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Abstract 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 Oviand Neviiiabsorption. The galaxies and associated neighbors are identified at <1 physical Mpc from the sightlines toward 15 CUBS QSOs atz_QSO≳ 0.8. A total of 30 galaxies or galaxy groups exhibit associated Oviλλ1031, 1037 doublet absorption within a line-of-sight velocity interval of ±250 km s⁻¹, while the rest show no trace of Ovito a detection limit of $\log N_{\mathrm{OVI}}/{\mathrm{cm}}^{-2}\approx 13.7$. Meanwhile, only five galaxies or galaxy groups exhibit the Neviiiλλ770, 780 doublet absorption, down to a limiting column density of $\log N_{\mathrm{NeVIII}}/{\mathrm{cm}}^{-2}\approx 14.0$. These Ovi- and Neviii-bearing halos reside in different galaxy environments with stellar masses ranging from $\log M_{\mathrm{star}}/M_{\odot }\approx 8$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 $\log M_{\mathrm{star}}/M_{\odot }\approx 9–11$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 Oviabsorption is broad withσ_υ> 40 km s⁻¹for 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 Oviand Neviiiis suggested to be the dominant phase in sub-L* galaxies with $\log M_{\mathrm{star}}/M_{\odot }\approx 9–10$based on their high ionization fractions in the CGM. 

Abstract We present an analysis of 10 ks snapshot Chandra observations of 12 shocked post-starburst galaxies, which provide a window into the unresolved question of active galactic nuclei (AGN) activity in post-starburst galaxies and its role in the transition of galaxies from active star formation to quiescence. While seven of the 12 galaxies have statistically significant detections (with two more marginal detections), the brightest only obtained 10 photons. Given the wide variety of hardness ratios in this sample, we chose to pursue a forward-modeling approach to constrain the intrinsic luminosity and obscuration of these galaxies, rather than stacking. We constrain the intrinsic luminosity of obscured power laws based on the total number of counts and spectral shape, itself mostly set by the obscuration, with hardness ratios consistent with the data. We also tested thermal models. While all the galaxies have power-law models consistent with their observations, a third of the galaxies are better fit as an obscured power law and another third are better fit as thermal emission. If these post-starburst galaxies, early in their transition, contain AGNs, then these are mostly confined to lower obscuration ( N H ≤ 10 23 cm −2 ) and lower luminosity ( L 2−10 keV ≤ 10 42 erg s −1 ). Two galaxies, however, are clearly best fit as significantly obscured AGNs. At least half of this sample shows evidence of at least low-luminosity AGN activity, though none could radiatively drive out the remaining molecular gas reservoirs. Therefore, these AGNs are more likely along for the ride, having been fed gas by the same processes driving the transition. 

ABSTRACT We present a detailed study of two partial Lyman limit systems (pLLSs) of neutral hydrogen column density $$N_\mathrm{H\, I}\approx (1-3)\times 10^{16}\, \mathrm{cm}^{-2}$$ discovered at $$z$$ = 0.5 in the Cosmic Ultraviolet Baryon Survey (CUBS). Available far-ultraviolet spectra from the Hubble Space Telescope Cosmic Origins Spectrograph and optical echelle spectra from MIKE on the Magellan Telescopes enable a comprehensive ionization analysis of diffuse circumgalactic gas based on resolved kinematics and abundance ratios of atomic species spanning five different ionization stages. These data provide unambiguous evidence of kinematically aligned multiphase gas that masquerades as a single-phase structure and can only be resolved by simultaneous accounting of the full range of observed ionic species. Both systems are resolved into multiple components with inferred α-element abundance varying from [α/H] ≈−0.8 to near solar and densities spanning over two decades from log nH/cm−3 ≈ −2.2 to <−4.3. Available deep galaxy survey data from the CUBS program taken with VLT/MUSE, Magellan/LDSS3-C and Magellan/IMACS reveal that the $$z$$ = 0.47 system is located 55 kpc from a star-forming galaxy with prominent Balmer absorption of stellar mass $${{M_{\rm star}}}\approx 2\times 10^{10}\, {{M_{\odot}}}$$, while the $$z$$ = 0.54 system resides in an overdense environment of 11 galaxies within 750 kpc in projected distance, with the most massive being a luminous red galaxy of $${{M_{\rm star}}}\approx 2\times 10^{11}\, {{M_{\odot}}}$$ at 375 kpc. The study of these two pLLSs adds to an emerging picture of the complex, multiphase circumgalactic gas that varies in chemical abundances and density on small spatial scales in diverse galaxy environments. The inhomogeneous nature of metal enrichment and density revealed in observations must be taken into account in theoretical models of diffuse halo gas. 

