We present the MUSE Hubble Ultra Deep Survey, a mosaic of nine MUSE fields covering 90% of the entire HUDF region with a 10-h deep exposure time, plus a deeper 31-h exposure in a single 1.15 arcmin 2 field. The improved observing strategy and advanced data reduction results in datacubes with sub-arcsecond spatial resolution (0 . 65 at 7000 Å) and accurate astrometry (0 . 07 rms). We compare the broadband photometric properties of the datacubes to HST photometry, finding a good agreement in zeropoint up to m AB = 28 but with an increasing scatter for faint objects. We have investigated the noise properties and developed an empirical way to account for the impact of the correlation introduced by the 3D drizzle interpolation. The achieved 3σ emission line detection limit for a point source is 1.5 and 3.1 × 10 −19 erg s −1 cm −2 for the single ultra-deep datacube and the mosaic, respectively. We extracted 6288 sources using an optimal extraction scheme that takes the published HST source locations as prior. In parallel, we performed a blind search of emission line galaxies using an original method based on advanced test statistics and filter matching. The blind search results in 1251 emission line galaxy candidates in the mosaic and 306 in the ultradeep datacube, including 72 sources without HST counterparts (m AB > 31). In addition 88 sources missed in the HST catalog but with clear HST counterparts were identified. This data set is the deepest spectroscopic survey ever performed. In just over 100 h of integration time, it provides nearly an order of magnitude more spectroscopic redshifts compared to the data that has been accumulated on the UDF over the past decade. The depth and high quality of these datacubes enables new and detailed studies of the physical properties of the galaxy population and their environments over a large redshift range.

We observed Hubble Deep Field South with the new panoramic integral-field spectrograph MUSE that we built and have just commissioned at the VLT. The data cube resulting from 27 h of integration covers one arcmin 2 field of view at an unprecedented depth with a 1σ emission-line surface brightness limit of 1 × 10 −19 erg s −1 cm −2 arcsec −2 , and contains ∼90 000 spectra. We present the combined and calibrated data cube, and we performed a first-pass analysis of the sources detected in the Hubble Deep Field South imaging. We measured the redshifts of 189 sources up to a magnitude I 814 = 29.5, increasing the number of known spectroscopic redshifts in this field by more than an order of magnitude. We also discovered 26 Lyα emitting galaxies that are not detected in the HST WFPC2 deep broad-band images. The intermediate spectral resolution of 2.3 Å allows us to separate resolved asymmetric Lyα emitters, [O ]3727 emitters, and C ]1908 emitters, and the broad instantaneous wavelength range of 4500 Å helps to identify single emission lines, such as [O ]5007, Hβ, and Hα, over a very wide redshift range. We also show how the three-dimensional information of MUSE helps to resolve sources that are confused at ground-based image quality. Overall, secure identifications are provided for 83% of the 227 emission line sources detected in the MUSE data cube and for 32% of the 586 sources identified in the HST catalogue. The overall redshift distribution is fairly flat to z = 6.3, with a reduction between z = 1.5 to 2.9, in the well-known redshift desert. The field of view of MUSE also allowed us to detect 17 groups within the field. We checked that the number counts of [O ]3727 and Lyα emitters are roughly consistent with predictions from the literature. Using two examples, we demonstrate that MUSE is able to provide exquisite spatially resolved spectroscopic information on the intermediate-redshift galaxies present in the field. This unique data set can be used for a wide range of follow-up studies. We release the data cube, the associated products, and the source catalogue with redshifts, spectra, and emission-line fluxes.

Star-forming disk galaxies at high redshift are often subject to violent disk instability, characterized by giant clumps whose fate is yet to be understood. The main question is whether the clumps disrupt within their dynamical timescale (≤ 50 Myr), like the molecular clouds in today's galaxies, or whether they survive stellar feedback for more than a disk orbital time (≈ 300 Myr) in which case they can migrate inward and help building the central bulge. We present 3.5-7 pc resolution AMR simulations of high-redshift disks including photo-ionization, radiation pressure, and supernovae feedback. Our modeling of radiation pressure determines the mass loading and initial velocity of winds from basic physical principles. We find that the giant clumps produce steady outflow rates comparable to and sometimes somewhat larger than their star formation rate, with velocities largely sufficient to escape galaxy. The clumps also lose mass, especially old stars, by tidal stripping, and the stellar populations contained in the clumps hence remain relatively young (≤ 200 Myr), as observed. The clumps survive gaseous outflows and stellar loss, because they are wandering in gas-rich turbulent disks from which they can re-accrete gas at high rates compensating for outflows and tidal stripping, overall keeping realistic and self-regulated gaseous and stellar masses. Our simulations produce gaseous outflows with velocities, densities and mass loading consistent with observations, and at the same time suggest that the giant clumps survive for hundreds of Myr and complete their migration to the center of highredshift galaxies, without rapid dispersion and reformation of clumps. These long-lived clumps can be involved in inside-out evolution and thickening of the disk, spheroid growth and fueling of the central black hole.

