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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]

We present a study of the dependence of galaxy clustering on luminosity and stellar mass in the redshift range 2 < z < 3:5 using 3236 galaxies with robust spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS), covering a total area of 0:92 deg2. We measured the two-point real-space correlation function wp(rp) for four volume-limited subsamples selected by stellar mass and four volume-limited subsamples selected by MUV absolute magnitude.We find that the scale-dependent clustering amplitude r0 significantly increases with increasing luminosity and stellar mass. For the least luminous galaxies (MUV < -19:0), we measured a correlation length r0= 2:87 ± 0:22 h-1 Mpc and slope γ = 1:59 ± 0:07, while for the most luminous (MUV < -20:2) r0 = 5:35 ± 0:50 h-1 Mpc and γ = 1:92 ± 0:25. These measurements correspond to a strong relative bias between these two subsamples of ▵b/b* = 0:43. Fitting a five-parameter halo occupation distribution (HOD) model, we find that the most luminous (MUV < -20:2) and massive (M* < 1010h-1 M☉) galaxies occupy the most massive dark matter haloes with ≺Mh≻ = 1012:30 h-1 M☉. Similar to the trends observed at lower redshift, the minimum halo mass Mmin depends on the luminosity and stellar mass of galaxies and grows from Mmin= 109:73 h-1 M☉ to Mmin = 1011:58 h-1 M☉ from the faintest to the brightest among our galaxy sample, respectively. We find the difference between these halo masses to be much more pronounced than is observed for local galaxies of similar properties. Moreover, at z ∼ 3, we observe that the masses at which a halo hosts, on average, one satellite and one central galaxy is M1 ≈ 4Mmin over all luminosity ranges, which is significantly lower than observed at z ∼ 0; this indicates that the halo satellite occupation increases with redshift. The luminosity and stellar mass dependence is also reflected in the measurements of the large-scale galaxy bias, which we model as bg;HOD(>L) = 1:92 + 25:36(L=L*)7:01.We conclude our study with measurements of the stellar-to-halo mass ratio (SHMR).We observe a significant model-observation discrepancy for low-mass galaxies, suggesting a higher than expected star formation efficiency of these galaxies. [ABSTRACT FROM AUTHOR]

Context. Future large-scale surveys, such as the ESA Euclid mission, will produce a large set of galaxy redshifts (≥106) that will require fully automated data-processing pipelines to analyze the data, extract crucial information and ensure that all requirements are met. A fundamental element in these pipelines is to associate to each galaxy redshift measurement a quality, or reliability, estimate. Aims. In this work, we introduce a new approach to automate the spectroscopic redshift reliability assessment based on machine learning (ML) and characteristics of the redshift probability density function. Methods. We propose to rephrase the spectroscopic redshift estimation into a Bayesian framework, in order to incorporate all sources of information and uncertainties related to the redshift estimation process and produce a redshift posterior probability density function (PDF). To automate the assessment of a reliability flag, we exploit key features in the redshift posterior PDF and machine learning algorithms. Results. As a working example, public data from the VIMOS VLT Deep Survey is exploited to present and test this new methodology. We first tried to reproduce the existing reliability flags using supervised classification in order to describe di erent types of redshift PDFs, but due to the subjective definition of these flags (classification accuracy ∼58%), we soon opted for a new homogeneous partitioning of the data into distinct clusters via unsupervised classification. After assessing the accuracy of the new clusters via resubstitution and test predictions (classification accuracy ∼98%), we projected unlabeled data from preliminary mock simulations for the Euclid space mission into this mapping to predict their redshift reliability labels. Conclusions. Through the development of a methodology in which a system can build its own experience to assess the quality of a parameter, we are able to set a preliminary basis of an automated reliability assessment for spectroscopic redshift measurements. This newly-defined method is very promising for next-generation large spectroscopic surveys from the ground and in space, such as Euclid and WFIRST. [ABSTRACT FROM AUTHOR]

