Search

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 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.

Turbulent motions in the circumgalactic medium play a critical role in regulating the evolution of galaxies, yet their detailed characterization remains elusive. Using two-dimensional velocity maps constructed from spatially extended [O ii ] and [O iii ] emission, Chen et al. measured the velocity structure functions (VSFs) of four quasar nebulae at z ≈ 0.5–1.1. One of these exhibits a spectacular Kolmogorov relation. Here, we carry out an ensemble study using an expanded sample incorporating four new nebulae from three additional quasi-stellar object (QSO) fields. The VSFs measured for all eight nebulae are best explained by subsonic turbulence revealed by the line-emitting gas, which in turn strongly suggests that the cool gas ( T ∼ 10 ^4 K) is dynamically coupled to the hot ambient medium. Previous work demonstrates that the largest nebulae in our sample reside in group environments with clear signs of tidal interactions, suggesting that environmental effects are vital in seeding and enhancing the turbulence within the gaseous halos, ultimately promoting the formation of the extended nebulae. No discernible differences are observed in the VSF properties between radio-loud and radio-quiet QSO fields. We estimate the turbulent heating rate per unit volume, Q _turb , in the QSO nebulae to be ∼10 ^−26 –10 ^−22 erg cm ^−3 s ^−1 for the cool phase and ∼10 ^−28 –10 ^−25 erg cm ^−3 s ^−1 for the hot phase. This range aligns with measurements in the intracluster medium and star-forming molecular clouds but is ∼10 ^3 times higher than the Q _turb observed inside cool gas clumps on scales ≲1 kpc using absorption-line techniques. We discuss the prospect of bridging the gap between emission and absorption studies by pushing the emission-based VSF measurements to below ≈10 kpc.

This paper presents a newly established sample of 19 unique galaxies and galaxy groups at redshift z  = 0.89–1.21 in six QSO fields from the Cosmic Ultraviolet Baryon Survey (CUBS), designated as the CUBSz1 sample. In this sample, nine galaxies or galaxy groups show absorption features, while the other 10 systems exhibit 2σ upper limits of |$\log N (\rm{He\,{\small I}})/\mbox{${\rm cm^{-2}}$}\lesssim 13.5$| and |$\log N (\rm{O\,{\small V}})/\mbox{${\rm cm^{-2}}$}\lesssim 13.3$|⁠. Environmental properties of the galaxies, including galaxy overdensities, the total stellar mass and gravitational potential summed over all neighbours, and the presence of local ionizing sources, are found to have a significant impact on the observed CGM absorption properties. Specifically, massive galaxies and galaxies in overdense regions exhibit a higher rate of incidence of absorption. The CGM absorption properties in galaxy groups appear to be driven by the galaxy closest to the QSO sightline, rather than by the most massive galaxy or by mass-weighted properties. We introduce a total projected gravitational potential ψ, defined as −ψ/ G  = ∑ M halo/ d proj summed over all group members, to characterize the galaxy environment. This projected gravitational potential correlates linearly with the maximum density detected in each sightline (i.e. a power-law slope of |$0.95_{-0.14}^{+0.15}$|⁠), consistent with higher pressure gas being confined in deeper gravitational potential wells. In addition, we find that the radial profile of cool gas density exhibits a decline from the inner regions to the outskirts, and the amplitude is consistent with the cool gas being in pressure balance with the hot halo. Finally, we note that the ionizing flux from nearby galaxies can elevate the N (H  i)/ N (He  i) ratio, which provides a unique diagnostic of possible local sources contributing to the ionizing radiation field. [ABSTRACT FROM AUTHOR]

