The Cosmic Ultraviolet Baryon Survey (CUBS) VII: on the warm-hot circumgalactic medium probed by O VI and Ne VIII at 0.4 ≲ z ≲ 0.7

This paper presents a newly established sample of 103 unique galaxies or galaxy groups at 0.4≲ z≲ 0.7 from the Cosmic Ultraviolet Baryon Survey (CUBS) for studying the warm-hot circumgalactic medium (CGM) probed by both O VI and Ne VIII absorption. The galaxies and associated neighbors are identified at < 1 physical Mpc from the sightlines toward 15 CUBS QSOs at z_ QSO≳ 0.8. A total of 30 galaxies or galaxy groups exhibit associated O VI λλ 1031, 1037 doublet absorption within a line-of-sight velocity interval of ±250 km/s, while the rest show no trace of O VI to a detection limit of log N_ OVI/ cm^-2≈13.7. Meanwhile, only five galaxies or galaxy groups exhibit the Ne VIII λλ 770,780 doublet absorption, down to a limiting column density of log N_ NeVIII/ cm^-2≈14.0. These O VI- and Ne VIII-bearing halos reside in different galaxy environments with stellar masses ranging from log M_ star/M_⊙≈ 8 to ≈11.5. The warm-hot CGM around galaxies of different stellar masses and star formation rates exhibits different spatial profiles and kinematics. In particular, star-forming galaxies with log M_ star/M_⊙≈9-11 show a significant concentration of metal-enriched warm-hot CGM within the virial radius, while massive quiescent galaxies exhibit flatter radial profiles of both column densities and covering fractions. In addition, the velocity dispersion of O VI absorption is broad with σ_v > 40 km/s for galaxies of log M_ star/M_⊙>9 within the virial radius, suggesting a more dynamic warm-hot halo around these galaxies. Finally, the warm-hot CGM probed by O VI and Ne VIII is suggested to be the dominant phase in sub-L^* galaxies with log M_ star/M_⊙≈9-10 based on their high ionization fractions in the CGM.