Comparison of the X-ray emitting gas mass from the simulation and the gas mass retrieved from single β-profiles using Eqs. (10)–(12). The solid blue diagonal line indicates equality between the two methods. The horizontal purple dashed line indicates $M_{\mathrm{gas}}^{\mathrm{true}}$ for a halo with 1000 gas resolution elements. Galaxies with $M_{\mathrm{gas}}^{\mathrm{true}}\lesssim {10}^{10}{\mathrm{M}}_{\odot }$ have more poorly resolved atmospheres.