used quasars and extended background sources. Our results suggest that C IV might be a good tracer of not only the small internal structure of the circumgalactic medium, but also of the way in which galaxies cluster at cosmic noon.