The extended epoch of galaxy formation: age dating of ~3600 galaxies with 2<z<6.5 in the VIMOS Ultra-Deep Survey

We aim at improving constraints on the epoch of galaxy formation by measuring the ages of 3597 galaxies with 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 microns using composite stellar population models. We conclude from extensive simulations that at z>2 the joint analysis of spectroscopy and photometry combined with restricted age possibilities when taking into account the age of the Universe substantially reduces systematic uncertainties and degeneracies in the age derivation. We find galaxy ages ranging from very young with a few tens of million years to substantially evolved with ages up to ~1.5-2 Gyr. The formation redshifts z_f derived from the measured ages indicate that galaxies may have started forming stars as early as z_f~15. We produce the formation redshift function (FzF), the number of galaxies per unit volume formed at a redshift z_f, and compare the FzF in increasing redshift bins finding a remarkably constant 'universal' FzF. The FzF is parametrized with (1+z)^\zeta, with \zeta~0.58+/-0.06, indicating a smooth 2 dex increase from z~15 to z~2. Remarkably this observed increase is of the same order as the observed rise in the star formation rate density (SFRD). The ratio of the SFRD with the FzF gives an average SFR per galaxy of ~7-17Msun/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 from the highest possible 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. (Abridged)Comment: Submitted to A&A, 24 page

Improved constraints on the expansion rate of the Universe up to z~1.1 from the spectroscopic evolution of cosmic chronometers

We present new improved constraints on the Hubble parameter H(z) in the redshift range 0.15 < z < 1.1, obtained from the differential spectroscopic evolution of early-type galaxies as a function of redshift. We extract a large sample of early-type galaxies (\sim11000) from several spectroscopic surveys, spanning almost 8 billion years of cosmic lookback time (0.15 < z < 1.42). We select the most massive, red elliptical galaxies, passively evolving and without signature of ongoing star formation. Those galaxies can be used as standard cosmic chronometers, as firstly proposed by Jimenez & Loeb (2002), whose differential age evolution as a function of cosmic time directly probes H(z). We analyze the 4000 {\AA} break (D4000) as a function of redshift, use stellar population synthesis models to theoretically calibrate the dependence of the differential age evolution on the differential D4000, and estimate the Hubble parameter taking into account both statistical and systematical errors. We provide 8 new measurements of H(z) (see Tab. 4), and determine its change in H(z) to a precision of 5-12% mapping homogeneously the redshift range up to z \sim 1.1; for the first time, we place a constraint on H(z) at z \neq 0 with a precision comparable with the one achieved for the Hubble constant (about 5-6% at z \sim 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial to distinguish many different quintessence cosmologies. These measurements have been tested to best match a \Lambda CDM model, clearly providing a statistically robust indication that the Universe is undergoing an accelerated expansion. This method shows the potentiality to open a new avenue in constrain a variety of alternative cosmologies, especially when future surveys (e.g. Euclid) will open the possibility to extend it up to z \sim 2.Comment: 34 pages, 15 figures, 6 tables, published in JCAP. It is a companion to Moresco et al. (2012b, http://arxiv.org/abs/1201.6658) and Jimenez et al. (2012, http://arxiv.org/abs/1201.3608). The H(z) data can be downloaded at http://www.physics-astronomy.unibo.it/en/research/areas/astrophysics/cosmology-with-cosmic-chronometer

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Measuring non-linear galaxy bias at z ~ 0.8

