MASSIV: Mass Assembly Survey with SINFONI in VVDS - II. Kinematics and
  close environment classification
  (Abridged) Processes driving mass assembly are expected to evolve on
different timescales along cosmic time. A transition might happen around z ~ 1
as the cosmic star formation rate starts its decrease. Identifying the
dynamical nature of galaxies on a representative sample is necessary to infer
and compare the mass assembly mechanisms across cosmic time. We present an
analysis of the kinematics properties of 50 galaxies with 0.9 < z < 1.6 from
the MASSIV sample observed with SINFONI/VLT with 4.5x10^9 Msun < M < 1.7x10^11
Msun and 6 Msun/yr < SFR < 300 Msun/yr. This is the largest sample with
2D-kinematics in this redshift range. We provide a classification based on
kinematics as well as on close galaxy environment. We find that 29% of galaxies
are experiencing merging or have close companions that may be gravitationally
linked. This is placing a lower limit on the fraction of interacting galaxies.
We find that at least 44% of the galaxies display ordered rotation whereas at
least 35% are non-rotating objects. All rotators except one are compatible with
rotation-dominated (Vmax/sigma > 1) systems. Non-rotating objects are mainly
small objects (Re < 4 kpc). Combining our sample with other 3D-spectroscopy
samples, we find that the local velocity dispersion of the ionized gas
component decreases continuously from z ~ 3 to z = 0. The proportion of disks
also seems to be increasing in star-forming galaxies when the redshift
decreases. The number of interacting galaxies seems to be at a maximum at z ~
1.2. These results draw a picture in which cold gas accretion may still be
efficient at z ~ 1.2 but in which mergers may play a much more significant role
at z ~ 1.2 than at higher redshift. From a dynamical point of view, the
redshift range 1 < z < 2 therefore appears as a transition period in the galaxy
mass assembly process.