Context. Identifying the main processes of galaxy assembly at high redshifts is still a major issue in understanding galaxy formation and evolution at early epochs in the history of the Universe. Aims. This work aims to provide a first insight into the dynamics and mass assembly of galaxies at redshifts 1.2 < z < 1.6, the early epoch just before the sharp decrease of the cosmic star formation rate. Methods. We use the near-infrared integral field spectrograph SINFONI on the ESO-VLT under 0.65 seeing to obtain spatially resolved spectroscopy on nine emission line galaxies with 1.2 ≤ z ≤ 1.6 from the VIMOS VLT Deep Survey. We derive the velocity fields and velocity dispersions on kpc scales using the Hα emission line. Results. Out of the nine star-forming galaxies, we find that galaxies are distributed in three groups: two galaxies can be well reproduced by a rotating disk, three systems can be classified as major mergers and four galaxies show disturbed dynamics and high velocity dispersion. We argue that there is evidence for hierarchical mass assembly from major merging, with most massive galaxies with M > 10 11 M subject to at least one major merger over a 3 Gyr period as well as for continuous accretion feeding strong star formation. Conclusions. These results point towards a galaxy formation and assembly scenario which involves several processes, possibly acting in parallel, with major mergers and continuous gas accretion playing a major role. Well controlled samples representative of the bulk of the galaxy population at this key cosmic time are necessary to make further progress.

Due to their large distances, high‐redshift galaxies are observed at a very low spatial resolution. In order to disentangle the evolution of galaxy kinematics from low‐resolution effects, we have used Fabry–Pérot 3D Hα data cubes of 153 nearby isolated galaxies selected from the Gassendi Hα survey of SPirals (GHASP) to simulate data cubes of galaxies at redshift z= 1.7 using a pixel size of 0.125 arcsec and a 0.5 arcsec seeing. We have derived Hα flux, velocity and velocity dispersion maps. From these data, we show that the inner velocity gradient is lowered and is responsible for a peak in the velocity dispersion map. This signature in the velocity dispersion map can be used to make a kinematical classification, but misses 30 per cent of the regular rotating discs in our sample. Toy models of rotating discs have been built to recover the kinematical parameters and the rotation curves from low‐resolution data. The poor resolution makes the kinematical inclination uncertain and the position of galaxy centre difficult to recover. The position angle of the major axis is retrieved with an accuracy higher than 5° for 70 per cent of the sample. Toy models also enable us to retrieve statistically the maximum velocity and the mean velocity dispersion of galaxies with a satisfying accuracy. This validates the use of the Tully–Fisher relation for high‐redshift galaxies, but the loss of resolution induces a lower slope of the relation despite the beam smearing corrections. We conclude that the main kinematic parameters are better constrained for galaxies with an optical radius at least as large as three times the seeing. The simulated data have been compared to actual high‐redshift galaxy data observed with VLT/SINFONI, Keck/OSIRIS and VLT/GIRAFFE in the redshift range 3 > z > 0.4, allowing us to follow galaxy evolution from 11 to 4 Gyr. For rotation‐dominated galaxies, we find that the use of the velocity dispersion central peak as a signature of rotating discs may misclassify slow and solid body rotators. This is the case for ∼30 per cent of our sample. We show that the projected local data cannot reproduce the high velocity dispersion observed in high‐redshift galaxies except when no beam smearing correction is applied. This unambiguously means that, unlike local evolved galaxies, there exists at high redshift at least a population of disc galaxies for which a large fraction of the dynamical support is due to random motions. We should nevertheless ensure that these features are not due to important selection biases before concluding that the formation of an unstable and transient gaseous disc is a general galaxy formation process.

Context. 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. Aims. We aim to identify the dynamical nature of galaxies in a representative sample to be able to infer and compare the mass assembly mechanisms across cosmic time.Methods. We present an analysis of the kinematics properties of 50 galaxies with redshifts 0.9 < z < 1.6 from the MASSIV sample observed with SINFONI/VLT with a mass range from 4.5 × 10 9 M to 1.7 × 10 11 M and a star formation rate from 6 M yr −1 to 300 M yr −1 . 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. Results. We find that a significant fraction of galaxies in our sample (29%) experience merging or have close companions that may be gravitationally linked. This places a lower limit on the fraction of interacting galaxies because ongoing mergers are probably also present but harder to identify. We find that at least 44% of the galaxies in our sample display ordered rotation, whereas at least 35% are non-rotating objects. All rotators except one are compatible with rotation-dominated (V max /σ > 1) systems. Non-rotating objects are mainly small objects (R e < 4 kpc). They show an anti-correlation of their velocity dispersion and their effective radius. These lowmass objects (log M star < 10.5) may be ongoing mergers in a transient state, galaxies with only one unresolved star-forming region, galaxies with an unstable gaseous phase or, less probably, spheroids. 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. Conclusions. 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 .

The results obtained from a study of the mass distribution of 36 spiral galaxies are presented. The galaxies were observed using Fabry–Perot interferometry as part of the GHASP survey. The main aim of obtaining high‐resolution Hα 2D velocity fields is to define more accurately the rising part of the rotation curves which should allow to better constrain the parameters of the mass distribution. The Hα velocities were combined with low resolution H i data from the literature, when available. Combining the kinematical data with photometric data, mass models were derived from these rotation curves using two different functional forms for the halo: an isothermal sphere (ISO) and a Navarro–Frenk–White (NFW) profile. For the galaxies already modelled by other authors, the results tend to agree. Our results point at the existence of a constant density core in the centre of the dark matter haloes rather than a cuspy core, whatever the type of the galaxy from Sab to Im. This extends to all types the result already obtained by other authors studying dwarf and low surface brightness galaxies but would necessitate a larger sample of galaxies to conclude more strongly. Whatever model is used (ISO or NFW), small core radius haloes have higher central densities, again for all morphological types. We confirm different halo scaling laws, such as the correlations between the core radius and the central density of the halo with the absolute magnitude of a galaxy: low‐luminosity galaxies have small core radius and high central density. We find that the product of the central density with the core radius of the dark matter halo is nearly constant, whatever the model and whatever the absolute magnitude of the galaxy. This suggests that the halo surface density is independent from the galaxy type.

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.