The Cosmic Ultraviolet Baryon Survey X: Density and Pressure Profiles of Clumpy Circumgalactic Gas at $z=0.4-0.7$

The thermodynamic state and turbulent properties of the cool circumgalactic medium (CGM) are investigated for 23 galaxies and galaxy groups at intermediate redshift ($z=0.4$–0.7) in the Cosmic Ultraviolet Baryon Survey (CUBS) midz sample using background QSOs within the virial radius. Kinematically resolved absorption-line measurements from Hubble Space Telescope/COS and STIS spectra, combined with photoionization modeling, yield gas densities of $n_\mathrm{H}\approx10^{-4}$–$10^{-2} \ \mathrm{cm}^{-3}$, temperatures of $T\approx(1$–$5) \times 10^4\,\mathrm{K}$, and non-thermal line broadening of $b_\mathrm{NT}\approx2$–$30 \ \mathrm{km \ s^{-1}}$ for individual cool clumps. Combined with published samples at similar redshifts, the results indicate that photoionization equilibrium accurately describes the cool CGM and that turbulent motions are predominantly subsonic. At fixed projected distance, cool-gas density decreases systematically with halo mass, while inferred cool-gas pressures in $M_h\approx10^{12}$–$10^{13}\,\mathrm{M}_\odot$ halos are consistent with hot-gas pressures inferred from stacked X-ray observations. The analysis uncovers a near constant total cool gas mass across a broad halo mass range, which directly translates to a declining baryon mass fraction in the cool phase from $\approx 6$–$19\%$ in halos of $M_h \approx 10^{12}\, \mathrm{M}_\odot$ to $\approx 0.6$–$1.5\%$ in halos of $M_h \approx 10^{13}\, \mathrm{M}_\odot$. Finally, several CUBS galaxies exhibit kinematically aligned low- and high-ionization species spanning up to two orders of magnitude in density, reflecting local fluctuations in the halo gas pressure.