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

Abstract

This paper presents a newly established sample of 103 unique galaxies or galaxy groups at $0.4\lesssim z\lesssim 0.7$ 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 $z_{\mathrm{QSO}}\gtrsim 0.8$. A total of 30 galaxies or galaxy groups exhibit associated O VI $\lambda \lambda$ 1031, 1037 doublet absorption within a line-of-sight velocity interval of $\pm 250$ km/s, while the rest show no trace of O VI to a detection limit of $\log N_{\mathrm{OVI}}/\mathrm{c}{\mathrm{m}}^{-2}\approx 13.7$. Meanwhile, only five galaxies or galaxy groups exhibit the Ne VIII $\lambda \lambda$ 770,780 doublet absorption, down to a limiting column density of $\log N_{\mathrm{NeVIII}}/\mathrm{c}{\mathrm{m}}^{-2}\approx 14.0$. These O VI- and Ne VIII-bearing halos reside in different galaxy environments with stellar masses ranging from $\log M_{\mathrm{star}}/M_{\odot }\approx 8$ to $\approx 11.5$. 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 $\log M_{\mathrm{star}}/M_{\odot }\approx 9-11$ 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 ${\sigma }_v>40$ km/s for galaxies of $\log M_{\mathrm{star}}/M_{\odot }>9$ 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-$L^{\ast }$ galaxies with $\log M_{\mathrm{star}}/M_{\odot }\approx 9-10$ based on their high ionization fractions in the CGM.

Submitted to ApJ after addressing the referee's comments; 28 pages, 16 figures