We present initial results from the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS is designed to map diffuse baryonic structures at redshift z less than or similar to 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(H I)/cm(-2) greater than or similar to 17.2 over a total redshift survey path-length of Delta z(LL) = 9.3, and a number density of n(z) = 0.43(-0.18)(+0.26) . Considering all absorbers with log N(H I)/cm(-2) > 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, CIII, MgII, Si II, Si III, and OVI 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 0.1L(*) at d less than or similar to 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 approximate to 0.01L(*) to approximate to 3L(*). Our study shows that LLSs originate in a variety of galaxy environments and trace gaseous structures with a broad range of metallicities.

We present new measurements of the spatial distribution and kinematics of neutral hydrogen in the circumgalactic and intergalactic medium surrounding star-forming galaxies at z similar to 2. Using the spectra of similar or equal to 3000 galaxies with redshifts < z > = 2.3 +/- 0.4 from the Keck Baryonic Structure Survey, we assemble a sample of more than 200 000 distinct foreground-background pairs with projected angular separations of 3-500 arcsec and spectroscopic redshifts, with < z(fg)> = 2.23 and < z(bg)> = 2.57 (foreground, background redshifts, respectively.) The ensemble of sightlines and foreground galaxies is used to construct a 2D map of the mean excess HI Ly alpha optical depth relative to the intergalactic mean as a function of projected galactocentric distance (20 less than or similar to D-tran/pkpc less than or similar to 4000) and line-of-sight velocity. We obtain accurate galaxy systemic redshifts, providing significant information on the line-of-sight kinematics of HI gas as a function of projected distance D-tran. We compare the map with cosmological zoom-in simulation, finding qualitative agreement between them. A simple two-component (accretion, outflow) analytical model generally reproduces the observed line-of-sight kinematics and projected spatial distribution of HI. The best-fitting model suggests that galaxy-scale outflows with initial velocity v(out) similar or equal to 600 km s(-1) dominate the kinematics of circumgalactic HI out to D-tran similar or equal to 50 kpc, while HI at D-tran greater than or similar to 100 kpc is dominated by infall with characteristic v(in) less than or similar to circular velocity. Over the impact parameter range 80 less than or similar to D-tran/pkpc less than or similar to 200, the HI line-of-sight velocity range reaches a minimum, with a corresponding flattening in the rest-frame Ly alpha equivalent width. These observations can be naturally explained as the transition between outflow-dominated and accretion-dominated flows. Beyond D-tran similar or equal to 300 pkpc (similar to 1 cMpc), the line-of-sight kinematics are dominated by Hubble expansion.

We report the serendipitous detection of an H-2-bearing damped Lya absorber at z = 0.576 in the spectrum of the QSO J0111-0316 in the Cosmic Ultraviolet Baryon Survey. Spectroscopic observations from Hubble Space Telescope-COS in the far-ultraviolet reveal a damped absorber with log[N(H I)/cm(-2)] = 20.1 +/- 0.2 and log[N(H-2)/cm(-2)] = 18.97(-0.06)(+0.05). The diffuse molecular gas is found in two velocity components separated by Delta nu 60 km s(-1), with >99.9% of the total H-2 column density concentrated in one component. At a metallicity of approximate to 50% of solar, there is evidence for Fe enhancement and dust depletion, with a dust-to-gas ratio kappa(O) approximate to 0.4. A galaxy redshift survey conducted with IMACS and LDSS-3C on Magellan reveals an overdensity of nine galaxies at projected distance d <= 600 proper kpc (pkpc) and line-of-sight velocity offset Delta nu(g) <= 300 km s(-1) from the absorber. The closest is a massive, early-type galaxy at d = 41 pkpc that contains approximate to 70% of the total stellar mass identified at d <= 310 pkpc of the H-2 absorber. The close proximity of the H-2-bearing gas to the quiescent galaxy and the Fe-enhanced chemical abundance pattern of the absorber suggest a physical connection, in contrast to a picture in which DLAs are primarily associated with gas-rich dwarfs. This case study illustrates that deep galaxy redshift surveys are needed to gain insight into the diverse environments that host dense and potentially starforming gas.

This tarball collects the processed data that are included in Y. Chen et al, 2020, "The Keck Baryonic Structure Survey: Using foreground/background galaxy pairs to trace the structure and kinematics of circumgalactic neutral hydrogen at z~2".Here is how this file is organised. cats - KBSS catalogs as of Jan 2019, organized as FITS tables. This can be slightly different to the most recent KBSS catalog released at http://ramekin.caltech.edu/KBSS. lya_spec - The stacked spectra near Lya for the KGPS-Full and KGPS- zneb samples. Wavelengths are included as FITS-WCS in the header. The weight spectra are 1/sigma^2, estimated from bootstrap. These files are used to make Figure 5, and subsequently the 2D optical depth maps. wlya - Lya equivalent width as a function of impact parameter, stored as FITS tables. The table entries are, [dtran] - impact parameter; [dtran_lo] - lower edge of the "dtran" bins; [dtran_hi] - higher edge of the "dtran" bins; [ew] - Lya equivalent width; [ew_lo] - the lower 1-sigma limit of "ew"; [ew_hi] - the higher 1-sigma limit of "ew". These data are used to make Figure 6. tau_2d - 2D absorption maps, stored as multi-extension FITS files. [ext 0] - apparent optical depth; [ext 1] - 1-sigma error of ext 1; [ext 2] - dtran and vlos grids of ext 1 and 2. These are used to make Figures 7, 8, 9, 13, 14, 16, 17, 18. model - Best-fit model of the 2D absorption map, in multi-extension FITS. [ext 0] - modeled apparent optical depth; [ext 1] - grid. These are used to make Figure 13. Cite this record as:Chen, Y., Steidel, C., Hummels, C., Rudie, G., Dong, B., Trainor, R., Bogosavljevic, M., Erb, D., Pettini, M., Reddy, N., Shapley, A., Strom, A., Theios, R., Faucher-Giguere, C.-A., & Keres, D. (2020). KBSS Data: structure and kinematics of circumgalactic H I (Version 1.0) [Data set]. CaltechDATA. https://doi.org/10.22002/D1.1458 or choose a different citation style.Download Citation Unique Views: 14Unique Downloads: 1 between July 22, 2020 and July 12, 2021More info on how stats are collected Copyright: cc-zero

