Aims. The centre of the Milky Way is the nearest nucleus of a galaxy and offers a unique possibility to study the structure and dynamics of a dense stellar cluster around a super-massive black hole. Methods. We present high-resolution seeing limited and AO NIR imaging observations of the stellar cluster within about one parsec of Sgr A*, the massive black hole at the centre of the Milky Way. Stellar number counts and the diffuse background light density were extracted from these observations in order to examine the structure of the nuclear stellar cluster. A detailed map of the variation of interstellar extinction in the central ∼0.5 pc of the Milky Way is presented and used to correct the stellar number counts and diffuse light density. Results. Our findings are as follows: (a) a broken-power law provides an excellent fit to the overall structure of the GC nuclear cluster. The power-law slope of the cusp is Γ = 0.19 ± 0.05, the break radius is R break = 6.0 ± 1.0 or 0.22 ± 0.04 pc, and the cluster density decreases with a power-law index of Γ = 0.75 ± 0.1 outside of R break . (b) Using the best velocity dispersion measurements from the literature, we derive higher mass estimates for the central parsec than assumed until now. The inferred density of the cluster at the break radius is 2.8 ± 1.3 × 10 6 M pc −3 . This high density agrees well with the small extent and flat slope of the cusp. Possibly, the mass of the stars makes up only about 50% of the total cluster mass. (c) Possible indications of mass segregation in the cusp are found (d) The cluster appears not entirely homogeneous. Several density clumps are detected that are concentrated at projected distances of R = 3 and R = 7 from Sgr A*. (e) There appears to exist an under-density of horizontal branch/red clump stars near R = 5 , or an over-density of stars of similar brightness at R = 3 and R = 7 . (f) The extinction map in combination with cometary-like features in an L -band image may provide support for the assumption of an outflow from Sgr A*.

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 ELODIE archive contains the complete collection of high-resolution echelle spectra accumulated over the last decade using the ELODIE spectrograph at the Observatoire de Haute-Provence 1.93-m telescope. This article presents the different data products and the facilities available on the web to re-process these data on-the-fly. Users can retrieve the data in FITS format from http://atlas.obs-hp.fr/elodie and apply to them different functions: wavelength resampling and flux calibration in particular.

Aims. The estimate of radial abundance gradients in high-redshift galaxies allows to constrain their star formation history and their interplay with the surrounding intergalactic medium. Methods. We present VLT/SINFONI integral-field spectroscopy of a first sample of 50 galaxies at z ∼ 1.2 in the MASSIV survey. Using the N2 ratio between the [N ii]6584 and Hα rest-frame optical emission lines as a proxy for oxygen abundance in the interstellar medium, we measured the metallicity of the sample galaxies. We developed a tool to extract spectra in annular regions, leading to a spatially resolved estimate of the oxygen abundance in each galaxy. We were able to derive a metallicity gradient for 26 galaxies in our sample and discovered a significant fraction of galaxies with a "positive" gradient. Using a simple chemical evolution model, we derived infall rates of pristine gas onto the disks. Results. Seven galaxies display a positive gradient at a high confidence level. Four out of these are interacting, and one is a chain galaxy. We suggest that interactions might be responsible for shallowing and even inverting the abundance gradient. We also identify two interesting correlations in our sample: a) galaxies with higher gas velocity dispersion have shallower/positive gradients; and b) metal-poor galaxies tend to show a positive gradient, whereas metal-rich ones tend to show a negative one. This last observation can be explained by the infall of metal-poor gas into the center of the disks. We address the question of the origin of this infall under the influence of gas flows triggered by interactions and/or cold gas accretion. All the data published in this paper are publicly available at the time of publication following this link: http://cosmosdb.lambrate.inaf.it/VVDS-SINFONI.