Search

Aims. We wish to investigate the physical properties of a sample of Lyα emitting galaxies in the VANDELS survey, with particular focus on the role of kinematics and neutral hydrogen column density in the escape and spatial distribution of Lyα photons. Methods. From all the Lyα emitting galaxies in the VANDELS Data Release 2 at 3.5 ≲ z ≲ 4.5, we selected a sample of 52 galaxies that also have a precise systemic redshift determination from at least one nebular emission line (HeII or CIII]). For these galaxies, we derived different physical properties (stellar mass, age, dust extinction, and star formation rate) from spectral energy distribution (SED) fitting of the exquisite multiwavelength photometry available in the VANDELS fields, using the dedicated spectral modeling tool BEAGLE and the UV β slope from the observed photometry. We characterized the Lyα emission in terms of kinematics, equivalent width (EW), full width at half-maximum, and spatial extension and then estimated the velocity of the neutral outflowing gas. The ultra-deep VANDELS spectra (up to 80 h on-source integration) enable this for individual galaxies without the need to rely on stacks. We then investigated the correlations between the Lyα properties and the other measured properties to study how they affect the shape and intensity of Lyα emission. Results. We reproduce some of the well-known correlations between Lyα EW and stellar mass, dust extinction, and UV β slope, in the sense that the emission line appears brighter in galaxies with lower mass that are less dusty and bluer. We do not find any correlation with the SED-derived star formation rate, while we find that galaxies with brighter Lyα tend to be more compact in both UV and in Lyα. Our data reveal an interesting correlation between the Lyα velocity offset and the shift of the interstellar absorption lines with respect to the systemic redshift, observed for the first time at high redshifts: galaxies with higher interstellar medium (ISM) outflow velocities show smaller Lyα velocity shifts. We interpret this relation in the context of the shell-model scenario, where the velocity of the ISM and the HI column density contribute together in determining the Lyα kinematics. In support to our interpretation, we observe that galaxies with high HI column densities have much more extended Lyα spatial profiles; this is a sign of increased scattering. However, we do not find any evidence that the HI column density is related to any other physical properties of the galaxies, although this might be due in part to the limited range of parameters that our sample spans. [ABSTRACT FROM AUTHOR]

We unveil the complex shape of a proto-supercluster at z ∼ 2.45 in the COSMOS field exploiting the synergy of both spectroscopic and photometric redshifts. Thanks to the spectroscopic redshifts of the VIMOS Ultra-Deep Survey (VUDS), complemented by the zCOSMOS-Deep spectroscopic sample and high-quality photometric redshifts, we compute the three-dimensional (3D) overdensity field in a volume of ∼100 × 100 × 250 comoving Mpc3 in the central region of the COSMOS field, centred at z ∼ 2.45 along the line of sight. The method relies on a two-dimensional (2D) Voronoi tessellation in overlapping redshift slices that is converted into a 3D density field, where the galaxy distribution in each slice is constructed using a statistical treatment of both spectroscopic and photometric redshifts. In this volume, we identify a proto-supercluster, dubbed "Hyperion" for its immense size and mass, which extends over a volume of ∼60 × 60 × 150 comoving Mpc3 and has an estimated total mass of ∼4.8 × 1015M⊙. This immensely complex structure contains at least seven density peaks within 2.4 ≲ z ≲ 2.5 connected by filaments that exceed the average density of the volume. We estimate the total mass of the individual peaks, Mtot, based on their inferred average matter density, and find a range of masses from ∼0.1 × 1014M⊙ to ∼2.7 × 1014M⊙. By using spectroscopic members of each peak, we obtain the velocity dispersion of the galaxies in the peaks, and then their virial mass Mvir (under the strong assumption that they are virialised). The agreement between Mvir and Mtot is surprisingly good, at less than 1−2σ, considering that (almost all) the peaks are probably not yet virialised. According to the spherical collapse model, these peaks have already started or are about to start collapsing, and they are all predicted to be virialised by redshift z ∼ 0.8−1.6. We finally perform a careful comparison with the literature, given that smaller components of this proto-supercluster had previously been identified using either heterogeneous galaxy samples (Lyα emitters, sub-mm starbursting galaxies, CO emitting galaxies) or 3D Lyα forest tomography on a smaller area. With VUDS, we obtain, for the first time across the central ∼1 deg2 of the COSMOS field, a panoramic view of this large structure, that encompasses, connects, and considerably expands in a homogeneous way on all previous detections of the various sub-components. The characteristics of this exceptional proto-supercluster, its redshift, its richness over a large volume, the clear detection of its sub-components, together with the extensive multi-wavelength imaging and spectroscopy granted by the COSMOS field, provide us the unique possibility to study a rich supercluster in formation. [ABSTRACT FROM AUTHOR]