We present the discovery of neutral gas detected in both damped Ly alpha absorption (DLA) and H i 21 cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an H i bridge connecting two interacting dwarf galaxies (log (M (star)/M (circle dot)) = 8.5 +/- 0.2) that host a z = 0.026 DLA with log[N(H i)/cm(-2)] = 20.60 +/- 0.05 toward the QSO J2339-5523 (z (QSO) = 1.35). At impact parameters of d = 6 and 33 kpc, the dwarf galaxies have no companions more luminous than approximate to 0.05L (*) within at least Delta v = +/- 300 km s(-1) and d approximate to 350 kpc. The H i 21 cm emission is spatially coincident with the DLA at the 2 sigma-3 sigma level per spectral channel over several adjacent beams. However, H i 21 cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with a spin temperature to covering factor ratio T ( s )/f ( c ) > 1880 K). Observations with VLT-MUSE demonstrate that the alpha-element abundance of the ionized interstellar medium (ISM) is consistent with the DLA (approximate to 10% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf-dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and H i 21 cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.

We present a detailed study of two partial Lyman limit systems (pLLSs) of neutral hydrogen column density N-HI approximate to ( 1 - 3) x 10(16) 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 alpha-element abundance varying from [alpha/H] approximate to-0.8 to near solar and densities spanning over two decades from log n(H)/cm(-3) approximate to -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-star approximate to 2 x 10(10 )M(circle dot), 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-star approximate to 2 x 10(11) M-circle dot 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.

We present the first statistical analysis of kinematically resolved, spatially extended emission around z = 2-3 galaxies in the Keck Baryonic Structure Survey (KBSS) using the Keck Cosmic Web Imager (KCWI). Our sample of 59 star-forming galaxies (z(med) = 2.29) comprises the subset with typical KCWI integration times of similar to 5 h and with existing imaging data from the Hubble Space Telescope and/or adaptive optics-assisted integral field spectroscopy. The high-resolution images were used to evaluate the azimuthal dependence of the diffuse emission with respect to the stellar continuum within projected galactocentric distances of less than or similar to 30 proper kpc. We introduce cylindrically projected 2D spectra (CP2D) that map the averaged spectral profile over a specified range of azimuthal angle, as a function of impact parameter around galaxies. The averaged CP2D spectrum of all galaxies shows clear signatures of resonant scattering by outflowing gas. We stacked the CP2D spectra of individual galaxies over ranges of azimuthal angle with respect to their major axes. The extended emission along the galaxy principal axes is statistically indistinguishable, with residual asymmetry of <= 2 percent (similar to 2 sigma) of the integrated emission. The symmetry implies that the scattering medium is dominated by outflows in all directions within 30 kpc. Meanwhile, we find that the blueshifted component of emission is marginally stronger along galaxy minor axes for galaxies with relatively weak emission. We speculate that this weak directional dependence of emission becomes discernible only when the escape fraction is low. These discoveries highlight the need for similar analyses in simulations with radiative transfer modelling.

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 CII, CIII, NIII, MgII, SIII, SIIII, OII, OIII, OvI, and FeII absorption that span several hundred km s(-1) in line-of-sight velocity. Specifically, higher column density components (logN(HI)/cm(-2) greater than or similar to 16) in all four absorbers comprise dynamically cool gas with K and modest non-thermal broadening of 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 Hi 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 pc. While obtaining robust metallicity constraints for the low density, highly ionized phase remains challenging due to the uncertain , we demonstrate that the cool-phase gas in LLSs has a median metallicity of , with a 16-84 percentile range of [alpha/H] = (-1.3, -0.1). Furthermore, the wide range of inferred elemental abundance ratios ([C/alpha], [N/alpha], and [Fe/alpha]) 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.

The intergalactic medium (IGM) acts like a calorimeter recording energy injection by cosmic structure formation, shocks and photoheating from stars and active galactic nuclei. It was recently proposed that spatially inhomogeneous TeV-blazars could significantly heat up the underdense IGM, resulting in patches of both cold and warm IGM around z similar or equal to 2-3. The goal of this study is to compare predictions of different blazar heating models with recent observations of the IGM. We perform a set of cosmological simulations and carefully compute mock observables of the Lyman-alpha (Ly alpha) forest. We perform a detailed assessment of different systematic uncertainties which typically impact this type of observables and find that they are smaller than the differences between our models. We find that our inhomogeneous blazar heating model is in good agreement with the Ly alpha line properties and the rescaled flux probability distribution function at high redshift (2.5 < z < 3) but that our blazar heating models are challenged by lower redshift data (2 < z < 2.5). Our results could be explained by hell reionization although state-of-the-art models fall short on providing enough heating to the low-density IGM, thus motivating further radiative transfer studies of inhomogeneous hell reionization. If blazars are indeed hosted by group-mass haloes of 2 x 10(13)M(circle dot), a later onset of blazar heating in comparison with previous models would be favoured, which could bring our findings here in agreement with the evidence of blazar heating from local gamma-ray observations.