The properties of stellar clumps in star-forming galaxies and their evolution over the redshift range 2 ≲ z ≲ 6 are presented and discussed in the context of the build-up of massive galaxies at early cosmic times. We focused on galaxies with spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS) and stellar masses log 10(M⋆/M⊙) > −0.204 × (z−4.5) + 9.35. We analyzed HST-ACS images to identify clumps within a 20 kpc radius using a method taking into account differential surface brightness dimming and luminosity evolution with redshift. We find that the population of galaxies with more than one clump is dominated by galaxies with two clumps, representing ~21–25% of the population, while the fraction of galaxies with three, or four and more, clumps is 8–11% and 7–9%, respectively. The fraction of clumpy galaxies is in the range ~35–55% over 2 < z < 6, increasing at higher redshifts, indicating that the fraction of irregular galaxies remains high up to the highest redshifts. The large and bright clumps (M⋆ ~ 109 up to ~1010 M⊙) are found to reside predominantly in galaxies with two clumps. Smaller and lower luminosity clumps (M⋆ < 109 M⊙) are found in galaxies with three clumps or more. We interpret these results as evidence for two different modes of clump formation working in parallel. The small low luminosity clumps are likely the result of disk fragmentation, with violent disk instabilities (VDI) forming several long-lived clumps in-situ as suggested from simulations. A fraction of these clumps is also likely coming from minor mergers as confirmed from spectroscopy in several cases. The clumps in the dominating population of galaxies with two clumps are significantly more massive and have properties akin to those in galaxy pairs undergoing massive merging observed at similar redshifts; they appear as more massive than the most massive clumps observed in numerical simulations of disks with VDI. We infer from these properties that the bright and large clumps are most likely the result of major mergers bringing-in ex situ matter onto a galaxy, and we derive a high major merger fraction of ~20%. The diversity of clump properties therefore suggests that the assembly of star-forming galaxies at z ~ 2–6 proceeds from several different dissipative processes including an important contribution from major and minor mergers. [ABSTRACT FROM AUTHOR]

We aim to develop a novel methodology for measuring the growth rate of structure around cosmic voids. We identified voids in the completed VIMOS Public Extragalactic Redshift Survey (VIPERS), using an algorithm based on searching for empty spheres. We measured the crosscorrelation between the centres of voids and the complete galaxy catalogue. The cross-correlation function exhibits a clear anisotropy in both VIPERS fields (W1 and W4), which is characteristic of linear redshift space distortions. By measuring the projected cross-correlation and then de-projecting it we are able to estimate the un-distorted cross-correlation function. We propose that given a sufficiently well-measured crosscorrelation function one should be able to measure the linear growth rate of structure by applying a simple linear Gaussian streaming model for the redshift space distortions (RSD). Our study of voids in 306 mock galaxy catalogues mimicking the VIPERS fields suggests that VIPERS is capable of measuring β, the ratio of the linear growth rate to the bias, with an error of around 25%. Applying our method to the VIPERS data, we find a value for the redshift space distortion parameter, β = 0.423+0.104 −0.108 which, given the bias of the galaxy population we use, gives a linear growth rate of fσ8 = 0.296+0.075 −0.078 at z = 0.727. These results are consistent with values observed in parallel VIPERS analyses that use standard techniques. [ABSTRACT FROM AUTHOR]

