Spectral evidence for widespread galaxy outflows at z > 4

We present discovery spectra of a sample of eight lensed galaxies at high redshift, 3.7 < z < 5.2, selected by their red colors in the fields of four massive clusters: A1689, A2219, A2390, and AC 114. Metal absorption lines are detected and observed to be blueshifted by 300-800 km s^-1 with respect to the centroid of Lyα emission. A correlation is found between this blueshift and the equivalent width of the metal lines, which we interpret as a broadening of saturated absorption lines caused by a dispersion in the outflow velocity of interstellar gas. Local starburst galaxies show similar behavior, associated with obvious gas outflows. We also find a trend of increasing equivalent width of Lyα emission with redshift, which may be a genuine evolutionary effect toward younger stellar populations at high redshift with less developed stellar continua. No obvious emission is detected below the Lyman limit in any of our spectra or in deep U- or B-band images. The UV continua are reproduced well by early B stars, although some dust absorption would allow a fit to hotter stars. If B stars dominate, then their relatively prominent stellar absorption lines should separate in wavelength from those of the outflowing gas, requiring more detailed spectroscopy. After correcting for the lensing, we derive small physical sizes for our objects, ∼0.5-5 kpc h^-1 for a flat cosmology with Ω_m = 0.3, Ω _Λ = 0.7. The lensed images are only marginally resolved in good seeing despite their close proximity to the critical curve, where large arcs are visible and hence high magnifications of up to ∼20 times are inferred. Two objects show a clear spatial extension of the Lyα emission relative to the continuum starlight, indicating a "breakout" of the gas. The sizes of our galaxies together with their large gas motion suggests that outflows of gas are common at high redshift and associated with galaxy formation.