Context. To identify the galaxies responsible for the reionization of the Universe, we must rely on the investigation of the Lyman continuum (LyC) properties of z ≲ 5 star-forming galaxies, where we can still directly observe their ionizing radiation. Aims. The aim of this work is to explore the correlation between the LyC emission and some of the proposed indirect indicators of LyC radiation at z ~ 4 such as a bright Lyα emission and a compact UV continuum size. Methods. We selected a sample of 201 star-forming galaxies from the Vimos Ultra Deep Survey (VUDS) at 3.5 ≤ z ≤ 4.3 in the COSMOS, ECDFS, and VVDS-2h fields, including only those with reliable spectroscopic redshifts, a clean spectrum in the LyC range and clearly not contaminated by bright nearby sources in the same slit. For all galaxies we measured the Lyα EW, the Lyα velocity shift with respect to the systemic redshift, the Lyα spatial extension and the UV continuum effective radius. We then selected different sub-samples according to the properties predicted to be good LyC emission indicators: in particular we created sub-samples of galaxies with EW(Lyα) ≥ 70 Å, Lyαext ≤ 5.7 kpc, rUV ≤ 0.30 kpc and |ΔvLyα|≤ 200 km s−1. We stacked all the galaxies in each sub-sample and measured the flux density ratio (fλ(895)∕fλ(1470)), that we considered to be a proxy for LyC emission. We then compared these ratios to those obtained for the complementary samples. Finally, to estimate the statistical contamination from lower redshift inter-lopers in our samples, we performed dedicated Monte Carlo simulations using an ultradeep U-band image of the ECDFS field. Results. We find that the stacks of galaxies which are UV compact (rUV ≤ 0.30 kpc) and have bright Lyα emission (EW(Lyα) ≥ 70 Å), have much higher LyC fluxes compared to the rest of the galaxy population. These parameters appear to be good indicators of LyC radiation in agreement with theoretical studies and previous observational works. In addition we find that galaxies with a low Lyα spatial extent (Lyαext ≤ 5.7 kpc) have higher LyC flux compared to the rest of the population. Such a correlation had never been analysed before and seems even stronger than the correlation with high EW(Lyα) and small rUV. These results assume that the stacks from all sub-samples present the same statistical contamination from lower redshift interlopers. If we subtract a statistical contamination from low redshift interlopers obtained with the simulations from the flux density ratios (fλ(895)∕fλ(1470)) of the significant sub-samples we find that these samples contain real LyC leaking flux with a very high probability, although the true average escape fractions are very uncertain. Conclusions. Our work indicates that galaxies with very high EW(Lyα), small Ly αext and small rUV are very likely the best candidates to show Lyman continuum radiation at z ~ 4 and could therefore be the galaxies that have contributed most to reionisation. [ABSTRACT FROM AUTHOR]

