Lyman break galaxy close and interacting pairs at z ~ 3
  To date, the identification of interactions at z ~ 3 and above has relied on
morphological analysis. Here, we present five serendipitous spectroscopic z ~ 3
Lyman break galaxy (LBG) pairs with projected proper separations < 15 h^-1 kpc
in our survey of nine separate Keck fields. The data consist of 140 of our
highest signal-to-noise ratio LBG spectra and ~500 of our most confident
colour-selected LBGs. We show that the pairs are composed of two distinct close
and/or interacting LBGs from a detailed analysis of the rest-frame ultraviolet
spectra and images. In addition, we show that the pair number and separation
distribution is expected from (1) the angular correlation function when applied
to our survey and ~2500 colour-selected LBGs from the literature and (2) an
analysis of a carefully matched high-resolution hybrid numerical and analytical
cosmological simulation. Because the spectroscopic slitlets have random
orientations with respect to the close pairs on the sky, the serendipitous
pairs provide an unbiased sampling of the underlying close pair fraction.
Finally, we discover two Ly-a emitters (LAEs) in our slitlets and find that
they reside within 50 projected h^-1 kpc of LBGs. In this work, we uncover a
strong relationship between Ly-a emission and pair separation. All confirmed
and all candidate LBG pairs with separations of < 15 projected h^-1 kpc exhibit
Ly-a in emission and we find an overabundance of Ly-a emission in pairs with <
50 projected h^-1 kpc separations. This relationship suggests a picture in
which a measurable fraction of the Ly-a emission of LBGs, and potentially LAEs,
is generated via interaction mechanisms. As a result, serendipitous
spectroscopic close pairs provide a unique means to help identify and study
high-redshift galaxy interactions using conventional ground-based optical data.