ABSTRACT We constrain the evolution of the brightest cluster galaxy plus intracluster light (BCG + ICL) using an ensemble of 42 galaxy groups and clusters that span redshifts of z = 0.05−1.75 and masses of M500,c= 2 × 1013−1015 M⊙. Specifically, we measure the relationship between the BCG + ICL stellar mass M⋆ and M500,c at projected radii 10 < r < 100 kpc for three different epochs. At intermediate redshift ($$\bar{z}=0.40$$), where we have the best data, we find M⋆ ∝ M500,c0.48 ± 0.06. Fixing the exponent of this power law for all redshifts, we constrain the normalization of this relation to be 2.08 ± 0.21 times higher at $$\bar{z}=0.40$$ than at high redshift ($$\bar{z}=1.55$$). We find no change in the relation from intermediate to low redshift ($$\bar{z}=0.10$$). In other words, for fixed M500,c, M⋆ at 10 < r < 100 kpc increases from $$\bar{z}=1.55$$ to $$\bar{z}=0.40$$ and not significantly thereafter. Theoretical models predict that the physical mass growth of the cluster from z = 1.5 to z = 0 within r500,c is 1.4×, excluding evolution due to definition of r500,c. We find that M⋆ within the central 100 kpc increases by ∼3.8× over the same period. Thus, the growth of M⋆ in this central region is more than a factor of 2 greater than the physical mass growth of the cluster as a whole. Furthermore, the concentration of the BCG + ICL stellar mass, defined by the ratio of stellar mass within 10 kpc to the total stellar mass within 100 kpc, decreases with increasing M500,c at all z. We interpret this result as evidence for inside–out growth of the BCG + ICL over the past 10 Gyr, with stellar mass assembly occurring at larger radii at later times. 

ABSTRACT We present a systematic investigation of physical conditions and elemental abundances in four optically thick Lyman-limit systems (LLSs) at z = 0.36–0.6 discovered within the cosmic ultraviolet baryon survey (CUBS). Because intervening LLSs at z < 1 suppress far-UV (ultraviolet) light from background QSOs, an unbiased search of these absorbers requires a near-UV-selected QSO sample, as achieved by CUBS. CUBS LLSs exhibit multicomponent kinematic structure and a complex mix of multiphase gas, with associated metal transitions from multiple ionization states such as C ii, C iii, N iii, Mg ii, Si ii, Si iii, O ii, O iii, O vi, and Fe ii absorption that span several hundred km s−1 in line-of-sight velocity. Specifically, higher column density components (log N(H i)/cm−2≳ 16) in all four absorbers comprise dynamically cool gas with $$\langle T \rangle =(2\pm 1) \times 10^4\,$$K and modest non-thermal broadening of $$\langle b_\mathrm{nt} \rangle =5\pm 3\,$$km s−1. The high quality of the QSO absorption spectra allows us to infer the physical conditions of the gas, using a detailed ionization modelling that takes into account the resolved component structures of H i and metal transitions. The range of inferred gas densities indicates that these absorbers consist of spatially compact clouds with a median line-of-sight thickness of $$160^{+140}_{-50}$$ pc. While obtaining robust metallicity constraints for the low density, highly ionized phase remains challenging due to the uncertain $$N\mathrm{(H\, {\small I})}$$, we demonstrate that the cool-phase gas in LLSs has a median metallicity of $$\mathrm{[\alpha /H]_{1/2}}=-0.7^{+0.1}_{-0.2}$$, with a 16–84 percentile range of [α/H] = (−1.3, −0.1). Furthermore, the wide range of inferred elemental abundance ratios ([C/α], [N/α], and [Fe/α]) indicate a diversity of chemical enrichment histories. Combining the absorption data with deep galaxy survey data characterizing the galaxy environment of these absorbers, we discuss the physical connection between star-forming regions in galaxies and diffuse gas associated with optically thick absorption systems in the z < 1 circumgalactic medium.