In this paper we aim at improving constraints on the epoch of galaxy formation by measuring the ages of 3597 galaxies with reliable spectroscopic redshifts 2 ≤ z ≤ 6:5 in the VIMOS Ultra Deep Survey (VUDS). We derive ages and other physical parameters from the simultaneous fitting with the GOSSIP+ software of observed UV rest-frame spectra and photometric data from the u band up to 4.5 μm using model spectra from composite stellar populations. We perform extensive simulations and conclude that at z ≥ 2 the joint analysis of spectroscopy and photometry, combined with restricted age possibilities when taking the age of the Universe into account, substantially reduces systematic uncertainties and degeneracies in the age derivation; we find that age measurements from this process are reliable. We find that galaxy ages range from very young with a few tens of million years to substantially evolved with ages up to 1.5 Gyr or more. This large age spread is similar for different age definitions including ages corresponding to the last major star formation event, stellar mass-weighted ages, and ages corresponding to the time since the formation of 25% of the stellar mass. We derive the formation redshift zf from the measured ages and find galaxies that may have started forming stars as early as zf ~ 15. We produce the formation redshift function (FzF), the number of galaxies per unit volume formed at a redshift zf, and compare the FzF in increasing observed redshift bins finding a remarkably constant FzF. The FzF is parametrized with (1 + z)ζ, where ζ ≃ 0:58 ± 0:06, indicating a smooth increase of about 2 dex from the earliest redshifts, z ~ 15; to the lowest redshifts of our sample at z ~ 2. Remarkably, this observed increase in the number of forming galaxies is of the same order as the observed rise in the star formation rate density (SFRD). The ratio of the comoving SFRD with the FzF gives an average SFR per galaxy of ~7-17 M⊙=yr at z ~ 4-6, in agreement with the measured SFR for galaxies at these redshifts. From the smooth rise in the FzF we infer that the period of galaxy formation extends all the way from the highest possible formation redshifts that we can probe at z ~ 15 down to redshifts z ~ 2. This indicates that galaxy formation is a continuous process over cosmic time, with a higher number of galaxies forming at the peak in SFRD at z ~ 2 than at earlier epochs. [ABSTRACT FROM AUTHOR]

Context: Determining the average fraction of Lyman continuum (LyC) photons escaping high redshift galaxies is essential for understanding how reionization proceeded in the z> 6 Universe. Aims: We want to measure the LyC signal from a sample of sources in the Chandra Deep Field South (CDFS) and COSMOS fields for which ultra-deep VIMOS spectroscopy as well as multi-wavelength Hubble Space Telescope (HST) imaging are available. Methods: We select a sample of 46 galaxies at z ~ 4 from the VIMOS Ultra Deep Survey (VUDS) database, such that the VUDS spectra contain the LyC part, that is, the rest-frame range 880-910 Å. Taking advantage of the HST imaging, we apply a careful cleaning procedure and reject all the sources showing nearby clumps with different colours, that could potentially be lower-redshift interlopers. After this procedure, the sample is reduced to 33 galaxies. We measure the ratio between ionizing flux (LyC at 895 Å) and non-ionizing emission (at ~ 1500 Å) for all individual sources. We also produce a normalized stacked spectrum of all sources. Results: Assuming an intrinsic average L(1470)/L(895) of 3, we estimate the individual and average relative escape fraction. We do not detect ionizing radiation from any individual source, although we identify a possible LyC emitter with very high Lya equivalent width (EW). From the stacked spectrum and assuming a mean transmissivity for the sample, we measure a relative escape fraction f escrel = 0.09 ± 0.04. We also look for correlations between the limits in the LyC flux and source properties and find a tentative correlation between LyC flux and the EW of the Lya emission line. Conclusions: Our results imply that the LyC flux emitted by V = 25-26 star-forming galaxies at z ~ 4 is at most very modest, in agreement with previous upper limits from studies based on broad and narrow band imaging. [ABSTRACT FROM AUTHOR]

