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We introduce a new set of zoom-in cosmological simulations with sub-pc resolution, intended to model extremely faint, highly magnified star-forming stellar clumps, detected at z=6.14 thanks to gravitational lensing. The simulations include feedback from individual massive stars (in both the pre-supernova and supernova phases), generated via stochastic, direct sampling of the stellar initial mass function. We adopt a modified 'delayed cooling' feedback scheme, specifically created to prevent artificial radiative loss of the energy injected by individual stars in very dense gas (n~10^3-10^5 cm^{-3}). The sites where star formation ignites are characterised by maximum densities of the order of 10^5 cm^{-3} and gravitational pressures P/k>10^7 K/cm^3, corresponding to the values of the local, turbulent regions where the densest stellar aggregates form. The total stellar mass at z=6.14 is 3.4x10^7 M_sun, in satisfactory agreement with the observed stellar mass of the observed systems. The most massive clumps have masses of ~10^6 M_sun and half-mass sizes of ~100 pc. These sizes are larger than the observed ones, including also other samples of lensed high-redshift clumps, and imply an average density one order of magnitude lower than the observed one. In the size-mass plane, our clumps populate a sequence that is intermediate between the ones of observed high-redshift clumps and local dSph galaxies., MNRAS, accepted for publication. 24 pages, 17 figures

We investigate the strongly lensed (\mu x10-100) Lyman continuum (LyC) galaxy, dubbed Sunburst, at z=2.37, taking advantage of a new accurate model of the lens. A characterization of the intrinsic (delensed) properties of the galaxy yields a size of ~3 sq.kpc, a luminosity Muv=-20.3,and a stellar mass M~10^9 Msun;16% of the ultraviolet light is located in a 3 Myr old gravitationally-bound young massive star cluster (YMC) with an effective radius of Re~8 pc and a dynamical mass of ~10^7 Msun (similar to the stellar mass), from which LyC radiation is detected (\lambda < 912A). The inferred outflowing gas velocity (>300 km/s) exceeds the escape velocity of the star cluster. The resulting escape fraction of the ionizing radiation emerging from the Sunburst galaxy is >6-12%, whilst it is >46-93% if inferred from the YMC. 12 additional likely star clusters with 3~30%, which is consistent with the high \Gamma derived in local galaxies experiencing extreme gas physical conditions. The presence of the YMC influences the morphology (nucleation), photometry (photometric jumps) and spectroscopic output (nebular emission) of the entire galaxy. The de-lensed LyC and UV (1600A) magnitudes of the YMC are ~30.6 and ~26.9, whilst the galaxy has m1600~24.8. A relatively large rest-frame equivalent width of EWrest(Hb+[OIII]4959-5007)~450A emerges from the galaxy with the YMC contributing to ~30%. If O-type stars are mainly forged in star clusters, then such engines were the key ionizing agents during reionization and the increasing occurrence of high EW lines (Hb+[OIII]) observed at z>6.5 might be an indirect signature of a high \Gamma at reionization.Future facilities (like VLT/MAVIS or ELT), will probe bound clusters on moderately magnified (\mu, Comment: 17 pages (12 main body), 10 Figures and 1 Table. Accepted for publication in Astronomy & Astrophysics. Figure 6 shows the stellar cluster formation efficiency of the Sunburst galaxy; Figure C.1 shows the MUSE narrow field mode image of the counter-arc

Utilizing spectroscopic observations taken for the VIMOS Ultra-Deep Survey (VUDS), new observations from Keck/DEIMOS, and publicly available observations of large samples of star-forming galaxies, we report here on the relationship between the star formation rate (SFR) and the local environment ($\delta_{gal}$) of galaxies in the early universe ($2, Comment: v2, 24 pages, nine figures, accepted to A&A after minor changes to language and formatting