Aims. We use the first release of the VImos Public Extragalactic Redshift Survey of galaxies (VIPERS) of 3c50 000 objects to measure the biasing relation between galaxies and mass in the redshift range z = [0.5,1.1]. Methods. We estimate the 1-point distribution function [PDF] of VIPERS galaxies from counts in cells and, assuming a model for the mass PDF, we infer their mean bias relation. The reconstruction of the bias relation is performed through a novel method that accounts for Poisson noise, redshift distortions, inhomogeneous sky coverage. and other selection effects. With this procedure we constrain galaxy bias and its deviations from linearity down to scales as small as 4 h-1 Mpc and out to z = 1.1. Results. We detect small (up to 2%) but statistically significant (up to 3\u3c3) deviations from linear bias. The mean biasing function is close to linear in regions above the mean density. The mean slope of the biasing relation is a proxy to the linear bias parameter. This slope increases with luminosity, which is in agreement with results of previous analyses. We detect a strong bias evolution only for z> 0.9, which is in agreement with some, but not all, previous studies. We also detect a significant increase of the bias with the scale, from 4 to 8 h-1 Mpc, now seen for the first time out to z = 1. The amplitude of non-linearity depends on redshift, luminosity, and scale, but no clear trend is detected. Owing to the large cosmic volume probed by VIPERS, we find that the mismatch between the previous estimates of bias at z 3c 1 from zCOSMOS and VVDS-Deep galaxy samples is fully accounted for by cosmic variance. Conclusions. The results of our work confirm the importance of going beyond the over-simplistic linear bias hypothesis showing that non-linearities can be accurately measured through the applications of the appropriate statistical tools to existing datasets like VIPERS. \ua9 ESO, 2016

The VANDELS ESO public spectroscopic survey

VANDELS is a uniquely deep spectroscopic survey of high-redshift galaxies with the VIMOS spectrograph on ESO’s Very Large Telescope (VLT). The survey has obtained ultradeep optical (0.48 < λ < 1.0 μ m) spectroscopy of ≃2100 galaxies within the redshift interval 1.0 ≤ z ≤ 7.0, over a total area of ≃0.2 deg2 centred on the CANDELS Ultra Deep Survey and Chandra Deep Field South fields. Based on accurate photometric redshift pre-selection, 85 per cent of the galaxies targeted by VANDELS were selected to be at z ≥ 3. Exploiting the red sensitivity of the refurbished VIMOS spectrograph, the fundamental aim of the survey is to provide the high-signal-to-noise ratio spectra necessary to measure key physical properties such as stellar population ages, masses, metallicities, and outflow velocities from detailed absorption-line studies. Using integration times calculated to produce an approximately constant signal-to-noise ratio (20 < tint< 80 h), the VANDELS survey targeted: (a) bright star-forming galaxies at 2.4 ≤ z ≤ 5.5, (b) massive quiescent galaxies at 1.0 ≤ z ≤ 2.5, (c) fainter star-forming galaxies at 3.0 ≤ z ≤ 7.0, and (d) X-ray/Spitzer-selected active galactic nuclei and Herschel-detected galaxies. By targeting two extragalactic survey fields with superb multiwavelength imaging data, VANDELS will produce a unique legacy data set for exploring the physics underpinning high-redshift galaxy evolution. In this paper, we provide an overview of the VANDELS survey designed to support the science exploitation of the first ESO public data release, focusing on the scientific motivation, survey design, and target selection

UV and Ly \u3b1 luminosity functions of galaxies and star formation rate density at the end of HI reionization from the VIMOS UltraDeep Survey (VUDS)