Context: The study of statistically significant samples of star-forming dwarf galaxies (SFDGs) at different cosmic epochs is essential for the detailed understanding of galaxy assembly and chemical evolution. However, the main properties of this large population of galaxies at intermediate redshift are still poorly known. Aims: We present the discovery and spectrophotometric characterization of a large sample of 164 faint (iAB~ 23-25 mag) SFDGs at redshift 0.13 = z = 0.88 selected by the presence of bright optical emission lines in the VIMOS Ultra Deep Survey (VUDS). We investigate their integrated physical properties and ionization conditions, which are used to discuss the low-mass end of the mass-metallicity relation (MZR) and other key scaling relations. Methods: We use optical VUDS spectra in the COSMOS, VVDS-02h, and ECDF-S fields, as well as deep multi-wavelength photometry that includes HST-ACS F814W imaging, to derive stellar masses, extinction-corrected star-formation rates (SFR), and gas-phase metallicities of SFDGs. For the latter, we use the direct method and a Te-consistent approach based on the comparison of a set of observed emission lines ratios with the predictions of detailed photoionization models. Results: The VUDS SFDGs are compact (median re~ 1.2 kpc), low-mass (M*~ 107-109M⊙) galaxies with a wide range of star-formation rates (SFR(Ha) ~ 10-3-101M⊙/yr) and morphologies. Overall, they show a broad range of subsolar metallicities (12 +log (O/H) =7.26-8.7; 0.04 ≲Z/Z⊙≲ 1). Nearly half of the sample are extreme emission-line galaxies (EELGs) characterized by high equivalent widths and emission line ratios indicative of higher excitation and ionization conditions. The MZR of SFDGs shows a flatter slope compared to previous studies of galaxies in the same mass range and redshift. We find the scatter of the MZR is partly explained in the low mass range by varying specific SFRs and gas fractions amongst the galaxies in our sample. In agreement with recent studies, we find the subclass of EELGs to be systematically offset to lower metallicity compared to SFDGs at a given stellar mass and SFR, suggesting a younger starburst phase. Compared with simple chemical evolution models we find that most SFDGs do not follow the predictions of a "closed-box" model, but those from a gas-regulating model in which gas flows are considered. While strong stellar feedback may produce large-scale outflows favoring the cessation of vigorous star formation and promoting the removal of metals, younger and more metal-poor dwarfs may have recently accreted large amounts of fresh, very metal-poor gas, that is used to fuel current star formation. [ABSTRACT FROM AUTHOR]

Context. Identifying spurious reduction artefacts in galaxy spectra is a challenge for large surveys. Aims. We present an algorithm for identifying and repairing spurious residual features in sky-subtracted galaxy spectra by using data from the VIMOS Public Extragalactic Redshift Survey (VIPERS) as a test case. Methods. The algorithm uses principal component analysis (PCA) applied to the galaxy spectra in the observed frame to identify sky line residuals imprinted at characteristic wavelengths. We further model the galaxy spectra in the rest-frame using PCA to estimate the most probable continuum in the corrupted spectral regions, which are then repaired. Results. We apply the method to 90 000 spectra from the VIPERS survey and compare the results with a subset for which careful editing was performed by hand. We find that the automatic technique reproduces the time-consuming manual cleaning in a uniform and objective manner across a large data sample. The mask data products produced in this work are released together with the VIPERS second public data release (PDR-2). [ABSTRACT FROM AUTHOR]

This paper describes the first data release (DR1) of the VIMOS Ultra Deep Survey (VUDS). The VUDS-DR1 is the release of all low-resolution spectroscopic data obtained in 276.9 arcmin² of the CANDELS-COSMOS and CANDELS-ECDFS survey areas, including accurate spectroscopic redshifts zspec 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 zspec > 2, 48 of which have zspec > 4; the highest reliable redshifts reach beyond zspec = 6. This data set approximately doubles the number of galaxies with spectroscopic redshifts at z > 3 in these fields. We discuss the general properties of the VUDS-DR1 sample in terms of the spectroscopic redshift distribution, the distribution of Lyman-α equivalent widths, and physical properties including stellar masses M* and star formation rates derived from spectral energy distribution fitting with the knowledge of zspec. We highlight the properties of the most massive star-forming galaxies, noting the wide range in spectral properties, with Lyman-α 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 VUDS-DR1 data are publicly available and can be retrieved from a dedicated query-based database. Future VUDS data releases will follow this VUDS-DR1 to give access to the spectra and associated measurement of 8000 objects in the full ~1 square degree of the VUDS survey. [ABSTRACT FROM AUTHOR]

