Modeling the cool gas clumps in the circumgalactic medium

A major challenge in CGM studies is determining the three-dimensional (3D) properties from the observed projected observations. Here, we decompose the 3D gas density and spatial distribution of cool clouds by fitting a cool CGM model with the absorption observations, including the cool gas density, Lyα, and Mg II equivalent widths. The clumpiness in the cool CGM is considered by modeling individual clouds. This model has four major components: the radial profile of the cool gas density; the number density of clouds; the absorption properties within individual clouds; and the velocity dispersion in the CGM. The observed cool gas density exhibits a large dispersion of ≈2-3 dex within the virial radius (rᵥᵢᵣ). This dispersion can be reproduced with a combination of the projection effect (i.e., distant low-density clouds projected at small radii) and the intrinsic variation in the gas density. By modeling the probability density functions of gas density at different radii, the cool gas density is modeled as a β-model with a characteristic gas density of log nH,0/ cm⁻³=-2.57-0.25+0.43 at rᵥᵢᵣ and a slope of βc=0.63-0.20+0.16, and the intrinsic dispersion is σ_nH≈ 0.56-0.20+0.19 dex. Assuming a cloud mass of 10⁴M_, we further constrain the number density of cool clouds by jointly reproducing Lyα and Mg II equivalent width samples, resulting into a number density of log n_Ncl,0/ rᵥᵢᵣ⁻³=4.76+0.27-0.21 at rᵥᵢᵣ and a slope of βN=0.65+0.06-0.07. This spatial distribution of the cool CGM leads to a total cool gas mass of log Mcool/M₌10.01+0.06-0.06 for L^* galaxies, while varying the cloud mass from 10³M_ to 10⁶M_ leads to the total cool CGM mass of 9.62-0.07+0.05 to 10.46-0.05+0.05.