Ratio of neutral argon Ar I to Si II column density (relative to solar), [Ar/Si], plotted as a function of the H I column density. Red stars indicate measurements for ESDLAs from this work, with empty stars indicating tentative detections of Ar I and down arrows representing upper limits. Blue squares are measurements for DLAs from Zafar et al. (2014). The green dots represent a series of photoionisation models run by Zafar et al. (2014) for gas with a solar abundance ratio, low density (n_H = 0.1 atoms cm⁻³), and Haardt & Madau (HM) extragalactic background radiation (see Haardt & Madau 2012) at z = 2.5. The purple dots also represent similar models, but with a lower density (n_H = 0.01 atoms cm⁻³). The cyan points are a series of photo-ionisation models from this work with an updated Khaire & Srianand extragalactic background radiation field (see Khaire & Srianand 2019) and the cosmic microwave background (CMB) at redshift, z = 2.5, solar abundance ratios, log N(H I) ranging from 20 to 22.5, a metallicity of [Zn/H]∼0.05 solar (average ESDLA metallicity), and a density, n_H = 0.1 cm⁻³. The photoionisation model results were obtained using CLOUDY.