We investigate the evolution of the galaxy stellar mass function and stellar mass density from redshift z = 0.2 to z = 1.5 of a Ks < 22- selected sample with highly reliable photometric redshifts and over an unprecedentedly large area. Our study is based on near-infrared observations carried out with the WIRCam instrument at CFHT over the footprint of the VIPERS spectroscopic survey and benefits from the high-quality optical photometry from the CFHTLS and ultraviolet observations with the GALEX satellite. The accuracy of our photometric redshifts is σ∆z/(1+z) < 0.03 and 0.05 for the bright (iAB < 22.5) and faint (iAB > 22.5) samples, respectively. The galaxy stellar mass function is measured with ∼760 000 galaxies down to Ks ∼ 22 and over an effective area of ∼22.4 deg2, the latter of which drastically reduces the statistical uncertainties (i.e. Poissonian error and cosmic variance). We point out the importance of carefully controlling the photometric calibration, whose effect becomes quickly dominant when statistical uncertainties are reduced, which will be a major issue for future cosmological surveys with EUCLID or LSST, for instance. By exploring the rest-frame (NUV−r) vs. (r − Ks) colour-colour diagram with which we separated star-forming and quiescent galaxies, (1) we find that the density of very massive log(M∗/Mʘ) > 11.5 galaxies is largely dominated by quiescent galaxies and increases by a factor 2 from z ∼ 1 to z ∼ 0.2, which allows for additional mass assembly through dry mergers. (2) We also confirm the scenario in which star formation activity is impeded above a stellar mass log(M*sf/Mʘ) = 10.64 ± 0.01. This value is found to be very stable at 0.2 < z < 1.5. (3) We discuss the existence of a main quenching channel that is followed by massive star-forming galaxies, and we finally (4) characterise another quenching mechanism that is required to explain the clear excess of low-mass quiescent galaxies that is observed at low redshift. [ABSTRACT FROM AUTHOR]

Context. High redshift star-forming galaxies are discovered routinely because of a flux excess in narrowband filters caused by an emission line. In most cases, the width of such filters is broader than typical line widths, and the throughput of the filters varies substantially within the bandpass. This leads to substantial uncertainties in redshifts and fluxes that are derived from the observations with one specific narrowband filter. Aims. The uncertainty in measured line parameters can be sharply reduced by using repeated observations of the same target field with filters that have overlapping passbands but differ slightly in central wavelength or wavelength dependence of the effective filter curve. Such data are routinely collected with some large field imaging cameras that use multiple detectors and a separate filter for each of the detectors. An example is the European Southern Observatory’s VISTA InfraRed CAMera (VIRCAM). Methods. We developed a method of determining more accurate redshift and line flux estimates from the ratio of apparent fluxes measured from observations in different narrowband filters and several matching broadband filters. A parameterized model of the line and continuum flux is used to predict the flux ratios as a function of redshift based on the known filter curves. These model predictions are then used to determine the most likely redshift and line flux. Results. We tested the obtainable quality of parameter estimation for the example of Hα in the VIRCAM NB118 filters both on simulated and actual observations where the latter were based on the UltraVISTA DR2 data set. We combined the narrowband data with deep broadband data in Y, J, and H. We find that with this method, the errors in the measured lines fluxes can be reduced up to almost an order of magnitude. Conclusions. We conclude that existing narrowband data can be used to derive accurate line fluxes if the observations include images taken with sufficiently different filter curves. For the UltraVISTA survey, the best-suited narrowband filter combinations allow an accuracy in wavelength of better than 1 nm and in flux of better than 15% at any redshift within the bandpass of the filters. In contrast, analyzing the data without exploiting the difference in filter curves leads to an uncertainty in wavelength of 10 nm and up to an order of magnitude errors in line flux estimates. [ABSTRACT FROM AUTHOR]

The Vimos-VLT Deep Survey is a spectroscopic survey aiming at collecting more than 50000 spectra down to a limiting magnitude $I_{\mathrm{AB}}=24$, and 100000 down to $I_{\mathrm{AB}}=22.5$, on a total of about 16 deg$^2$ without any color or morphology preselection. We present the $N(z)$ distribution up to $z\sim 5$, obtained from a purely magnitude-limited sample down to $I_{\mathrm{AB}}=24$, which is an important input to weak-lensing studies. We discuss the evolution of the galaxy luminosity function up to $z\sim 2$, which exhibits a very strong increase in the typical galaxy luminosity $\Delta M^*\simeq -2.5$ in the U band compared to the local value. Surveys like the VVDS also allow to study the galaxy bias as a function of redshift without assumption about its linearity, an assumption that we find to be violated in some cases. A low bias is found, and the linear bias is shown to increase with redshift.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html [ABSTRACT FROM PUBLISHER]