We investigate the e ect of di erent star formation histories (SFHs) on the relation between stellar mass (M8 ) and star formation rate (SFR) using a sample of galaxies with reliable spectroscopic redshift zspec > 2 drawn from the VIMOS Ultra-Deep Survey (VUDS). We produce an extensive database of dusty model galaxies, calculated starting from a new library of single stellar population (SSPs) models, weighted by a set of 28 di erent star formation histories based on the Schmidt function, and characterized by di erent ratios of the gas infall timescale τinfall to the star formation effciency ν. Dust extinction and re-emission were treated by means of the radiative transfer calculation. The spectral energy distribution (SED) fitting technique was performed by using GOSSIP+, a tool able to combine both photometric and spectroscopic information to extract the best value of the physical quantities of interest, and to consider the intergalactic medium (IGM) attenuation as a free parameter. We find that the main contribution to the scatter observed in the SFR-M8 plane is the possibility of choosing between di erent families of SFHs in the SED fitting procedure, while the redshift range plays a minor role. The majority of the galaxies, at all cosmic times, are best fit by models with SFHs characterized by a high τinfall/ν ratio. We discuss the reliability of a low percentage of dusty and highly star-forming galaxies in the context of their detection in the far infrared (FIR). [ABSTRACT FROM AUTHOR]

We study the evolution of the star formation rate (SFR) - stellar mass (M*) relation and specific star formation rate (sSFR) of star-forming galaxies (SFGs) since a redshift z - 5.5 using 2435 (4531) galaxies with highly reliable spectroscopic redshifts in the VIMOS Ultra-Deep Survey (VUDS). It is the first time that these relations can be followed over such a large redshift range from a single homogeneously selected sample of galaxies with spectroscopic redshifts. The log(SFR) - log(M*) relation for SFGs remains roughly linear all the way up to z = 5, but the SFR steadily increases at fixed mass with increasing redshift. We find that for stellar masses M* > 3.2 x 109 M0 the SFR increases by a factor of ~13 between z = 0.4 and z = 2.3. We extend this relation up to z = 5, finding an additional increase in SFR by a factor of 1.7 from z = 2.3 to z = 4.8 for masses M* > 1010 M0. We observe a turn-off in the SFR-M* relation at the highest mass end up to a redshift z ~ 3.5. We interpret this turn-off as the signature of a strong on-going quenching mechanism and rapid mass growth. The sSFR increases strongly up to z ~ 2, but it grows much less rapidly in 2 < z < 5. We find that the shape of the sSFR evolution is not well reproduced by cold gas accretion-driven models or the latest hydrodynamical models. Below z ~ 2 these models have a flatter evolution (1 + z)® with ® = 2-2.25 compared to the data which evolves more rapidly with ® = 2.8 ± 0.2. Above z ~ 2, the reverse is happening with the data evolving more slowly with ® = 1.2 ± 0.1. The observed sSFR evolution over a large redshift range 0 < z < 5 and our finding of a non-linear main sequence at high mass both indicate that the evolution of SFR and M* is not solely driven by gas accretion. The results presented in this paper emphasize the need to invoke a more complex mix of physical processes including major and minor merging to further understand the co-evolution of the SFR and stellar mass growth. [ABSTRACT FROM AUTHOR]