Context. The star formation rate density (SFRD) evolution presents an area of great interest in the studies of galaxy evolution and reionization. The current constraints of SFRD at z &gt; 5 are based on the rest-frame UV luminosity functions with the data from photometric surveys. The VIMOS UltraDeep Survey (VUDS) was designed to observe galaxies at redshifts up to 6 and opened a window for measuring SFRD at z &gt; 5 from a spectroscopic sample with a well-controlled selection function. Aims. We establish a robust statistical description of the star-forming galaxy population at the end of cosmic HI reionization (5.0 64 z 64 6.6) from a large sample of 49 galaxies with spectroscopically confirmed redshifts. We determine the rest-frame UV and Ly\u3b1 luminosity functions and use them to calculate SFRD at the median redshift of our sample z = 5.6. Methods. We selected a sample of galaxies at 5.0 64 zspec 64 6.6 from the VUDS. We cleaned our sample from low redshift interlopers using ancillary photometric data. We identified galaxies with Ly\u3b1 either in absorption or in emission, at variance with most spectroscopic samples in the literature where Ly\u3b1 emitters (LAE) dominate. We determined luminosity functions using the 1/Vmaxmethod. Results. The galaxies in this redshift range exhibit a large range in their properties. A fraction of our sample shows strong Ly\u3b1 emission, while another fraction shows Ly\u3b1 in absorption. UV-continuum slopes vary with luminosity, with a large dispersion. We find that star-forming galaxies at these redshifts are distributed along the main sequence in the stellar mass vs. SFR plane, described with a slope \u3b1 = 0.85\ub10.05.We report a flat evolution of the specific SFR compared to lower redshift measurements. We find that the UV luminosity function is best reproduced by a double power law, while a fit with a Schechter function is only marginally inferior. The Ly\u3b1 luminosity function is best fitted with a Schechter function. We derive a log SFRDUV(\u1e40 yr-1Mpc-3) = -1.45+0.06-0.08and log SFRDLy\u3b1(\u1e40 yr-1Mpc-3) = -1.40+0.07-0.08. The SFRD derived from the Ly\u3b1 luminosity function is in excellent agreement with the UV-derived SFRD after correcting for IGM absorption. Conclusions. Our new SFRD measurements at a mean redshift of z = 5.6 are 3c0.2 dex above the mean SFRD reported in Madau and Dickinson (2014, ARAandA, 52, 415), but in excellent agreement with results from Bouwens et al. (2015a, ApJ, 803, 34). These measurements confirm the steep decline of the SFRD at z &gt; 2. The bright end of the Ly\u3b1 luminosity function has a high number density, indicating a significant star formation activity concentrated in the brightest LAE at these redshifts. LAE with equivalent width EW&gt; 25 contribute to about 75% of the total UV-derived SFRD. While our analysis favors low dust content in 5.0 &lt; z &lt; 6.6, uncertainties on the dust extinction correction and associated degeneracy in spectral fitting will remain an issue, when estimating the total SFRD until future surveys extending spectroscopy to the NIR rest-frame spectral domain, such as with JWST

UV and Lyα\alpha luminosity functions of galaxies and star formation rate density at the end of HI reionization from the VIMOS UltraDeep Survey (VUDS)

International audienceContext. The star formation rate density (SFRD) evolution presents an area of great interest in the studies of galaxy evolution and reionization. The current constraints of SFRD at z >  5 are based on the rest-frame UV luminosity functions with the data from photometric surveys. The VIMOS UltraDeep Survey (VUDS) was designed to observe galaxies at redshifts up to ∼6 and opened a window for measuring SFRD at z >  5 from a spectroscopic sample with a well-controlled selection function.Aims. We establish a robust statistical description of the star-forming galaxy population at the end of cosmic HI reionization (5.0 ≤ z ≤ 6.6) from a large sample of 49 galaxies with spectroscopically confirmed redshifts. We determine the rest-frame UV and Lyα luminosity functions and use them to calculate SFRD at the median redshift of our sample z = 5.6.Methods. We selected a sample of galaxies at 5.0 ≤ zspec ≤ 6.6 from the VUDS. We cleaned our sample from low redshift interlopers using ancillary photometric data. We identified galaxies with Lyα either in absorption or in emission, at variance with most spectroscopic samples in the literature where Lyα emitters (LAE) dominate. We determined luminosity functions using the 1/Vmax method.Results. The galaxies in this redshift range exhibit a large range in their properties. A fraction of our sample shows strong Lyα emission, while another fraction shows Lyα in absorption. UV-continuum slopes vary with luminosity, with a large dispersion. We find that star-forming galaxies at these redshifts are distributed along the main sequence in the stellar mass vs. SFR plane, described with a slope α = 0.85 ± 0.05. We report a flat evolution of the specific SFR compared to lower redshift measurements. We find that the UV luminosity function is best reproduced by a double power law, while a fit with a Schechter function is only marginally inferior. The Lyα luminosity function is best fitted with a Schechter function. We derive a logSFRDUV(M⊙ yr−1 Mpc−3) = −1.45+0.06−0.08 and logSFRDLyα(M⊙ yr−1 Mpc−3) = −1.40+0.07−0.08. The SFRD derived from the Lyα luminosity function is in excellent agreement with the UV-derived SFRD after correcting for IGM absorption.Conclusions. Our new SFRD measurements at a mean redshift of z = 5.6 are ∼0.2 dex above the mean SFRD reported in Madau & Dickinson (2014, ARA&A, 52, 415), but in excellent agreement with results from Bouwens et al. (2015a, ApJ, 803, 34). These measurements confirm the steep decline of the SFRD at z >  2. The bright end of the Lyα luminosity function has a high number density, indicating a significant star formation activity concentrated in the brightest LAE at these redshifts. LAE with equivalent width EW > 25 Å contribute to about 75% of the total UV-derived SFRD. While our analysis favors low dust content in 5.0 <  z <  6.6, uncertainties on the dust extinction correction and associated degeneracy in spectral fitting will remain an issue, when estimating the total SFRD until future surveys extending spectroscopy to the NIR rest-frame spectral domain, such as with JWST.Key words: galaxies: high-redshift / galaxies: evolution / galaxies: formation / galaxies: star formation / dark ages, reionization, first stars / galaxies: luminosity function, mass function⋆ Based on data obtained with the European Southern Observatory Very Large Telescope, Paranal, Chile, under Large Program 185.A−0791

