We present new results on the kinematics and spatial distribution of metal-enriched gas within ∼ 125 kpc of star-forming ("Lyman Break") galaxies at redshifts 2 < ∼ z < ∼ 3. In particular, we focus on constraints provided by the rest-frame far-UV spectra of faint galaxies-and demonstrate how galaxy spectra can be used to obtain key spatial and spectral information more efficiently than possible with QSO sightlines. Using a sample of 89 galaxies with z = 2.3 ± 0.3 and with both rest-frame far-UV and Hα spectra, we re-calibrate the measurement of accurate galaxy systemic redshifts using only survey-quality rest-UV spectra. We use the velocity-calibrated sample to investigate the kinematics of the galaxy-scale outflows via the strong interstellar (IS) absorption lines and Lyman α emission (when present), as well as their dependence on other physical properties of the galaxies. We construct a sample of 512 close (1 − 15 ′′ ) angular pairs of z ∼ 2 − 3 galaxies with redshift differences indicating a lack of physical association. Sightlines to the background galaxies provide new information on the spatial distribution of circumgalactic gas surrounding the foreground galaxies. The close pairs sample galactocentric impact parameters 3-125 kpc (physical) at z = 2.2, providing for the first time a robust map of cool gas as a function of galactocentric distance for a well-characterized population of galaxies. We propose a simple model of circumgalactic gas that simultaneously matches the kinematics, depth, and profile shape of IS absorption and Lyα emission lines, as well as the observed variation of absorption line strength (H I and several metallic species) versus galactocentric impact parameter. Within the model, cool gas is distributed symmetrically around every galaxy, accelerating radially outward with v out (r) increasing with r (i.e., the highest velocities are located at the largest galactocentric distances r). The inferred radial dependence of the covering fraction of cool gas (which modulates the absorption line strength) is f c (r) ∝ r −γ with 0.2 < ∼ γ < ∼ 0.6 depending on transition. We discuss the results of the observations in the context of "cold accretion", in which cool gas is accreting via filamentary streams directly onto the central regions of galaxies. At present, we find little observational evidence for cool infalling material, while evidence supporting the large-scale effects of superwind outflows is strong. This "pilot" study using faint galaxy spectra demonstrates the potential of using galaxies to trace baryons within galaxies, in the circumgalactic medium, and ultimately throughout the IGM.

Using a sample of 92 UV continuum-selected, spectroscopically identified galaxies with z = 2.65, all of which have been imaged in the Lyα line with extremely deep narrow-band imaging, we examine galaxy Lyα emission profiles to very faint surface brightness limits. The galaxy sample is representative of spectroscopic samples of Lyman break galaxies (LBGs) at similar redshifts in terms of apparent magnitude, UV luminosity, inferred extinction, and star formation rate and was assembled without regard to Lyα emission properties. Approximately 45% (55%) of the galaxy spectra have Lyα appearing in net absorption (emission), with 20% satisfying commonly used criteria for the identification of "Lyα emitters" (LAEs; W 0 (Lyα) 20 Å). We use extremely deep stacks of rest-UV continuum and continuum-subtracted Lyα images to show that all sub-samples exhibit diffuse Lyα emission to radii of at least 10 (∼80 physical kpc). The characteristic exponential scale lengths for Lyα line emission exceed that of the λ 0 = 1220 Å UV continuum light by factors of ∼5-10. The surface brightness profiles of Lyα emission are strongly suppressed relative to the UV continuum light in the inner few kpc, by amounts that are tightly correlated with the galaxies' observed spectral morphology; however, all galaxy sub-subsamples, including that of galaxies for which Lyα appears in net absorption in the spectra, exhibit qualitatively similar diffuse Lyα emission halos. Accounting for the extended Lyα emission halos, which generally would not be detected in the slit spectra of individual objects or with typical narrow-band Lyα imaging, increases the total Lyα flux (and rest equivalent width W 0 (Lyα)) by an average factor of ∼5, and by a much larger factor for the 80% of LBGs not classified as LAEs. We argue that most, if not all, of the observed Lyα emission in the diffuse halos originates in the galaxy H ii regions but is scattered in our direction by H i gas in the galaxy's circum-galactic medium. The overall intensity of Lyα halos, but not the surface brightness distribution, is strongly correlated with the emission observed in the central ∼1 -more luminous halos are observed for galaxies with stronger central Lyα emission. We show that whether or not a galaxy is classified as a giant "Lyα blob" (LAB) depends sensitively on the Lyα surface brightness threshold reached by an observation. Accounting for diffuse Lyα halos, all LBGs would be LABs if surveys were sensitive to 10 times lower Lyα surface brightness thresholds; similarly, essentially all LBGs would qualify as LAEs.