High-density environments are crucial places for studying the link between hierarchical structure formation and stellar mass growth in galaxies. In this work, we characterise a massive proto-cluster at z = 2.895 that we found in the COSMOS field using the spectroscopic sample of the VIMOS Ultra-Deep Survey (VUDS). This is one of the rare structures at z ∼ 3 not identified around an active galactic nucleus (AGN) or a radio galaxy, thus it represents an ideal laboratory for investigating the formation of galaxies in dense environments. The structure comprises 12 galaxies with secure spectroscopic redshift in an area of ∼7' × 8', in a total z range of Δz = 0.016. The measured galaxy number overdensity is δg = 12 ± 2. This overdensity has a total mass of M ∼ 8.1 × 1014 M☉ in a volume of 13 × 15 × 17 Mpc3. Simulations indicate that such an overdensity at z ∼ 2.9 is a proto-cluster, which will collapse in a cluster of total mass Mz=0 ∼ 2.5 × 1015 M☉ at z = 0, i.e. a massive cluster in the local Universe. We analysed the properties of the galaxies within the overdensity, and we compared them with a control sample at the same redshift but outside the overdensity. We could not find any statistically significant difference between the properties (stellar mass, star formation rate, specific star formation rate, NUV-r and r - K colours) of the galaxies inside and outside the overdensity, but this result might be due to the lack of statistics or possibly to the specific galaxy population sampled by VUDS, which could be less affected by environment than the other populations not probed by the survey. The stacked spectrum of galaxies in the background of the overdensity shows a significant absorption feature at the wavelength of Lyα redshifted at z = 2.895 (λ = 4736 Å), with a rest frame equivalent width (EW) of 4 ± 1.4 Å. Stacking only background galaxies without intervening sources at z ∼ 2.9 along their line of sight, we find that this absorption feature has a rest frame EW of 10.8 ± 3.7 Å, with a detection S/N of ∼4. We verify that this measurement is not likely to be due to noise fluctuations. These EW values imply a high column density (N(HI) ∼ 3-20 × 1019 cm-2), consistent with a scenario where such absorption is due to intervening cold streams of gas that are falling into the halo potential wells of the proto-cluster galaxies. Nevertheless, we cannot rule out the hypothesis that this absorption line is related to the diffuse gas within the overdensity. [ABSTRACT FROM AUTHOR]

We report the discovery of 31 low-luminosity (-14.5 ≳ MAB(B) ≳ -18.8), extreme emission line galaxies (EELGs) at 0.2 ≲ z ≲ 0.9 identified by their unusually high rest-frame equivalent widths (100 =EW[O iii] = 1700 Å) as part of the VIMOS Ultra Deep Survey (VUDS). VIMOS optical spectra of unprecedented sensitivity (IAB ~ 25 mag) along with multiwavelength photometry and HST imaging are used to investigate spectrophotometric properties of this unique sample and to explore, for the first time, the very low stellar mass end (M⋆ ≲ 108 M⊙) of the luminosity-metallicity (LZR) and mass-metallicity (MZR) relations at z < 1. Characterized by their extreme compactness (R50 < 1 kpc), low stellar mass and enhanced specific star formation rates (sSFR = SFR/M⋆ ~ 10-9-10-7 yr-1), the VUDS EELGs are blue dwarf galaxies likely experiencing the first stages of a vigorous galaxy-wide starburst. Using Te-sensitive direct and strong-line methods, we find that VUDS EELGs are low-metallicity (7.5 ≲ 12 + log (O/H) ≲ 8.3) galaxies with high ionization conditions (log (qion) ≳ 8 cms-1), including at least three EELGs showing HeIIλ 4686 Å emission and four extremely metal-poor (≲10% solar) galaxies. The LZR and MZR followed by VUDS EELGs show relatively large scatter, being broadly consistent with the extrapolation toward low luminosity and mass from previous studies at similar redshift. However, we find evidence that galaxies with younger and more vigorous star formation - as characterized by their larger EWs, ionization and sSFR - tend to be more metal poor at a given stellar mass. [ABSTRACT FROM AUTHOR]

Context. The mass assembly of galaxies can proceed through different physical processes. Here we report on the spectroscopic identification of close physical pairs of galaxies at redshifts 2 ≲ z < 4 and discuss the impact of major mergers in building galaxies at these early cosmological times. Aims. We aim to identify and characterize close physical pairs of galaxies destined to merge and use their properties to infer the contribution of merging processes to the early mass assembly of galaxies. Methods. We searched for galaxy pairs with a transverse separation rp ≤ 25 h−1 kpc and a velocity difference Δv ≤ 500 km s−1 using early data from the VIMOS Ultra Deep Survey (VUDS) that comprise a sample of 1111 galaxies with spectroscopic redshifts measurements at redshifts 1.8 ≤ z ≤ 4 in the COSMOS, ECDFS, and VVDS–02h fields, combined with VVDS data.We analysed their spectra and associated visible and near-infrared photometry to assess the main properties of merging galaxies that have an average stellar mass M⋆ = 2.3 × 1010 M⊙ at these redshifts. Results. Using the 12 physical pairs found in our sample we obtain a first robust measurement of the major merger fraction at these redshifts, fMM = 19.4−6+9%. These pairs are expected to merge within 1 Gyr on average each producing a more massive galaxy by the time the cosmic star formation peaks at z ∼ 1−2. Using the pairs’ merging time scales, we derive a merging rate of RMM = 0.17−0.05+0.08 Gyr−1. From the average mass ratio between galaxies in the pairs, the stellar mass of the resulting galaxy after merging will be ∼60% higher than the most massive galaxy in the pair before merging.We conclude that major merging of galaxy pairs is on-going at 2 ≲ z < 4 and is significantly contributing to the major mass assembly phase of galaxies at this early epoch. [ABSTRACT FROM AUTHOR]

