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it is now relatively well - established that @xmath650% of the present - day stellar mass has been formed since z=1 .
most of this stellar mass has been formed in intermediate - mass galaxies ( 3@xmath7 to 3@xmath8 , i.e. , @xmath6l@xmath9 galaxies ) , as a result of strong star formation episodes during which galaxies take the appearance of luminous infrared galaxies ( lirgs , see @xcite ) .
however , it is still unclear what physical processes have driven this evolution . to this respect ,
internal kinematics of distant galaxies is a powerful tracer of the major processes governing star - formation and galaxy evolution in the early universe such as merging , accretion , and feedback related to star - formation and agn . robustly measuring the internal kinematics of distant galaxies
is thus crucial for understanding how galaxies formed and evolved .
a large program at vlt entitled images ( intermediate mass galaxy evolution sequence ) is aiming to derive both resolved kinematics and integrated properties from vlt / giraffe and fors2 for galaxies selected in the chandra deep field ( cdfs ) , and to combine these observations with deep and high quality images from hst / acs as well as with deep mid - ir photometry from spitzer / mips .
this large program has now reached about 2/3 of its completion , and recently , 39 additional galaxies observed with giraffe have been analyzed @xcite .
combined with previous observations during the gto @xcite , it leads to a sample of 74 galaxies , which represents so far the largest existing sample of resolved kinematics for distant galaxies . because in images we have deliberately selected @xmath10@xmath11 galaxies ( i.e. , with stellar masses larger than 1.5@xmath210@xmath3m@xmath4 ) ,
we assume a similar limit for the combined sample . it let us with a sample of 63 galaxies which is well representative of the luminosity function at z=0.4 - 0.75 .
notice that the combined sample includes galaxies from 4 independent fields of view @xcite and is then unaffected by field - to - field variations within poisson statistics . within this redshift range ,
giraffe is able to recover the kinematics of almost all galaxies with @xmath12}})\ge15$] .
at large distances the spatial resolution is not sufficient to resolve the central regions of the galaxies .
it implies that the observed velocity dispersion ( @xmath13 ) of a rotational body is the convolution of the actual random motions with the rotation . for a rotationally supported galaxy
, it unavoidably leads to a well defined peak in the centre ( see fig .
1 ) . we have developed a classification scheme which allows us to compare any dispersion map to what it could be if it was a rotational disk @xcite .
discrepancy from a rotational body can be measured from differences in amplitude and in position of the @xmath13 peak between the pseudo rotational @xmath13 map and the observed one , which leads to a very robust diagnostic diagram for the 63 observed galaxies @xcite .    among the 63 galaxies of the representative sample , we find 20 rotating disks ( 32% ) ,
16 rotating disks with perturbations ( 25% ) and 27 galaxies with complex kinematics ( 43% , see fig . 1 and @xcite ) .
within this classification , perturbed rotations correspond to a discrepant @xmath13 peak from expectations for a pure rotation .
the complex kinematics class corresponds to objects for which the large scale motions are not aligned to the optical major axis , and show @xmath13 map very discrepant from expectations for a rotation ( see fig .
among these 63 galaxies , 52 have multi - band hst / acs imaging .
neichel et al .
( in prep . ) have constructed a new procedure to classify the morphology of distant galaxies .
this procedure relies on two important ingredients which are the used of color maps ( which helps to overcome limitations due to k - morphological corrections ) and the use of a visual decision tree .
this last ingredient is particularly important , as they have shown that automatic methods can overestimate the fraction of spirals by a factor of @xmath62 .
they find a relatively good agreement between the two classifications : most of rotating disks are classified as spirals , while most of galaxies having complex kinematics show a peculiar morphology .
combining morphology with spacially resolved kinematics allows us to study distant galaxies in very fine details : for the first time , we have recently detected a minor merger with a mass ratio of @xmath61:18 in a z@xmath60.6 galaxy classified as a perturbed rotator @xcite ( see fig .
[ fig3 ] ) .
such processes , which are predicted to be much more numerous than major mergers by numerical models , could provide us with a very plausible mecanism for explaining the kinematics of perturbed rotators .
let us now consider a representative sample of intermediate mass galaxies : at z=0.6 , 60% of galaxies have @xmath14)\ge15$]@xcite .
let us assume that quiescent ( @xmath14)<15$] ) galaxy are either rotationally or dispersion supported , thus minimising the fraction of galaxies with anomalous kinematics .
then our results imply that 42@xmath157% of z=0.4 - 0.75 galaxies have anomalous kinematics , including 26@xmath157% possessing complex kinematics . because up to 97% of local intermediate mass galaxies are
either e , s0 or spirals @xcite , it is likely that the fraction of anomalous kinematics is close to a few percents today .
this leads to an extremely rapid evolution of kinematical properties of galaxies , with about 10 times more complex kinematics about 6 gyr ago .
the observed evolution of the tully - fisher relation ( tfr ) provides us with a strong and independent confirmation .
it has been suggested that galaxies with non - relaxed kinematics ( pr and ck ) are responsible for the very large dispersions of the tfr at high redshift @xcite .
this result is confirmed by puech et al .
( in prep ) using the new sample of 63 galaxies : all the dispersion of the distant tfr can be accounted for by galaxies having non - relaxed kinematics .
so it is beyond doubt that kinematics is among the most rapidly evolving properties of galaxies .
which physical process could explain such a dramatic evolution ?
anomalous kinematics are linked with strong variations of the specific angular momentum consistent with a random walk evolution due to merging between galaxies , as predicted by the hierarchical scenario of galaxy formation @xcite . indeed , during a merger , and especially a major merger , galaxies pass through various stages during which the disk may be destroyed , generating significant discrepancies to the general behaviour of isolated rotating disks .
we do find a strong evolution of the galaxy kinematics since z=0.6 , with a significant fraction of galaxies with complex kinematics .
observations presented here tell us that major mergers could have played an important role in shaping galaxies as we observe them today .
indeed many estimates of the merger rate found that a typical intermediate mass galaxy should have experienced 0.5 to 0.75 major merger since z= 1 ( see @xcite and references therein ) , and most of them since z=2 - 3 .
a scenario in which merging is the dominant physical process explains many evolutionary features since z=1 , including the number density evolution of lirgs and the emergence of galaxies with complex morphologies and with blue cores at z@xmath16 0.4 @xcite .
it is moreover particularly in agreement with the fact that the milky way has had an exceptionally quiet merger history @xcite .
present - day @xmath17 galaxies being mostly spiral galaxies , it is unlikely that they have all escaped a major merging since z=2 - 3 .
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the large program images is near 2/3 of its completion . it provides us with kinematics ( giraffe deployable ifus ) , gas chemistry ( fors2 ) , detailed morphologies ( hst / acs ) and ir photometry ( spitzer ) for a set of 70 galaxies representative of intermediate mass galaxies ( @xmath0 @xmath1 -20.3 or 1.5@xmath210@xmath3m@xmath4 ) at z=0.4 - 0.75 . 
 we discover that , 6 gyr ago , a significant fraction of galaxies ( @xmath5 40% ) had anomalous kinematics , i.e. kinematics significantly discrepant from those of rotational or dispersion supported galaxies . 
 the anomalous kinematics cause the observed large dispersion of the tully - fisher relation at large distances . 
 images will soon allow us to study distant galaxies at a level of detail almost comparable to that of nearby galaxies .