We present the first empirical constraints on the turbulent velocity field of the diffuse circumgalactic medium around four luminous quasi-stellar objects (QSOs) at z ≈ 0.5–1.1. Spatially extended nebulae of ≈50–100 physical kpc in diameter centred on the QSOs are revealed in [O  ii ]  |$\lambda \lambda \, 3727,3729$| and/or [O  iii ]  |$\lambda \, 5008$| emission lines in integral field spectroscopic observations obtained using Multi-Unit Spectroscopic Explorer on the Very Large Telescope. We measure the second- and third-order velocity structure functions (VSFs) over a range of scales, from ≲5 kpc to ≈20–50 kpc, to quantify the turbulent energy transfer between different scales in these nebulae. While no constraints on the energy injection and dissipation scales can be obtained from the current data, we show that robust constraints on the power-law slope of the VSFs can be determined after accounting for the effects of atmospheric seeing, spatial smoothing, and large-scale bulk flows. Out of the four QSO nebulae studied, one exhibits VSFs in spectacular agreement with the Kolmogorov law, expected for isotropic, homogeneous, and incompressible turbulent flows. The other three fields exhibit a shallower decline in the VSFs from large to small scales. However, with a limited dynamic range in the spatial scales in seeing-limited data, no constraints can be obtained for the VSF slopes of these three nebulae. For the QSO nebula consistent with the Kolmogorov law, we determine a turbulence energy cascade rate of ≈0.2 cm2 s−3. We discuss the implication of the observed VSFs in the context of QSO feeding and feedback in the circumgalactic medium. [ABSTRACT FROM AUTHOR]

This paper presents a systematic study of the photoionization and thermodynamic properties of the cool circumgalactic medium (CGM) as traced by rest-frame ultraviolet absorption lines around 26 galaxies at redshift z ≲ 1. The study utilizes both high-quality far-ultraviolet and optical spectra of background QSOs and deep galaxy redshift surveys to characterize the gas density, temperature, and pressure of individual absorbing components and to resolve their internal non-thermal motions. The derived gas density spans more than three decades, from |$\log (n_{\rm H}/{{\rm cm^{-3}}}) \approx -4$| to −1, while the temperature of the gas is confined in a narrow range of log (T /K) ≈ 4.3 ± 0.3. In addition, a weak anticorrelation between gas density and temperature is observed, consistent with the expectation of the gas being in photoionization equilibrium. Furthermore, decomposing the observed line widths into thermal and non-thermal contributions reveals that more than 30 per cent of the components at z ≲ 1 exhibit line widths driven by non-thermal motions, in comparison to <20 per cent found at z ≈ 2–3. Attributing the observed non-thermal line widths to intra-clump turbulence, we find that massive quenched galaxies on average exhibit higher non-thermal broadening/turbulent energy in their CGM compared to star-forming galaxies at z ≲ 1. Finally, strong absorption features from multiple ions covering a wide range of ionization energy (e.g. from Mg  ii to O  iv) can be present simultaneously in a single absorption system with kinematically aligned component structure, but the inferred pressure in different phases may differ by a factor of ≈10. [ABSTRACT FROM AUTHOR]

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  n H/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 FROM AUTHOR]

This paper presents a survey of Mg  ii absorbing gas in the vicinity of 380 random galaxies, using 156 background quasi-stellar objects (QSOs) as absorption-line probes. The sample comprises 211 isolated (73 quiescent and 138 star-forming galaxies) and 43 non-isolated galaxies with sensitive constraints for both Mg  ii absorption and H α emission. The projected distances span a range from d  = 9 to 497 kpc, redshifts of the galaxies range from z  = 0.10 to 0.48, and rest-frame absolute B -band magnitudes range from M B = −16.7 to −22.8. Our analysis shows that the rest-frame equivalent width of Mg  ii , Wr (2796), depends on halo radius (R h), B -band luminosity(L B), and stellar mass (M star) of the host galaxies, and declines steeply with increasing d for isolated, star-forming galaxies. At the same time, Wr (2796) exhibits no clear trend for either isolated, quiescent galaxies or non-isolated galaxies. In addition, the covering fraction of Mg  ii absorbing gas 〈κ〉 is high with 〈κ〉 ≳ 60 per cent at <40 kpc for isolated galaxies and declines rapidly to 〈κ〉 ≈ 0 at d ≳ 100 kpc. Within the gaseous radius, the incidence of Mg  ii gas depends sensitively on both M star and the specific star formation rate inferred from H α. Different from what is known for massive quiescent haloes, the observed velocity dispersion of Mg  ii absorbing gas around star-forming galaxies is consistent with expectations from virial motion, which constrains individual clump mass to |$m_{\rm cl} \gtrsim 10^5 \, \rm M_\odot$| and cool gas accretion rate of |$\sim 0.7\!-\!2 \, \mathrm{ M}_\odot \, \rm yr^{-1}$|⁠. Finally, we find no strong azimuthal dependence of Mg  ii absorption for either star-forming or quiescent galaxies. Our results demonstrate that multiple parameters affect the properties of gaseous haloes around galaxies and highlight the need of a homogeneous, absorption-blind sample for establishing a holistic description of chemically enriched gas in the circumgalactic space. [ABSTRACT FROM AUTHOR]