Context. Deep representative surveys of galaxies at different epochs are needed to make progress in understanding galaxy evolution. Aims. We describe the completed VIMOS VLT Deep Survey and the final data release of 35 016 galaxies and type-I AGN with measured spectroscopic redshifts covering all epochs up to redshift z ∼ 6.7, in areas from 0.142 to 8.7 square degrees, and volumes from 0.5×106 to 2×107 h-3 Mpc3. Methods. We selected samples of galaxies based solely on their i-band magnitude reaching iAB = 24.75. Spectra were obtained with VIMOS on the ESO-VLT integrating 0.75 h, 4.5 h, and 18 h for the Wide, Deep, and Ultra-Deep nested surveys, respectively. We demonstrate that any "redshift desert" can be crossed successfully using spectra covering 3650 ⩽ λ ⩽ 9350 Å. A total of 1263 galaxies were again observed independently within the VVDS and from the VIPERS and MASSIV surveys. They were used to establish the redshift measurements reliability, to assess completeness in the VVDS sample, and to provide a weighting scheme taking the survey selection function into account. We describe the main properties of the VVDS samples, and the VVDS is compared to other spectroscopic surveys in the literature. Results. In total we have obtained spectroscopic redshifts for 34 594 galaxies, 422 type-I AGN, and 12 430 Galactic stars. The survey enabled identifying galaxies up to very high redshifts with 4669 redshifts in 1 ⩽ zspec ⩽ 2, 561 in 2 ⩽ zspec ⩽ 3, and 468 with zspec > 3, and specific populations like Lyman-α emitters were identified out to z = 6.62.We show that the VVDS occupies a unique place in the parameter space defined by area, depth, redshift coverage, and number of spectra. Conclusions. The VIMOS VLT Deep Survey provides a comprehensive survey of the distant universe, covering all epochs since z ∼ 6, or more than 12 Gyr of cosmic time, with a uniform selection, which is the largest such sample to date. A wealth of science results derived from the VVDS have shed new light on the evolution of galaxies and AGN and on their distribution in space over this large cosmic time. The VVDS further demonstrates that large deep spectroscopic redshift surveys over all these epochs in the distant Universe are a key tool to observational cosmology. To enhance the legacy value of the survey, a final public release of the complete VVDS spectroscopic redshift sample is available at http:// cesam.lam.fr/vvds. [ABSTRACT FROM AUTHOR]

