A precise derivation of the evolution of the Tully Fisher is crucial to understand the interplay between dark matter and baryonic matter in cosmological models, using 15 deployable integral field units of FLAMES/GIRAFFE at VLT, we have recovered the velocity fields of 35 galaxies at intermediate redshift (0.4 < z < 0.75). This facility is able to recover the velocity fields of almost all the emission line galaxies with I AB ≤ 22.5 and W 0 (OII) ≥ 15 Å. In our sample, we find only 35% rotating disks. These rotating disks produce a Tully-Fisher relationship (stellar mass or M K versus V max ) which has apparently not evolved in slope, zero point and scatter since z = 0.6. The only evolution found is a brightening of the B band luminosity of a third of the disks, possibly due to an enhancement of the star formation. The very large scatters found in previously reported Tully-Fisher relationships at moderate redshifts are caused by the numerous (65%) galaxies with perturbed or complex kinematics. Those galaxies include minor or major mergers, merger remnants and/or inflow/outflows and their kinematics can be easily misidentified by slit spectroscopy. Their presence suggests a strong evolution in the dynamical properties of galaxies during the last 7 Gyr.

We compare both the Milky Way and M31 galaxies to local external disk galaxies within the same mass range, using their locations in the planes drawn by V flat versus M K (the Tully-Fisher relation), j disk (angular momentum), and the average Fe abundance, [Fe/ H ], of stars in the galaxy outskirts. We find, for all relationships, that the Milky Way is systematically offset by $1 , showing a significant deficiency in stellar mass, angular momentum, disk radius, and [Fe/ H ] in the stars in its outskirts at a given V flat . On the basis of their location in the (M K , V flat , and R d ) volume, the fraction of spirals like the Milky Way is 7% AE 1%, while M31 appears to be a ''typical'' spiral. Our galaxy appears to have escaped any significant merger over the last $10 Gyr, which may explain why it is deficient by a factor of 2Y3 in stellar mass, angular momentum, and outskirt metallicity, thus unrepresentative of the typical spiral. As with M31, most local spirals show evidence of a history shaped mainly by relatively recent merging. We conclude that the standard scenario of secular evolution driven by the accretion of gas and disk instabilities is generally unable to reproduce the properties of most (if not all) spiral galaxies. However, the so-called spiral-rebuilding scenario proposed two years ago by Hammer et al. is consistent with the properties of both distant galaxies and of their descendants, the local spirals.

Using the multi-integral field spectrograph GIRAFFE at VLT, we have derived the K-band Tully-Fisher relation (TFR) at z ∼ 0.6 for a representative sample of 65 galaxies with emission lines (W 0 (OII) ≥ 15 Å). We confirm that the scatter in the z ∼ 0.6 TFR is caused by galaxies with anomalous kinematics, and find a positive and strong correlation between the complexity of the kinematics and the scatter that they contribute to the TFR. Considering only relaxed-rotating disks, the scatter, and possibly also the slope, of the TFR, do not appear to evolve with redshift. We detect an evolution of the K-band TFR zero point between z ∼ 0.6 and z = 0, which, if interpreted as an evolution of the K-band luminosity of rotating disks, would imply that a brightening of 0.66 ± 0.14 mag occurs between z ∼ 0.6 and z = 0. Any disagreement with the results of Flores et al. (2006, A&A, 455, 107) are attributed to both an improvement of the local TFR and the more detailed accurate measurement of the rotation velocities in the distant sample. Most of the uncertainty can be explained by the relatively coarse spatial-resolution of the kinematical data. Because most rotating disks at z ∼ 0.6 are unlikely to experience further merging events, one may assume that their rotational velocity, which is taken as a proxy of the total mass, does not evolve dramatically. If true, our result implies that rotating disks observed at z ∼ 0.6 are rapidly transforming their gas into stars, to be able to double their stellar masses and be observed on the TFR at z = 0. The rotating disks observed are indeed emission-line galaxies that are either starbursts or LIRGs, which implies that they are forming stars at a high rate. Thus, a significant fraction of the rotating disks are forming the bulk of their stars within 6 to 8 Gyr, in good agreement with former studies of the evolution of the mass-metallicity relationship.

We have obtained deep spectroscopic observations of several nearby gamma-ray burst (GRB) host galaxies revealing for the first time the presence of Wolf-Rayet (WR) stars and numerous O stars located in rich and compact clusters or star forming regions. Surprisingly, high spatial resolution imaging shows that the GRBs and the associated supernovae did not occur in these regions, but several hundreds of parsec away. Considering various scenarios for GRB progenitors, we do not find any simple explanation of why they should be preferentially born in regions with low stellar densities. All the examined GRBs and associated SNe have occurred 400 to 800 pc from very high density stellar environments including large numbers of WR stars. Such distances can be travelled through at velocities of 100 km s −1 or larger, assuming the travel time to be the typical life time of WR stars. It leads us to suggest that GRB progenitors may be runaway massive stars ejected from compact massive star clusters. The ejection from such super star clusters may lead to a spin-up of these stars, producing the loss of the hydrogen and/or helium envelopes leading to the origin of the type Ibc supernovae associated with GRBs. If this scenario applies to all GRBs, it provides a natural explanation of the very small fraction of massive stars that emit a GRB at the end of their life. An alternative to this scenario could be a binary origin for GRBs, but this still requires an explanation of why it would preferentially occur in low stellar density regions.