We study the projected spatial offset between the ultraviolet continuum and Ly$\alpha$ emission for 65 lensed and unlensed galaxies in the Epoch of Reionization ($5\leq z\leq7$), the first such study at these redshifts, in order to understand the potential for these offsets to confuse estimates of the Ly$\alpha$ properties of galaxies observed in slit spectroscopy. While we find that ~40% of galaxies in our sample show significant projected spatial offsets ($|\Delta_{Ly\alpha-UV}|$), we find a modest average offset of 0.61$\pm$0.08 kpc. A small fraction of our sample, ~10%, exhibits offsets of 2-4 kpc, sizes that are larger than the effective radii of typical galaxies at these redshifts. An internal comparison and a comparison to studies at lower redshift yielded no significant evidence of evolution of $|\Delta_{Ly\alpha-UV}|$ with redshift. In our own sample, UV-bright galaxies showed offsets a factor of three greater than their fainter counterparts, 0.89$\pm$0.18 vs. 0.27$\pm$0.05 kpc, respectively. We argue that offsets are likely not the result of merging processes, but are rather due to internal anisotropic processes resulting from stellar feedback facilitates Ly$\alpha$ fluorescence and/or backscattering from nearby or outflowing gas. The reduction in the Ly$\alpha$ flux due to offset effects for various observational setups was quantified through mock observations of simple simulations. It was found that the loss of Ly$\alpha$ photons for galaxies with average offsets is not, if corrected for, a limiting factor for all but the narrowest slit widths (, Comment: 21 pages, 7 figures, 2 tables. Updated with the accepted MNRAS version that includes minor changes to the text and two tables

The identification of young massive star clusters (YMCs) at high redshift is becoming a real fact. We present recent results from Hubble deep imaging and VLT/ MUSE - X-Shooter observations boosted by strong gravitational lensing. We report on two parsec-scale star-forming systems at z = 6.145 and 2.37 (>10 Gyrs of look back time) currently representing the best candidate high-z YMCs. All of this also implies that the search for globular cluster precursors has already begun.

To identify the galaxies responsible for the reionization of the Universe, we must rely on the investigation of the Lyman Continuum (LyC) properties of z70{\AA}, Lya(ext)70{\AA}), have much higher LyC fluxes compared to the rest of the galaxy population in agreement with theoretical studies and previous observational works. We also find that galaxies with low Lya(ext) have the highest LyC flux: this new correlation seems even stronger than the correlations with high EWLya and small rUV. These results assume that the stacks from all the subsamples present the same statistical contamination from lower redshift interlopers. If we subtract a statistical contamination from low redshift interlopers obtained with dedicated Monte Carlo simulations, from the flux density ratios (fnu(895)/fnu(1470)) of the significant subsamples we find that these samples contain real LyC leaking flux with a very high probability, but the true average escape fractions remain uncertain. Our work indicates that galaxies with very high EWLya, small Lya(ext) and small rUV are very likely the best candidates to show LyC radiation at z=4 and could therefore be the galaxies that contributed more to reionization., Comment: Accepted by A&A

Many cosmological studies predict that early supermassive black holes (SMBHs) can only form in the most massive dark matter halos embedded within large scale structures marked by galaxy over-densities that may extend up to 10 physical Mpc. This scenario, however, has not been confirmed observationally, as the search for galaxy over-densities around high-z quasars has returned conflicting results. The field around the z=6.28 quasar SDSSJ1030+0524 (J1030) is unique for multi-band coverage and represents an excellent data legacy for studying the environment around a primordial SMBH. In this paper we present wide-area (25x25 arcmin), Y- and J-band imaging of the J1030 field obtained with the near infrared camera WIRCam at the Canada-France-Hawaii Telescope (CFHT). We built source catalogues in the Y- and J-band, and matched those with our photometric catalogue in the r, z, i bands presented in Morselli et al. (2014). We used these new infrared data together with H and K and Spitzer/IRAC data to refine our selection of Lyman Break Galaxies (LBGs), extending our selection criteria to galaxies in the range 25.2=1.3. We found a significant asymmetry in the distribution of the high-z galaxies in J1030, supporting the existence of a coherent large-scale structure around the quasar. We compared our results with those of Bowler et al. (2015), who adopted similar LBGs selection criteria, and estimated an over-density of galaxies in the field of delta = 2.4, which is significant at >4 sigma. The over-density value and its significance are higher than those found in Morselli et al. (2014), and we interpret this as evidence of an improved LBG selection., Comment: 13 pages, 8 figures, accepted for publication in A&A