Aims. The aim of this work is to identify He II emitters at 2 < z < 4.6 and to constrain the source of the hard ionizing continuum that powers the He II emission. Methods. We assembled a sample of 277 galaxies with a highly reliable spectroscopic redshift at 2 < z < 4.6 from the VIMOS-VLT Deep Survey (VVDS) Deep and Ultra-Deep data, and we identified 39 He II ?1640 emitters. We studied their spectral properties, measuring the fluxes, equivalent widths (EW), and full width at half maximum (FWHM) for most relevant lines, including He II λ1640, Lyα line, Si II λ1527, and C IV λ1549. Results. About 10% of galaxies at z ∼ 3 and iAB ≤ 24.75 show He II in emission, with rest frame equivalent widths EW0 ∼ 1- 7 Å, equally distributed between galaxies with Lyα in emission or in absorption. We find 11 (3.9% of the global population) reliable He II emitters with unresolved He II lines (FWHM0 < 1200 km s-1), 13 (4.6% of the global population) reliable emitters with broad He II emission (FWHM0 > 1200 km s-1), 3 active galactic nuclei (AGN), and an additional 12 possible He II emitters. The properties of the individual broad emitters are in agreement with expectations from a Wolf-Rayet (W-R) model. Instead, the properties of the narrow emitters are not compatible with this model, nor with predictions of gravitational cooling radiation produced by gas accretion, unless this is severely underestimated by current models by more than two orders of magnitude. Rather, we find that the EW of the narrow He II line emitters are in agreement with expectations for a Population III (PopIII) star formation, if the episode of star formation is continuous, and we calculate that a PopIII star formation rate (SFR) of 0.1-10 M⊚ yr-1 alone is enough to sustain the observed He II flux. Conclusions. We conclude that narrow He II emitters are powered either by the ionizing flux from a stellar population rare at z ∼ 0 but much more common at z ∼ 3, or by PopIII star formation. As proposed by Tornatore and collaborators, incomplete interstellar medium mixing may leave some small pockets of pristine gas at the periphery of galaxies from which PopIII may form, even down to z ∼ 2 or lower. If this interpretation is correct, we measure at z ∼ 3 a star formation rate density in PopIII stars of 10-6 M⊚ yr-1 Mpc-3, higher than, but qualitatively comparable to the value predicted by Tornatore and collaborators. [ABSTRACT FROM AUTHOR]

Aims. We investigate the global galaxy evolution over ~12 Gyr (0.05 ⩽ z ⩽ 4.5), from the far ultraviolet (FUV) luminosity function (LF), luminosity density (LD), and star formation rate density (SFRD), using the VIMOS-VLT Deep Survey (VVDS), a single deep galaxy redshift survey with a well controlled selection function. Methods. We combine the VVDS Deep (17.5 ⩽ IAB ⩽ 24.0) and Ultra-Deep (23.00 ⩽ i' AB ⩽ 24.75) redshift surveys, totalizing ~11 000 galaxies, to estimate the rest-frame FUV LF and LD, using a wide wavelength range of deep photometry (337 < λ < 2310 nm).We extract the dust attenuation of the FUV radiation, embedded in the well-constrained spectral energy distributions. We then derive the dust-corrected SFRD. Results. We find a constant and flat faint-end slope a in the FUV LF at z < 1.7. At z > 1.7, we set a steepening with (1+z). The absolute magnitude M☉ FUV steadily brightens in the entire range 0 < z < 4.5, and at z > 2 it is on average brighter than in the literature, while ϕ" is on average smaller. The evolution of our total LD shows a peak at z ≃ 2, clearly present also when considering all sources of uncertainty. The SFRD history peaks as well at z ≃ 2. It first steadily rises by a factor of ~6 during 2 Gyr (from z = 4.5 to z = 2), and then decreases by a factor of ~12 during 10 Gyr down to z = 0.05. This peak is mainly produced by a similar peak within the population of galaxies with -21.5 ⩽ MFUV ⩽ -19.5. As times goes by, the total SFRD is dominated by fainter and fainter galaxies. The mean dust attenuation of the global galaxy population rises fast by 1 mag during 2 Gyr from z ≃ 4.5 to z ~ 2, reaches slowly its maximum at z ≃ 1 (AFUV ≃ 2.2 mag), and then decreases by 1.1 mag during 7 Gyr down to z ≃ 0. Conclusions. We have derived the cosmic SFRD history and the total dust amount in galaxies over a continuous period of ~12 Gyr, using a single homogeneous spectroscopic redshift sample. The presence of a clear peak at z ≃ 2 and a fast rise at z > 2 of the SFRD is compelling for models of galaxy formation. This peak is mainly produced by bright galaxies (L >~ L☉ z=2), requiring that significant gas reservoirs still exist at this epoch and are probably replenished by cold accretion and wet mergers, while feedback or quenching processes are not yet strong enough to lower the SF. The dust attenuation maximum is reached ~2 Gyr after the SFRD peak, implying a contribution from the intermediate-mass stars to the dust production at z < 2. [ABSTRACT FROM AUTHOR]