We report the discovery of a substantial population of star-forming galaxies at 3.0 < ∼ z < ∼ 3.5. These galaxies have been selected using color criteria sensitive to the presence of a Lyman continuum break superposed on an otherwise very blue far-UV continuum, and then confirmed with deep spectroscopy on the W. M. Keck telescope. The surface density of galaxies brighter than R = 25 with 3.0 < ∼ z < ∼ 3.5 is 0.4 ± 0.07 galaxies arcmin −2 , approximately 1.3% of the deep counts at these magnitudes; this value applies both to "random" fields and to fields centered on known QSOs. The corresponding co-moving space density is approximately half that of luminous (L > ∼ L * ) present-day galaxies. Our sample of z > 3 galaxies is large enough that we can begin to detail the spectroscopic characteristics of the population as a whole. The spectra of the z > 3 galaxies are remarkably similar to those of nearby star-forming galaxies, the dominant features being strong low-ionization interstellar absorption lines and highionization stellar lines, often with P-Cygni profiles characteristic of Wolf-Rayet and O-star winds. Lyman α emission is generally weak (< 20Å rest equivalent width) and is absent for >50% of the galaxies. We assign approximate mass scales to the galaxies using the strengths of the heavily saturated interstellar features and find that, if the line widths are dominated by gravitational motions within the galaxies, the implied velocity dispersions are 180 ≤ σ ≤ 320 km s −1 , in the range expected for massive galaxies. The star formation rates, which can be measured directly from the far-UV continua, lie in the range 4 − 25 h −2 50 M ⊙ yr −1 (for q 0 = 0.5), with 8.5h −2 50 M ⊙ yr −1 being typical. Together with the morphological properties of the z > 3 galaxy population, which we discuss in a 1 Based in large part on observations obtained at the W.M. Keck Observatory, which is operated jointly by the

Observations of reionization-era analogs at z ∼ 3 are a powerful tool for constraining reionization. Rest-ultraviolet observations are particularly useful, in which both direct and indirect tracers of ionizing-photon production and escape can be observed. We analyse a sample of 124 z ∼ 3 galaxies from the Keck Lyman Continuum Spectroscopic Survey, with sensitive spectroscopic measurements of the Lyman continuum region. We present a method of removing foreground contamination from our sample using high-resolution, multi-band Hubble Space Telescope imaging. We re-measure the global properties of the cleaned sample of 13 individually-detected Lyman continuum sources and 107 individually-undetected sources, including a sample-averaged absolute escape fraction of fesc, abs = 0.06 ± 0.01 and a sample-averaged ratio of ionizing to non-ionizing ultraviolet flux density of 〈f900/f1500〉out = 0.040 ± 0.006, corrected for attenuation from the intergalactic and circumgalactic media. Based on composite spectra, we also recover a strong positive correlation between 〈f900/f1500〉out and Lyα equivalent width (Wλ(Ly$\rm \alpha$)) and a negative correlation between 〈f900/f1500〉out and UV luminosity. As in previous work, we interpret the relationship between 〈f900/f1500〉out and Wλ(Ly$\rm \alpha$) in terms of the modulation of the escape of ionizing radiation from star-forming galaxies based on the covering fraction of neutral gas. We also use a Wλ(Ly$\rm \alpha$)-weighted 〈f900/f1500〉out to estimate an ionizing emissivity from star-forming galaxies at z ∼ 3 as εLyC ≃ 5.5 × 1024 erg s−1 Hz−1 Mpc−3. This estimate, evaluated using the uncontaminated sample of this work, affirms that the contribution of galaxies to the ionizing background at z ∼ 3 is comparable to that of active galactic nuclei.

We report the results of analyses of galactic outflows in a sample of 45 low-redshift starburst galaxies in the COS Legacy Archive Spectroscopic SurveY (CLASSY), augmented by five additional similar starbursts with Cosmic Origins Spectrograph (COS) data. The outflows are traced by blueshifted absorption lines of metals spanning a wide range of ionization potential. The high quality and broad spectral coverage of CLASSY data enable us to disentangle the absorption due to the static interstellar medium (ISM) from that due to outflows. We further use different line multiplets and doublets to determine the covering fraction, column density, and ionization state as a function of velocity for each outflow. We measure the outflow’s mean velocity and velocity width, and find that both correlate in a highly significant way with the star formation rate, galaxy mass, and circular velocity over ranges of four orders of magnitude for the first two properties. We also estimate outflow rates of metals, mass, momentum, and kinetic energy. We find that, at most, only about 20% of silicon created and ejected by supernovae in the starburst is carried out in the warm phase we observe. The outflows’ mass-loading factor increases steeply and inversely with both circular and outflow velocity (log–log slope ∼−1.6), and reaches ∼10 for dwarf galaxies. We find that the outflows typically carry about 10%–100% of the momentum injected by massive stars and about 1%–20% of the kinetic energy. We show that these results place interesting constraints on, and new insights into, models and simulations of galactic winds.