This paper describes the first data release (DR1) of the VIMOS Ultra Deep Survey (VUDS). The DR1 includes all low-resolution spectroscopic data obtained in 276.9 arcmin2 of the CANDELS-COSMOS and CANDELS-ECFDS survey areas, including accurate spectroscopic redshifts z_spec and individual spectra obtained with VIMOS on the ESO-VLT. A total of 698 objects have a measured redshift, with 677 galaxies, two type-I AGN and a small number of 19 contaminating stars. The targets of the spectroscopic survey are selected primarily on the basis of their photometric redshifts to ensure a broad population coverage. About 500 galaxies have z_spec>2, 48 with z_spec>4, and the highest reliable redshifts reach beyond z_spec=6. This dataset approximately doubles the number of galaxies with spectroscopic redshifts at z>3 in these fields. We discuss the general properties of the sample in terms of the spectroscopic redshift distribution, the distribution of Lyman-alpha equivalent widths, and physical properties including stellar masses M_star and star formation rates (SFR) derived from spectral energy distribution fitting with the knowledge of z_spec. We highlight the properties of the most massive star-forming galaxies, noting the large range in spectral properties, with Lyman-alpha in emission or in absorption, and in imaging properties with compact, multi-component or pair morphologies. We present the catalogue database and data products. All data are publicly available and can be retrieved from a dedicated query-based database available at http://cesam.lam.fr/vuds., 11 pages, 6 figures, submitted to A&A

The reionization of the Universe is one of the most important topics of present day astrophysical research. The most plausible candidates for the reionization process are star-forming galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the HI ionizing background at z~3. We aim at measuring the Lyman continuum escape fraction, which is one of the key parameters to compute the contribution of star-forming galaxies to the UV background. We have used ultra-deep U-band imaging (U=30.2mag at 1sigma) by LBC/LBT in the CANDELS/GOODS-North field, as well as deep imaging in COSMOS and EGS fields, in order to estimate the Lyman continuum escape fraction of 69 star-forming galaxies with secure spectroscopic redshifts at 3.27L*), while for the faint population (L=0.2L*) the limit to the escape fraction is ~10%. We have computed the contribution of star-forming galaxies to the observed UV background at z~3 and we have found that it is not enough to keep the Universe ionized at these redshifts, unless their escape fraction increases significantly (>10%) at low luminosities (M1500>-19). We compare our results on the Lyman continuum escape fraction of high-z galaxies with recent estimates in the literature and discuss future prospects to shed light on the end of the Dark Ages. In the future, strong gravitational lensing will be fundamental to measure the Lyman continuum escape fraction down to faint magnitudes (M1500~-16) which are inaccessible with the present instrumentation on blank fields., Comment: Accepted for publication in A&A, 16 pages, 6 figures

We constrain the evolution of the galaxy mass and luminosity functions from the analysis of (public) multi-wavelength data in the Chandra Deep Field South (CDFS) area, obtained from the GOODS and other projects, and including very deep high-resolution imaging by HST/ACS. Our reference catalogue of faint high-redshift galaxies, which we have thoroughly tested for completeness and reliability, comes from a deep (S(3.6micron)>1 microJy) image by IRAC on the Spitzer Observatory. These imaging data in the field are complemented with extensive optical spectroscopy by the ESO VLT/FORS2 and VIMOS spectrographs, while deep K-band VLT/ISAAC imaging is also used to derive further complementary statistical constraints and to assist the source identification and SED analysis. We have selected a highly reliable IRAC 3.6micron sub-sample of 1478 galaxies with S(3.6)>10microJy, 47% of which have spectroscopic redshift, while for the remaining objects both COMBO-17 and Hyperz are used to estimate the photometric redshift. This very extensive dataset is exploited to assess evolutionary effects in the galaxy luminosity and stellar mass functions, while luminosity/density evolution is further constrained with the number counts and redshift distributions. The deep ACS imaging allows us to differentiate these evolutionary paths by morphological type, which our simulations show to be reliable at least up to z=1.5 for the two main early- (E/S0) and late-type (Sp/Irr) classes. These data, as well as our direct estimate of the stellar mass function above M=10^(10)M_sun for the spheroidal subclass, consistently evidence a progressive dearth of such objects to occur starting at z=0.7, paralleled by an increase in luminosity. (abridged), paper accepted for publication in A&A

[abr] We report the analysis of three galaxies selected in the Hubble Deep Field South at Ks 3. We have used population synthesis models to constrain their redshifts and their stellar masses. One galaxy is at redshift z_p~2.4 while the other two are at z_p~2.9-3.0. All three galaxies have already assembled a stellar mass of about 10^{11} M_sun at the observed redshift placing the possible merging event of their formation at z>3.5. The inferred mass weighted age of their stellar populations implies that the bulk of the stars formed at z_f>3.5. The resulting co-moving density of M_{stars}>10^{11} M_sun galaxies at ~2.7 is rho=1.2(+-0.7)x10^{-4} Mpc^{-3}, about a factor two higher than the predictions of hierarchical models. The comparison with the local density of galaxies implies that the three galaxies must have already formed most of their stellar mass and that they cannot follow an evolution significantly different from a passive aging.The comparison with the density of local L>L* early types (passively evolved galaxies) suggests that their co-moving density cannot decrease by more than a factor 2.5-3 from z=0 to z~3 and that up to 40% of the stellar mass content of bright (L>L*) local early type galaxies was already in place at z>2.5.

