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 AC114 .
Metal absorption lines are detected and observed to be blueshifted by 300-800 km s ^ { -1 } with respect to the centroid of Ly- \alpha 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 Ly- \alpha emission with redshift , which may be a genuine evolutionary effect towards 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 , nor 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 , \sim 0.5-5 kpc h ^ { -1 } for a flat cosmology with \Omega _ { m } = 0.3 , \Omega _ { \Lambda } = 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 \sim 20 \times are inferred .
Two objects show a clear spatial extension of the Ly- \alpha 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 .