Transverse clues on the kiloparsec-scale structure of the circumgalactic medium as traced by C IV absorption

¹ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
² Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
³ Dipartimento di Fisica e Astronomia, Università di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy
⁴ Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla, 4059 Valparaíso, Chile
⁵ European Southern Observatory, Alonso de Córdova, 3107 Vitacura, Casilla, 19001 Santiago, Chile
⁶ Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
⁷ NRC Herzberg Astronomy and Astrophysics Research Centre, 5071 West Saanich Road, Victoria, B.C. V9E 2E7, Canada
⁸ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
⁹ Department of Physics, University of Cincinnati, Cincinnati, OH 45221, USA
¹⁰ French-Chilean Laboratory for Astronomy, IRL 3386, CNRS and U. de Chile, Casilla 36-D, Santiago, Chile
¹¹ Centre de Recherche Astrophysique de Lyon, Université de Lyon 1, ENS-Lyon, UMR5574, 9 Av Charles André, 69230 Saint-Genis-Laval, France
¹² Institut d’Astrophysique de Paris, CNRS-SU, UMR 7095, 98bis bd Arago, 75014 Paris, France

^⋆ Corresponding author; slopez@das.uchile.cl

Received: 20 June 2024
Accepted: 3 October 2024

Abstract

The kiloparsec-scale kinematics and density structure of the circumgalactic medium (CGM) is still poorly constrained observationally, which poses a problem for understanding the role of the baryon cycle in galaxy evolution. Here we present VLT/MUSE integral-field spectroscopy (R ≈ 1800) of four giant gravitational arcs exhibiting W₀ ≳ 0.2 Å C IV absorption at eight intervening redshifts, z_abs ≈ 2.0–2.5. We detected C IV absorption in a total of 222 adjacent and seeing-uncorrelated sight lines whose spectra sample beams of (“de-lensed”) linear size ≈1 kpc. Our data show that (1) absorption velocities cluster at all probed transverse scales, Δr_⊥ ≈ 0–15 kpc, depending on system; (2) the (transverse) velocity dispersion never exceeds the mean (line-of-sight) absorption spread; and (3) the (transverse) velocity autocorrelation function does not resolve kinematic patterns at the above spatial scales, but its velocity projection, ξ^arc(Δv), exhibits a similar shape to the known two-point correlation function toward quasars, ξ^QSO(Δv). An empirical kinematic model suggests that these results are a natural consequence of wide-beam observations of an unresolved clumpy medium. Our model recovers both the underlying velocity dispersion of the clumps (70–170 km s⁻¹) and the mean number of clumps per unit area (2–13 kpc⁻²). The latter constrains the projected mean inter-clump distance to within ≈0.3–0.8 kpc, which we argue is a measure of clump size for a near-unity covering fraction. The model is also able to predict ξ^arc(Δv) from ξ^QSO(Δv), suggesting that the strong systems that shape ξ^arc(Δv) and the line-of-sight velocity components that define ξ^QSO(Δv) trace the same kinematic population. Consequently, the clumps must possess an internal density structure that generates both weak and strong components. We discuss how our interpretation is consistent with previous observations using background galaxies and multiple quasars as well as its implications for the connection between the small-scale kinematic structure of the CGM and galactic-scale accretion and feedback processes.