We present the VIMOS Ultra Deep Survey (VUDS), a spectroscopic redshift survey of ~10.000 very faint galaxies to study the major phase of galaxy assembly 2, Comment: 43 pages, 30 figures, submitted to A&A

Aims. Cosmic reionization is an important process occurring in the early epochs of the Universe. However, because of observational limitations due to the opacity of the intergalactic medium to Lyman continuum photons, the nature of ionizing sources is still not well constrained. While high-redshift star-forming galaxies are thought to be the main contributors to the ionizing background at z > 6, it is impossible to directly detect their ionizing emission. Therefore, looking at intermediate redshift analogues (z ∼ 2?4) can provide useful hints about cosmic reionization. Methods. We investigate the physical properties of one of the best Lyman continuum emitter candidate at z = 3.212 found in the GOODS-S/CANDELS field with photometric coverage from the U to the MIPS 24 ?m band and VIMOS/VLT and MOSFIRE/Keck spectroscopy. These observations allow us to derive physical properties such as stellar mass, star formation rate, age of the stellar population, dust attenuation, metallicity, and ionization parameter, and to determine how these parameters are related to the Lyman continuum emission. Results. Investigation of the UV spectrum confirms a direct spectroscopic detection of the Lyman continuum emission with S/N > 5. Non-zero Lyaα flux at the systemic redshift and high Lyman-aα ESCape fraction (f(Lyaα) ≥ 0.78) suggest a low H i column density. The weak C and Si low-ionization absorption lines are also consistent with a low covering fraction along the line of sight. The subsolar abundances are consistent with a young and extreme starburst. The [O iii] iiiλλ4959, 5007+Hβ equivalent width (EW) is one of the largest reported for a galaxy at z > 3 (EW([O iii] λλ4959, 5007 + Hβ) ≈1600 Å, rest-frame; 6700 Å observed-frame) and the near-infrared spectrum shows that this is mainly due to an extremely strong [O iii] emission. The large observed [O iii]/[O ii] ratio (>10) and high ionization parameter are consistent with prediction from photoionization models in the case of a density-bounded nebula scenario. Furthermore, the EW([O iiiλλ4959, 5007+Hβ) is comparable to recent measurements reported at z ∼ 7?9, in the reionization epoch. We also investigate the possibility of an AGN contribution to explain the ionizing emission but most of the AGN identification diagnostics suggest that stellar emission dominates instead. Conclusions. This source is currently the first high-z example of a Lyman continuum emitter exhibiting indirect and direct evidences of a Lyman continuum leakage and having physical properties consistent with theoretical expectation from Lyman continuum emission from a density-bounded nebula. A low H i column density, low covering fraction, compact star formation activity, and a possible interaction/merging of two systems may contribute to the Lyman continuum photon leakage. © 2015 ESO., We acknowledge the financial contribution from PRIN-INAF 2012.

The relation between the galaxy stellar mass M_star and the dark matter halo mass M_h gives important information on the efficiency in forming stars and assembling stellar mass in galaxies. We present the stellar mass to halo mass ratio (SMHR) measurements at redshifts 2, Comment: 4 pages, 2 figures, submitted to A&A