The ALPINE-ALMA [CII] survey: Survey strategy, observations, and sample properties of 118 star-forming galaxies at 4 < z < 6

The ALMA-ALPINE [CII] survey is aimed at characterizing the properties of a sample of normal star-forming galaxies (SFGs). The ALMA Large Program to INvestigate (ALPINE) features 118 galaxies observed in the [CII]-158 \u3bcm line and far infrared (FIR) continuum emission during the period of rapid mass assembly, right after the end of the HI reionization, at redshifts of 4 &lt; z &lt; 6. We present the survey science goals, the observational strategy, and the sample selection of the 118 galaxies observed with ALMA, with an average beam minor axis of about 0.85\u2033, or 3c5 kpc at the median redshift of the survey. The properties of the sample are described, including spectroscopic redshifts derived from the UV-rest frame, stellar masses, and star-formation rates obtained from a spectral energy distribution (SED) fitting. The observed properties derived from the ALMA data are presented and discussed in terms of the overall detection rate in [CII] and FIR continuum, with the observed signal-to-noise distribution. The sample is representative of the SFG population in the main sequence at these redshifts. The overall detection rate in [CII] is 64% for a signal-to-noise ratio (S/N) threshold larger than 3.5 corresponding to a 95% purity (40% detection rate for S/N &gt; 5). Based on a visual inspection of the [CII] data cubes together with the large wealth of ancillary data, we find a surprisingly wide range of galaxy types, including 40% that are mergers, 20% extended and dispersion-dominated, 13% compact, and 11% rotating discs, with the remaining 16% too faint to be classified. This diversity indicates that a wide array of physical processes must be at work at this epoch, first and foremost, those of galaxy mergers. This paper sets a reference sample for the gas distribution in normal SFGs at 4 &lt; z &lt; 6, a key epoch in galaxy assembly, which is ideally suited for studies with future facilities, such as the James Webb Space Telescope (JWST) and the Extremely Large Telescopes (ELTs)

The VIMOS Ultra-Deep Survey (VUDS): ~10,000 Galaxies with Spectroscopic Redshifts to Study Galaxy Assembly at Early Epochs 2 \u3c z ≈ 6

