Probing coherence in metal absorption towards multiple images of strong gravitationally lensed quasars

We present a tomographic analysis of metal absorption lines arising from the circumgalactic medium (CGM) of galaxies at z ≈ 0.5–2, using Multi Unit Spectroscopic Explorer (MUSE) observations of two background quasars at z ≈ 2.2 and 2.8, which are two of the few currently known quasars with multiple images due to strong gravitational lensing by galaxy clusters at z ≈ 0.6 and 0.5, respectively. The angular separations between different pairs of quasar multiple images enable us to probe the absorption over transverse physical separations of ≈0.4–150 kpc, which are based on strong lensing models exploiting MUSE observations. The fractional difference in rest-frame equivalent width (ΔW_r) of Mg II, Fe II, and C IV absorption increases on average with physical separation, indicating that the metal-enriched gaseous structures become less coherent with distance, with a likely coherence length-scale of ≈10 kpc. However, ΔW_r for all the ions vary considerably over ≈0.08–0.9, indicating a clumpy CGM over the full range of length-scales probed. At the same time, paired Mg II absorption is detected across ≈100–150 kpc at similar line-of-sight velocities, which could be probing cool gas clouds within the same halo. No significant dependence of ΔW_r is found on the equivalent width and redshift of the absorbing gas and on the galaxy environment associated with the absorption. The high-ionization gas phase traced by C IV shows a higher degree of coherence than the low-ionization gas phase traced by Mg II, with ≈90 per cent of C IV systems exhibiting ΔW_r ≤ 0.5 at separations ≤10 kpc compared to ≈50 per cent of Mg II systems.