We present VIMOS-VLT spectroscopy of the Frontier Fields cluster MACS~J0416.1-2403 (z=0.397). Taken as part of the CLASH-VLT survey, the large spectroscopic campaign provided more than 4000 reliable redshifts, including ~800 cluster member galaxies. The unprecedented sample of cluster members at this redshift allows us to perform a highly detailed dynamical and structural analysis of the cluster out to ~2.2$r_{200}$ (~4Mpc). Our analysis of substructures reveals a complex system composed of a main massive cluster ($M_{200}$~0.9$\times 10^{15} M_{\odot}$) presenting two major features: i) a bimodal velocity distribution, showing two central peaks separated by $\Delta V_{rf}$~1100 km s$^{-1}$ with comparable galaxy content and velocity dispersion, ii) a projected elongation of the main substructures along the NE-SW direction, with a prominent subclump ~600 kpc SW of the center and an isolated BCG approximately halfway between the center and the SW clump. We also detect a low mass structure at z~0.390, ~10' S of the cluster center, projected at ~3Mpc, with a relative line-of-sight velocity of $\Delta V_{rf}$~-1700 km s$^{-1}$. The cluster mass profile that we obtain through our dynamical analysis deviates significantly from the "universal" NFW, being best fit by a Softened Isothermal Sphere model instead. The mass profile measured from the galaxy dynamics is found to be in relatively good agreement with those obtained from strong and weak lensing, as well as with that from the X-rays, despite the clearly unrelaxed nature of the cluster. Our results reveal overall a complex dynamical state of this massive cluster and support the hypothesis that the two main subclusters are being observed in a pre-collisional phase, in line with recent findings from radio and deep X-ray data. With this article we also release the entire redshift catalog of 4386 sources in the field of this cluster., Comment: Accepted for publication on ApJS. Revised to match the accepted version; 21 pages, 18 figures, 9 tables. The CLASH-VLT spectroscopic catalogs are publicly available at: http://sites.google.com/site/vltclashpublic/

MOONS is a new Multi-Object Optical and Near-infrared Spectrograph selected by ESO as a third generation instrument for the Very Large Telescope (VLT). The grasp of the large collecting area offered by the VLT (8.2m diameter), combined with the large multiplex and wavelength coverage (optical to near-IR: 0.8μm - 1.8μm) of MOONS will provide the European astronomical community with a powerful, unique instrument able to pioneer a wide range of Galactic, Extragalactic and Cosmological studies and provide crucial follow-up for major facilities such as Gaia, VISTA, Euclid and LSST. MOONS has the observational power needed to unveil galaxy formation and evolution over the entire history of the Universe, from stars in our Milky Way, through the redshift desert, and up to the epoch of very first galaxies and re-ionization of the Universe at redshift z>8-9, just few million years after the Big Bang. On a timescale of 5 years of observations, MOONS will provide high quality spectra for >3M stars in our Galaxy and the local group, and for 1-2M galaxies at z>1 (SDSS-like survey), promising to revolutionise our understanding of the Universe. The baseline design consists of ~1000 fibers deployable over a field of view of ~500 square arcmin, the largest patrol field offered by the Nasmyth focus at the VLT. The total wavelength coverage is 0.8μm-1.8μm and two resolution modes: medium resolution and high resolution. In the medium resolution mode (R~4,000-6,000) the entire wavelength range 0.8μm-1.8μm is observed simultaneously, while the high resolution mode covers simultaneously three selected spectral regions: one around the CaII triplet (at R~8,000) to measure radial velocities, and two regions at R~20,000 one in the J-band and one in the H-band, for detailed measurements of chemical abundances. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

We use ultra-deep ultraviolet VLT/VIMOS intermediate-band and VLT/FORS1 narrow-band imaging in the GOODS Southern field to derive limits on the distribution of the escape fraction (f_esc) of ionizing radiation for L >~ L*(z=3) Lyman Break Galaxies (LBGs) at redshift 3.4--4.5. Only one LBG, at redshift z=3.795, is detected in its Lyman continuum (LyC; S/N~5.5), the highest redshift galaxy currently known with a direct detection. Its ultraviolet morphology is quite compact (R_eff=0.8, kpc physical). Three out of seven AGN are also detected in their LyC, including one at redshift z=3.951 and z850 = 26.1. From stacked data (LBGs) we set an upper limit to the average f_esc in the range 5%--20%, depending on the how the data are selected (e.g., by magnitude and/or redshift). We undertake extensive Monte Carlo simulations that take into account intergalactic attenuation, stellar population synthesis models, dust extinction and photometric noise in order to explore the moments of the distribution of the escaping radiation. Various distributions (exponential, log-normal and Gaussian) are explored. We find that the median f_esc is lower than ~6% with an 84% percentile limit not larger than 20%. If this result remains valid for fainter LBGs down to current observational limits, then the LBG population might be not sufficient to account for the entire photoionization budget at the redshifts considered here, with the exact details dependent upon the assumed ionizing background and QSO contribution thereto. It is possible that f_esc depends on the UV luminosity of the galaxies, with fainter galaxies having higher f_esc, and estimates of f_esc from a sample of faint LBG from the HUDF (i775, Comment: 58 pages, 23 figures; submitted to ApJ, revised version in response to referee's comments