We present the VIMOS Ultra Deep Survey (VUDS), a spectroscopic redshift survey of ~10 000 very faint galaxies to study the main phase of galaxy assembly in 2 \u3c z ≃ 6. The survey covers 1 deg2 in three separate fields: COSMOS, ECDFS, and VVDS-02h, with the selection of targets based on an inclusive combination of photometric redshifts and colour properties. Spectra covering 3650 \u3c λ \u3c 9350 Å are obtained with VIMOS on the ESO-VLT with integration times of 14h. Here we present the survey strategy, target selection, data processing, and the redshift measurement process with an emphasis on the specific methods used to adapt to this high-redshift range. We discuss the spectra quality and redshift reliability and derive a success rate in redshift measurement of 91%, or 74% by limiting the dataset to the most reliable measurements, down to a limiting magnitude iAB = 25. Measurements are performed all the way down to iAB = 27. The mean redshift of the main sample is z ~ 3 and extends over a broad redshift range mainly in 2 \u3c z \u3c 6. At 3 \u3c z \u3c 5, the galaxies cover a wide range of luminosities −23 \u3c MNUV \u3c −20.5, stellar mass 109M⊙ \u3c M∗ \u3c 1011M⊙, and star formation rates 1M⊙/yr \u3c SFR \u3c 103M⊙/yr. We discuss the spectral properties of galaxies using individual as well asstacked spectra. The comparison between spectroscopic and photometric redshifts as well as colour selection demonstrate the effectiveness of our selection scheme. From about ~ 90% of the data analysed so far, we expect to assemble \u3e6000 galaxies with reliable spectroscopic redshifts in 2 \u3c z \u3c 6 when complete. This makes the VUDS the largest survey at these redshifts and offers the opportunity for unprecedented studies of the star-forming galaxy population and its distribution in large-scale structures during the main phase of galaxy assembly

The VIMOS Ultra-Deep Survey (VUDS): IGM transmission towards galaxies with 2.5

The observed UV rest-frame spectra of distant galaxies are the result of their intrinsic emission combined with absorption along the line of sight produced by the inter-galactic medium (IGM). Here we analyse the evolution of the mean IGM transmission Tr(Ly_alpha) and its dispersion along the line of sight for 2127 galaxies with 2.5= 4 compared to results from QSOs, but a degeneracy between dust extinction and IGM prevents to draw firm conclusions if the internal dust extinction for star-forming galaxies at z\u3e4 takes a mean value significantly in excess of E(B-V)\u3e0.15. Most importantly, we find a large dispersion of IGM transmission along the lines of sight towards distant galaxies with 68% of the distribution within 10 to 17% of the median value in delta z=0.5 bins, similar to what is found on the LOS towards QSOs. We demonstrate the importance of taking into account this large range of IGM transmission when selecting high redshift galaxies based on their colour properties (e.g. LBG or photometric redshift selection) or otherwise face a significant incompleteness in selecting high redshift galaxy population

The Stellar Mass--Halo Mass Relation From Galaxy Clustering in VUDS: A High Star Formation Efficiency at Z≃3

The relation between the galaxy stellar mass M⋆ and the dark matter halo mass Mh gives important information on the efficiency in forming stars and assembling stellar mass in galaxies. We present measurements of the ratio of stellar mass to halo mass (SMHR) at redshifts 2 \u3c z \u3c 5, obtained from the VIMOS Ultra Deep Survey. We use halo occupation distribution (HOD) modelling of clustering measurements on ~3000 galaxies with spectroscopic redshifts to derive the dark matter halo mass Mh, and spectral energy density fitting over a large set of multi-wavelength data to derive the stellar mass M⋆ and compute the SMHR = M⋆/Mh. We find that the SMHR ranges from 1% to 2.5% for galaxies with M⋆ = 1.3 × 109 M⊙ to M⋆ = 7.4 × 109 M⊙ in DM halos with Mh = 1.3 × 1011 M⊙ to Mh = 3 × 1011 M⊙. We derive the integrated star formation efficiency (ISFE) of these galaxies and find that the star formation efficiency is a moderate 6−9% for lower mass galaxies, while it is relatively high at 16% for galaxies with the median stellar mass of the sample ~ 7 × 109 M⊙. The lower ISFE at lower masses may indicate that some efficient means of suppressing star formation is at work (like SNe feedback), while the high ISFE for the average galaxy at z ~ 3 indicates that these galaxies efficiently build up their stellar mass at a key epoch in the mass assembly process. Based on our results, we propose a possible scenario in which the average massive galaxy at z ~ 3 begins to experience truncation of its star formation within a few million years