Clumpy galaxies at z~0.6: kinematics, stability, and comparison with
  analogs at other redshifts
  Distant clumpy galaxies are thought to be Jeans-unstable disks, and an
important channel for the formation of local galaxies, as suggested by recent
spatially-resolved kinematic observations of z~2 galaxies. I study the
kinematics of clumpy galaxies at z~0.6, and compare their properties with those
of counterparts at higher and lower redshifts. I selected a sample of 11 clumpy
galaxies at z~0.6 from the representative sample of emission line,
intermediate-mass galaxies IMAGES. Selection was based on rest-frame UV
morphology from HST/ACS images, mimicking the selection criteria commonly used
at higher redshifts. Their spatially-resolved kinematics were derived in the
frame of the IMAGES survey, using the VLT/FLAMES-GIRAFFE multi-integral field
spectrograph. For those showing large-scale rotation, I derived the Toomre Q
parameter, which characterizes the stability of their gaseous and stellar
phases. I find that the fraction of UV-selected clumpy galaxies at z~0.6 is
20+/-12%. Roughly half of them (45+/-30%) have complex kinematics inconsistent
with Jeans-unstable disks, while those in the remaining half (55+/-30%) show
large-scale rotations. The latter reveal a stable gaseous phase, but the
contribution of their stellar phase makes them globally unstable to clump
formation. Clumpy galaxies appear to be less unstable at z~0.6 than at z~2,
which could explain why the UV clumps tend to vanish in rest-frame optical
images of z~0.6 clumpy galaxies, conversely to z~2 clumpy galaxies, in which
the stellar phase can substantially fragment. This suggests that the former
correspond to patchy star-formation regions superimposed on a smoother mass
distribution. A possible and widespread scenario for driving clump formation
relies on instabilities by cold streams penetrating the dark matter halos where
clumpy galaxies inhabit. While such a gas accretion process is predicted to be
significant in massive, z~2 haloes, it is also predicted to be strongly
suppressed in similar, z~0.6 haloes, which could explain why lowest-z clumpy
galaxies appear to be driven by a different mechanism. Instead, I found that
interactions are probably the dominant driver leading to the formation of
clumpy galaxies at z<1. I argue that the nature of z>1 clumpy galaxies remains
more uncertain. While cold flows could be an important driver at z~2, I also
argue that the observed and cumulative merger fraction between z=2 and z=3 is
large enough so that every z~2 galaxy might be the result of a merger that
occurred within their past 1 Gyr. I conclude that it is premature to rule out
mergers as a universal driver for galaxy evolution from z~2 down to z=0.