We investigate the possibility of contamination by lower-redshift interlopers in the measure of the ionising radiation escaping from high redshift galaxies. Taking advantage of the new ultra-deep VLT/VIMOS U-band number counts in the GOODS-S field,we calculate the expected probability of contamination by low-z interlopers as a function of the U-mag and the image spatial resolution (PSF). Assuming that ground-based observations can not resolve objects lying within a 0.5" radius of each other, then each z>=3 galaxy has a 2.1 and 3.2% chance of foreground contamination, adopting surface density U-band number counts down to 27.5 and 28.5,respectively. Those probabilities increase to 8.5 and 12.6%, assuming 1.0" radius. If applied to the estimates reported in the literature at z~3 for which a Lyman continuum has been observed directly,the probability that at least 1/3 of them are affected by foreground contamination is larger than 50%.From a Monte-Carlo simulation we estimate the median integrated contribution of foreground sources to the Lyman continuum flux (f900). Current estimations from stacked data are >2 sigma of the median integrated pollution by foreground sources.The spatial cross-correlation between the U-band catalog and a sample of galaxies at z>=3.4 in the GOODS-S field,produces a number of U-band detected systems fully consistent with the expected superposition statistics. Indeed, each of them shows the presence of at least one offset contaminant in the ACS images. An exemplary case of a foreground contamination in the HUDF at redshift 3.797 by a foreground blue compact source (U=28.63 +/- 0.2) is reported; if observed with a seeing larger than 0.5" the polluting source would mimic an observed (f1500/f900)_OBS ~ 38, erroneously ascribed to the source at higher redshift. [Abridged]

We report on observations of Lyman-break galaxies (LBGs) selected from the Great Observatories Origins Deep Survey at mean redshift z~4, 5 and 6, obtained with FORS2 spectrograph at the ESO-VLT.This program has yielded spectroscopic identifications for 114 galaxies of which 51 are at z~4, 31 at z~5, and 32 at z~6. The adopted selection criteria are effective, identifying galaxies at the expected redshift with minimal foreground contamination. Once selection effects are properly accounted for, the rest-frame UV spectra of the higher-redshift LBGs appear to be similar to their counterparts at z~3. As at z~3, LBGs at z~4 and z~5 show Lya both in emission and in absorption; when in absorption, strong interstellar lines and red UV spectra are observed, a fact also measured at z~2 and 3. At z~6, sensitivity issues bias our sample towards galaxies with Lya in emission; nevertheless, these spectra appear to be similar to their lower-redshift counterparts. As in other studies at similar redshifts, we find clear evidence that brighter LBGs tend to have weaker Lya emission lines. At fixed rest-frame UV luminosity, the equivalent width of the Lya emission line is larger at higher redshifts. At all redshifts where the measurements can be reliably made, the redshift of the Lya emission line turns out to be larger than that of the interstellar absorption lines,with a median velocity difference DeltaV~400 km/s at z~4 and 5, consistent with results at lower redshifts. This shows that powerful, large-scale winds are common at high redshift.In general,there is no strong correlation between the morphology of the UV light and the spectroscopic properties. However, galaxies with deep interstellar absorption lines and strong Lya absorption appear to be more diffuse than galaxies with Lya in emission.(abridged), 58 pages, 19 figures, accepted for publication in The Astrophysical Journal

We investigate the properties of a clump-cluster galaxy at redshift 1.57. The morphology of this galaxy is dominated by eight star-forming clumps in optical observations, and has photometric properties typical of most clump-cluster and chain galaxies. Its complex asymmetrical morphology has led to the suggestion that this system is a group merger of several initially separate proto-galaxies. We performed H_alpha integral field spectroscopy of this system using SINFONI on VLT UT4. These observations reveal a large-scale velocity gradient throughout the system, but with large local kinematic disturbances. Using a numerical model of gas-rich disk fragmentation, we find that clump interactions and migration can account for the observed disturbed rotation. On the other hand, the global rotation would not be expected for a multiply merging system. We further find that this system follows the stellar mass vs. metallicity, star formation rate and size relations expected for a disk at this redshift, and exhibits a disk-like radial metallicity gradient, so that the scenario of internal disk fragmentation is the most likely one. A red and metallic central concentration appears to be a bulge in this proto-spiral clumpy galaxy. A chain galaxy at redshift 2.07 in the same field also shows disk-like rotation. Such systems are likely progenitors of the present-day bright spiral galaxies, forming their exponential disks through clump migration and disruption and fueling their bulges. Our present results show that disturbed morphologies and kinematics are not necessarily signs of galaxy mergers and interactions, and can instead result from the internal evolution of primordial disks., A&A, accepted. Version with full resolution figures available at http://aramis.obspm.fr/~bournaud/udfr2.pdf -- Animation of clumpy galaxy models available at http://aramis.obspm.fr/~bournaud/cc/cc.html

