The role of major mergers in shaping galaxies at 2<z<4 in the VUDS and
  VVDS surveys
  The mass assembly of galaxies can proceed through different physical
processes. Here we report on the spectroscopic identification of close physical
pairs of galaxies at redshifts 2 <z < 4 and discuss the impact of major mergers
in shaping galaxies at these early cosmological times. We aim to identify and
characterize close physical pairs of galaxies destined to merge and use their
properties to infer the contribution of merging processes to the early mass
assembly of galaxies. We search for galaxy pairs with a transverse separation
r_p < 25 h^{-1} kpc and a velocity difference Delta v < 500 km s^{-1} using the
VIMOS VLT Deep Survey (VVDS) and early data from the VIMOS Ultra Deep Survey
(VUDS) that comprise a sample of 1111 galaxies with spectroscopic redshifts
measurements at redshifts 1.8 < z < 4 in the COSMOS, ECDFS, and VVDS-02h
fields. We analyse their spectra and associated visible and near-infrared
photometry to assess the main properties of merging galaxies that have an
average stellar mass M_{star}=2.3 x 10^{10} M_{sun} at these redshifts. Using
the 12 physical pairs found in our sample we obtain a first estimate of the
merger fraction at these rdshifts, fmerg ~(15-20)%. The pair separations
indicate that these pairs will merge within 1 Gyr, on average, with each
producing a more massive galaxy by the time the cosmic star formation peaks at
z~1-2. From the average mass ratio between galaxies in the pairs, the stellar
mass of the resulting galaxy after merging will be ~60% larger than the most
massive galaxy in the pair before merging. We conclude that major merging of
galaxy pairs is on-going at 2<z<4 and significantly contributing to the major
assembly phase of galaxies at this early epoch.
