2024ApJ...968....8Q

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 VIλλ 1031, 1037 doublet absorption within a line-of-sight velocity interval of ±250 km s^–1, while the rest show no trace of O VI to a detection limit of $\mathrm{log}{N}_{\mathrm{OVI}}/{\mathrm{cm}}^{-2}\approx 13.7$. Meanwhile, only five galaxies or galaxy groups exhibit the Ne VIIIλλ 770, 780 doublet absorption, down to a limiting column density of $\mathrm{log}{N}_{\mathrm{NeVIII}}/{\mathrm{cm}}^{-2}\approx 14.0$. These O VI- and Ne VIII-bearing halos reside in different galaxy environments with stellar masses ranging from $\mathrm{log}{M}_{\mathrm{star}}/{M}_{\odot }\approx 8$ 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 $\mathrm{log}{M}_{\mathrm{star}}/{M}_{\odot }\approx 9\mbox{--}11$ 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_υ > 40 km s^–1 for galaxies of $\mathrm{log}{M}_{\mathrm{star}}/{M}_{\odot }\gt 9$ 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 $\mathrm{log}{M}_{\mathrm{star}}/{M}_{\odot }\approx 9\mbox{--}10$ based on their high ionization fractions in the CGM.