[Abridged] We present the rest-frame Js-band and Ks-band luminosity function of a sample of about 300 galaxies selected in the HDF-S at Ks0.8 suggests that a significant fraction of them increases their stellar mass at 13. Thus, our results suggest that the assembly of high-mass galaxies is spread over a large redshift range and that the increase of their stellar mass has been very efficient also at very high redshift at least for a fraction of them., Comment: 18 pages, 21 figures, Accepted for publication in MNRAS

More than half of all stars in the local Universe are found in massive spheroidal galaxies, which are characterized by old stellar populations with little or no current star formation. In present models, such galaxies appear rather late as the culmination of a hierarchical merging process, in which larger galaxies are assembled through mergers of smaller precursor galaxies. But observations have not yet established how, or even when, the massive spheroidals formed, nor if their seemingly sudden appearance when the Universe was about half its present age (at redshift z \approx 1) results from a real evolutionary effect (such as a peak of mergers) or from the observational difficulty of identifying them at earlier epochs. Here we report the spectroscopic and morphological identification of four old, fully assembled, massive (>10^{11} solar masses) spheroidal galaxies at 1.6, Comment: Nature, in press as a Letter, 8th July issue. 12 pages, 1 Table, 4 Figures

An analysis of the galaxy evolution from deep multicolor imaging of optically and infrared selected galaxies is presented and compared with current models of galaxy formation and evolution. A very deep K=20-23) sample of optically and infrared selected galaxies from ESO/VLT and HST surveys like the HDF South, Chandra Deep Field, NTT Deep Field is being analyzed. First results are shown in terms of the high redshift rest frame UV luminosity density and rest frame blue luminosity function and compared with predictions of CDM hierarchical models for galaxy formation and evolution. The observations show an excess of bright sources at very high redshifts 5 z

We present an estimate of the cosmological evolution of the field galaxy luminosity function (LF) in the rest frame 4400 Angstrom B -band up to redshift z=3.5. To this purpose, we use a composite sample of 1541 I--selected galaxies selected down to I_(AB)=27.2 and 138 galaxies selected down to K_(AB)=25 from ground-based and HST multicolor surveys, most notably the new deep JHK images in the Hubble Deep Field South (HDF-S) taken with the ISAAC instrument at the ESO-VLT telescope. About 21% of the sample has spectroscopic redshifts, and the remaining fraction well calibrated photometric redshifts. The resulting blue LF shows little density evolution at the faint end with respect to the local values, while at the bright end (M_B(AB), Comment: 14 pages, 2 figures, Astrophysical Journal Letters, in press

We present a sample of 17 high-redshift (3.5

THESEUS is a space mission concept aimed at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. These goals will be achieved through a unique combination of instruments allowing GRBs and X-ray transients detection over a broad FOV (more than 1sr) with 0.5-1 arcmin localization, an energy band extending from several MeVs down to 0.3 keV and high sensitivity to transient sources in the soft X-ray domain, as well as on-board prompt (few minutes) follow-up with a 0.7 m class IR telescope with both imaging and spectroscopic capabilities. THESEUS will be perfectly suited for addressing the main open issues in cosmology such as, e.g., star formation rate and metallicity evolution of the inter-stellar and intra-galactic medium up to redshift ∼10, signatures of Pop III stars, sources and physics of re-ionization, and the faint end of the galaxy luminosity function. In addition, it will provide unprecedented capability to monitor the X-ray variable sky, thus detecting, localizing, and identifying the electromagnetic counterparts to sources of gravitational radiation, which may be routinely detected in the late '20s / early '30s by next generation facilities like aLIGO/ aVirgo, eLISA, KAGRA, and Einstein Telescope. THESEUS will also provide powerful synergies with the next generation of multi-wavelength observatories (e.g., LSST, ELT, SKA, CTA, ATHENA).