We present initial results from the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS is designed to map diffuse baryonic structures at redshift z ≲ 1 using absorption-line spectroscopy of 15 UV-bright QSOs with matching deep galaxy survey data. CUBS QSOs are selected based on their NUV brightness to avoid biases against the presence of intervening Lyman limit systems (LLSs) at z abs < 1. We report five new LLSs of |$\log \, N({\mathrm{ H} \,{\small I}})/{{\rm cm^{-2}}}\gtrsim 17.2$| over a total redshift survey path-length of |$\Delta \, z_{\mathrm{ LL}}=9.3$|⁠ , and a number density of |$n(z)=0.43_{-0.18}^{+0.26}$|⁠. Considering all absorbers with |$\log \, N({{\mathrm{ H} \,{\small I}}})/{{\rm cm^{-2}}}\gt 16.5$| leads to |$n(z)=1.08_{-0.25}^{+0.31}$| at z abs < 1. All LLSs exhibit a multicomponent structure and associated metal transitions from multiple ionization states such as C  ii , C  iii , Mg  ii , Si  ii , Si  iii , and O  vi absorption. Differential chemical enrichment levels as well as ionization states are directly observed across individual components in three LLSs. We present deep galaxy survey data obtained using the VLT-MUSE integral field spectrograph and the Magellan Telescopes, reaching sensitivities necessary for detecting galaxies fainter than |$0.1\, L_*$| at d ≲ 300 physical kpc (pkpc) in all five fields. A diverse range of galaxy properties is seen around these LLSs, from a low-mass dwarf galaxy pair, a co-rotating gaseous halo/disc, a star-forming galaxy, a massive quiescent galaxy, to a galaxy group. The closest galaxies have projected distances ranging from d = 15 to 72 pkpc and intrinsic luminosities from |${\approx} 0.01\, L_*$| to |${\approx} 3\, L_*$|⁠. Our study shows that LLSs originate in a variety of galaxy environments and trace gaseous structures with a broad range of metallicities. [ABSTRACT FROM AUTHOR]

We present a systematic investigation of the circumgalactic medium (CGM) within projected distances d < 160 kpc of luminous red galaxies (LRGs). The sample comprises 16 intermediate-redshift (⁠|$z$|  = 0.21–0.55) LRGs of stellar mass |$M_\mathrm{star}\gt 10^{11}\, \mathrm{M}_\odot$|⁠. Combining far-ultraviolet Cosmic Origin Spectrograph spectra from the Hubble Space Telescope and optical echelle spectra from the ground enables a detailed ionization analysis based on resolved component structures of a suite of absorption transitions, including the full H  i Lyman series and various ionic metal transitions. By comparing the relative abundances of different ions in individually matched components, we show that cool gas (T ∼ 104 K) density and metallicity can vary by more than a factor of 10 in an LRG halo. Specifically, metal-poor absorbing components with <1/10 solar metallicity are seen in 50 per cent of the LRG haloes, while gas with solar and super-solar metallicity is also common. These results indicate a complex multiphase structure and poor chemical mixing in these quiescent haloes. We calculate the total surface mass density of cool gas, Σcool, by applying the estimated ionization fraction corrections to the observed H  i column densities. The radial profile of Σcool is best described by a projected Einasto profile of slope α = 1 and scale radius r s = 48 kpc. We find that typical LRGs at |$z$| ∼ 0.4 contain cool gas mass of |$\mathrm{\mathit {M}_{cool} = (1-2)\times 10^{10}\, \mathrm{M_\odot }}$| at d < 160 kpc (or as much as |$\mathrm{\mathit {M}_{cool} \approx 4\times 10^{10}\, \mathrm{M_\odot }}$| at d < 500 kpc), comparable to the cool CGM mass of star-forming galaxies. Furthermore, we show that high-ionization O  vi and low-ionization absorption species exhibit distinct velocity profiles, highlighting their different physical origins. We discuss the implications of our findings for the origin and fate of cool gas in LRG haloes. [ABSTRACT FROM AUTHOR]