We present results of a deep spectroscopic survey quantifying the statistics of the escape of hydrogen-ionizing photons from star-forming galaxies at z ∼ 3. The Keck Lyman Continuum Spectroscopic Survey (KLCS) includes spectra of 124 galaxies with z = 3.05 ± 0.18 and −22.1 ≤ M uv ≤ −19.5, observed in 9 independent fields, covering a common rest-wavelength range 880 ≤ λ 0 /Å < ∼ 1750. We measure the ratio of ionizing to non-ionizing UV flux density f 900 / f 1500 obs , where f 900 is the mean flux density evaluated over the range λ 0 = [880, 910] Å. To quantify f 900 / f 1500 out -the emergent ratio of ionizing to non-ionizing UV flux density -we use detailed Monte Carlo modeling of the opacity of H I in the intergalactic (IGM) and circumgalactic (CGM) medium as a function of source redshift. By analyzing high-S/N composite spectra formed from sub-samples exhibiting common observed properties and numbers sufficient to reduce the uncertainty in the IGM+CGM correction, we obtain precise values of f 900 / f 1500 out , including a full-sample average f 900 / f 1500 out = 0.057 ± 0.006. We further show that f 900 / f 1500 out increases monotonically with Lyα rest equivalent width W λ (Lyα), inducing an inverse correlation with UV luminosity as a by-product. To connect LyC leakage to intrinsic galaxy properties, we fit the composite spectra using stellar population synthesis (SPS) together with simple models of the ISM in which a fraction f c of the stellar continuum is covered by optically-thick gas with column density N HI . We show that the composite spectra simultaneously constrain the intrinsic properties of the ionizing stars (L 900 /L 1500 ) int along with f c , N HI , E(B − V ), and f esc,abs , the escape fraction of ionizing photons. We find a sample-averaged f esc,abs = 0.09 ± 0.01, and that subsamples fall along a linear relation f esc,abs 0.75 W λ (Lyα)/(110 Å) for 0 ≤ W λ (Lyα) < ∼ 60; subsamples with W λ (Lyα) < 0 have f esc,abs consistent with zero. We use the FUV luminosity function, the distribution function n[W λ (Lyα)], and the relationship between W λ (Lyα) and f 900 / f 1500 out to estimate the total ionizing emissivity of z ∼ 3 star-forming galaxies with M UV ≤ −19.5: LyC 6 × 10 24 ergs s −1 Hz −1 Mpc −3 . This value exceeds the contribution of QSOs by a factor of ∼ 1.2 − 3.7, and accounts for > ∼ 50% of the total LyC estimated using indirect methods at z ∼ 3. 11 According to Becker et al. (2011), continuum blanketing from the Lyman α forest increases ∝ (1 + z) 2.8 over the redshift range 2.1 < ∼ zs < ∼ 5.5.

We present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey of the distant universe designed to explore the details of the connection between galaxies and intergalactic baryons within the same survey volumes, focusing particularly on scales from ∼ 50 kpc to a few Mpc. The KBSS is optimized for the redshift range z ∼ 2 − 3, combining S/N∼ 100 Keck/HIRES spectra of 15 of the brightest QSOs in the sky at z ≃ 2.5 − 2.9 with very densely sampled galaxy redshift surveys within a few arcmin of each QSO sightline. In this paper, we present quantitative results on the distribution, column density, kinematics, and absorber line widths of neutral hydrogen (H I) surrounding a subset of 886 KBSS star-forming galaxies with 2.0 < ∼ z < ∼ 2.8 and with projected distances ≤ 3 physical Mpc from a QSO sightline. Using Voigt profile decompositions of the full Lyα forest region of all 15 QSO spectra, we compiled a catalog of ∼ 6000 individual absorbers in the redshift range of interest, with 12 ≤log(N HI )≤ 21. These are used to measure H I absorption statistics near the redshifts of foreground galaxies as a function of projected galactocentric distance from the QSO sightline and for randomly chosen locations in the intergalactic medium (IGM) within the survey volume. We find that N HI and the multiplicity of velocity-associated H I components increase rapidly with decreasing galactocentric impact parameter and as the systemic redshift of the galaxy is approached. The strongest H I absorbers within ≃ 100 physical kpc of galaxies have N HI ∼ 3 orders of magnitude higher than those near random locations in the IGM. The circumgalactic zone of most significantly enhanced H I absorption is found within transverse distances of < ∼ 300 kpc and within ±300 km s −1 of galaxy systemic redshifts. Taking this region as the defining bounds of the circumgalactic medium (CGM), nearly half of absorbers with log(N HI ) > 15.5 are found within the CGM of galaxies meeting our photometric selection criteria, while their CGM occupy only 1.5% of the cosmic volume. The spatial covering fraction, multiplicity of absorption components, and characteristic N HI remain significantly elevated to transverse distances of ∼2 physical Mpc from galaxies in our sample. Absorbers with N HI > 10 14.5 cm −2 are tightly correlated with the positions of galaxies, while absorbers with lower N HI are correlated with galaxy positions only on > ∼ Mpc scales. Redshift anisotropies on these larger scales indicate coherent infall toward galaxy locations, while on scales of ∼ 100 physical kpc peculiar velocities of ∆v ≃ ±260 km s −1 with respect to the galaxies are indicated. The median Doppler widths of individual absorbers within 1-3 r vir of galaxies are larger by ≃ 50% than randomly chosen absorbers of the same N HI , suggesting higher gas temperatures and/or increased turbulence likely caused by some combination of accretion shocks and galactic winds around galaxies with M halo ≃ 10 12 M ⊙ at z ∼ 2 − 3.