The M31 haunted halo is likely associated with a rich merger history, currently assumed to be caused by multiple minor mergers. Here we use the GADGET2 simulation code to test whether M31 could have experienced a major merger in its past history. Our results indicate that a (3 ± 0.5):1 gaseous-rich merger with r pericenter = 25 ± 5 kpc and a polar orbit can explain many properties of M31 and of its halo. The interaction and fusion may have begun 8.75 ± 0.35 and 5.5 ± 0.5 Gyr ago, respectively. Observed fractions of the bulge and the thin and thick disks can be retrieved for a star formation history that is almost quiescent before the fusion. This also accords well with the observed relative fractions of intermediate age and old stars in both the thick disk and the Giant Stream. In this model, the Giant Stream is caused by returning stars from a tidal tail which contains material previously stripped from the satellite prior to the fusion. These returning stars are trapped into elliptical orbits or loops for long periods of time which can reach a Hubble time, and belong to a plane that is 45• offset from the M31 disk position angle. Because these streams of stars are permanently fed by new infalling stars with high energy from the tidal tail, we predict large loops which scale rather well with the features recently discovered in the M31 outskirts. We demonstrate that a single merger could explain first-order (intensity and size), morphological, and kinematical properties of the disk, thick disk, bulge, and streams in the halo of M31, as well as the observed distribution of stellar ages, and perhaps metallicities. This challenges the current scenarios assuming that each feature in the disk (the 10 kpc ring) or in its outskirts (thick disk, the Giant Stream, and the numerous streams) is associated with an equivalent number of minor mergers. Given the large number of parameters, further constraints are certainly required to better render the complexity of M31 and of the substructures within its halo which may ultimately lead to a more precise geometry of the encounter. This would allow us, in principle, to evaluate the impact of such a major event on the Andromeda system and the Local Group.

Recent observations of our neighbouring galaxy M31 have revealed that its disc was shaped by widespread events. The evidence for this includes the high dispersion (V/σ ≤ 3) of stars older than 2 Gyr, and a global star formation episode, 2–4 Gyr ago. Using the modern hydrodynamical code, gizmo, we have performed 300 high-resolution simulations to explore the extent to which these observed properties can be explained by a single merger. We find that the observed M31 disc resembles models having experienced a 4:1 merger, in which the nuclei coalesced 1.8–3 Gyr ago, and where the first passage took place 7–10 Gyr ago at a large pericentre distance (32 kpc). We also show that within a family of orbital parameters, the Giant Stream (GS) can be formed with various merger mass ratios, from 2:1 to 300:1. A recent major merger may be the only way to create the very unusual age–dispersion relation in the disc. It reproduces and explains the long-lived 10 kpc ring, the widespread and recent star formation event, the absence of a remnant of the GS progenitor, the apparent complexity of the 3D spatial distribution of the GS, the NE and G Clumps and their formation process, and the observed slope of the halo profile. These modelling successes lead us to propose that the bulk of the substructure in the M31 halo, as well as the complexity of the inner galaxy, may be attributable to a single major interaction with a galaxy that has now fully coalesced with Andromeda.

We investigate whether the Hubble sequence can be reproduced by the relics of merger events. We verify that, at z median = 0.65, the abundant population of anomalous starbursts -i.e. with peculiar morphologies and abnormal kinematics -is mainly linked to the local spirals. Their morphologies are dominated by young stars and are intimately related to their ionised-gas kinematics. We show that both morphologies and kinematics can be reproduced by using gas modelling from Barnes ' (2002, MNRAS, 333, 481) study of major mergers. Their gas content may be indirectly evaluated by assuming that distant starbursts follow the Kennicutt-Schmidt relation: the median gas fraction is found to be 31%. Using our modelling to estimate the gas-to-star transformation during a merger, we identify the gas fraction in the progenitors to be generally above 50%. All distant and massive starbursts can be distributed along a temporal sequence from the first passage to the nuclei fusion and then to the disk rebuilding phase. This later phase has been recently illustrated for J033245.11-274724.0, a distant compact galaxy dominated by a red, dust-enshrouded disk. This active production of rebuilt disks is in excellent agreement with model predictions for gaseous rich encounters. It confirms that the rebuilding spiral disk scenarioa strong and recent reprocessing of most disks by major mergers -is possibly an important channel for the formation of presentday disks in grand-design spirals. Because half of the present-day spirals had peculiar morphologies and anomalous kinematics at z median = 0.65, they could indeed have been in major merger phases 6 Gyr ago, and almost all at z ∼ 1. It is time now to study in detail the formation of spiral disks and of their substructures, including bulge, disks, arms, bars and rings that may mainly originate from instabilities created during the last major merger. Many galaxies also show a helicoidal structure, which is probably due to a central torque, and seems to play an important role in regulating the angular momentum of the newly-formed disks.

Nearly half the stellar mass of present-day spiral galaxies has formed since z = 1, and galaxy kinematics is an ideal tool to identify the underlying mechanisms responsible for the galaxy mass assembly since that epoch. Here, we present the first results of the ESO large program, "IMAGES", which aims at obtaining robust measurements of the kinematics of distant galaxies using the multi-IFU mode of GIRAFFE on the VLT. 3D spectroscopy is essential to robustly measure the often distorted kinematics of distant galaxies (e.g., Flores et al. 2006, A&A, 455, 107). We derive the velocity fields and σ-maps of 36 galaxies at 0.4 < z < 0. 10 M emission line galaxies in this redshift range, and are largely unaffected by cosmic variance. Taking into account all galaxies -with or without emission lines -in that redshift range, we find that at least 41 ± 7% of them have anomalous kinematics, i.e., they are not dynamically relaxed. This includes 26 ± 7% of distant galaxies with complex kinematics, i.e., they are not simply pressure or rotationally supported. Our result implies that galaxy kinematics are among the most rapidly evolving properties, because locally, only a few percent of the galaxies in this mass range have complex kinematics. It is well-established that galaxies undergoing a merger have complex large-scale motions and thus are likely responsible for the strong evolution of the galaxy kinematics that we observe.