2025MNRAS.544.1085B

Gravitational lensing has transformed the field of gas tomography in the intergalactic medium (IGM) and circumgalactic medium (CGM). Here, we use the brightest lensed galaxy identified to date, the Sunburst Arc (z $\approx$ 2.37), to constrain the physical size of foreground absorbers at z $\approx$ 2 in 2D. This galaxy is a confirmed Lyman continuum leaker, where its single leaking region is imaged 12 times over four separate arcs. The separations between the arcs allows for large-scale tomography, while the distances between the images along an arc allow for small-scale tomography. Using Hubble Space Telescope/Wide Field Camera 3 UV/Visible (UVIS) G280 grism observations, we extracted the spectra of the leaking region and fit for absorbers detected along these lines of sight using a binary population and spectral synthesis (BPASS) model for the galaxy. We identified two partial Lyman limit systems (pLLSs) and one Lyman limit system (LLS) across the different spectra and measured their physical sizes. We find consistent H I column densities across $\lesssim$2 kpc and an average H I mass of $\approx 10^3$ ${\rm M}_\odot$ for the absorbers. Given the strong C IV lines associated with two of the absorbers, they are likely located within the CGM of foreground galaxies. The third absorber has no associated metal lines, so it is most likely within the IGM. This study provides the first tomography measurements of pLLSs/LLSs in the CGM and IGM at z $\approx$ 2.