A Coherent Study of Emission Lines from Broad-Band Photometry: Specific Star-Formation Rates and [OIII]/H{\beta} Ratio at 3 < z < 6

We measure the H{\alpha} and [OIII] emission line properties as well as specific star-formation rates (sSFR) of spectroscopically confirmed 3<z<6 galaxies in COSMOS from their observed colors vs. redshift evolution. Our model describes consistently the ensemble of galaxies including intrinsic properties (age, metallicity, star-formation history), dust-attenuation, and optical emission lines. We forward-model the measured H{\alpha} equivalent-widths (EW) to obtain the sSFR out to z~6 without stellar mass fitting. We find a strongly increasing rest-frame H{\alpha} EW that is flattening off above z~2.5 with average EWs of 300-600A at z~6. The sSFR is increasing proportional to (1+z)^2.4 at z<2.2 and (1+z)^1.5 at higher redshifts, indicative of a fast mass build-up in high-z galaxies within e-folding times of 100-200Myr at z~6. The redshift evolution at z>3 cannot be fully explained in a picture of cold accretion driven growth. We find a progressively increasing [OIII]{\lambda}5007/H{\beta} ratio out to z~6, consistent with the ratios in local galaxies selected by increasing H{\alpha} EW (i.e., sSFR). This demonstrates the potential of using "local high-z analogs" to investigate the spectroscopic properties and relations of galaxies in the re-ionization epoch.Comment: 18 pages, 11 figures, 3 table

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

Trapping microparticles in a structured dark focus

We experimentally demonstrate stable trapping and controlled manipulation of silica microspheres in a structured optical beam consisting of a dark focus surrounded by light in all directions - the so-called Dark Focus Tweezer. Results from power spectrum and potential analysis demonstrate the non-harmonicity of the trapping potential landspace, which is reconstructed from experimental data in agreement to Lorentz-Mie numerical simulations. Applications of the dark tweezer in levitated optomechanics and biophysics are discussed.Comment: Final versio

The Subaru COSMOS 20: Subaru Optical Imaging of the HST COSMOS Field with 20 Filters

We present both the observations and the data reduction procedures of the Subaru COSMOS 20 project that is an optical imaging survey of the HST COSMOS field, carried out by using Suprime-Cam on the Subaru Telescope with the following 20 optical filters: 6 broad-band (B, g', V, r', i', and z'), 2 narrow-band (NB711 and NB816), and 12 intermediate-band filters (IA427, IA464, IA484, IA505, IA527, IA574, IA624, IA679, IA709, IA738, IA767, and IA827). A part of this project is described in Taniguchi et al. (2007) and Capak et al. (2007) for the six broad-band and one narrow-band (NB816) filter data. In this paper, we present details of the observations and data reduction for remaining 13 filters (the 12 IA filters and NB711). In particular, we describe the accuracy of both photometry and astrometry in all the filter bands. We also present optical properties of the Suprime-Cam IA filter system in Appendix.Comment: 15 pages, 8 figures, 7 tables; accepted for publication in PASJ on October 2, 201

Discovery of a rich proto-cluster at z=2.9 and associated diffuse cold gas in the VIMOS Ultra-Deep Survey (VUDS)

[Abridged] 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 AGNs or radio galaxies, so it is an ideal laboratory to study galaxy formation in dense environments. The structure comprises 12 galaxies with secure spectroscopic redshift in an area of 7'x8', in a z bin of Dz=0.016. The measured galaxy number overdensity is delta_g=12+/-2. This overdensity has total mass of M~8.1x10^(14)M_sun in a volume of 13x15x17 Mpc^3. Simulations indicate that such an overdensity at z~2.9 is a proto-cluster that will collapse in a cluster of total mass M~2.5x10^(15)M_sun at z=0. We compare the properties of the galaxies within the overdensity with a control sample at the same z but outside the overdensity. We did not find any statistically significant difference between the properties (stellar mass, SFR, sSFR, NUV-r, r-K) of the galaxies inside and outside the overdensity. The stacked spectrum of galaxies in the overdensity background shows a significant absorption feature at the wavelength of Lya redshifted at z=2.895 (lambda=4736 A), with a rest frame EW = 4+/- 1.4 A. 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 A, with a detection S/N of ~4. These EW values imply a high column density (N(HI)~3-20x10^(19)cm^(-2)), consistent with a scenario where such absorption is due to intervening cold gas streams, falling into the halo potential wells of the proto-cluster galaxies. However, we cannot exclude the hypothesis that this absorption is due to the diffuse gas within the overdensity.Comment: 15 pages, 9 figures, accepted for publication in A&A (revised version after referee's comments and language editing

The VIMOS VLT Deep Survey final data release: a spectroscopic sample of 35016 galaxies and AGN out to z~6.7 selected with 17.5<=i_{AB}<=24.7

We describe the completed VIMOS VLT Deep Survey, and the final data release of 35016 galaxies and type-I AGN with measured spectroscopic redshifts up to redshift z~6.7, in areas 0.142 to 8.7 square degrees, and volumes from 0.5x10^6 to 2x10^7h^-3Mpc^3. We have selected samples of galaxies based solely on their i-band magnitude reaching i_{AB}=24.75. Spectra have been obtained with VIMOS on the ESO-VLT, integrating 0.75h, 4.5h and 18h for the Wide, Deep, and Ultra-Deep nested surveys. A total of 1263 galaxies have been re-observed independently within the VVDS, and from the VIPERS and MASSIV surveys. They are used to establish the redshift measurements reliability, to assess completeness, and to provide a weighting scheme taking into account the survey selection function. We describe the main properties of the VVDS samples, and the VVDS is compared to other spectroscopic surveys. In total we have obtained spectroscopic redshifts for 34594 galaxies, 422 type-I AGN, and 12430 Galactic stars. The survey has enabled to identify galaxies up to very high redshifts with 4669 redshifts in 1<=z_{spec}<=2, 561 in 2<=z_{spec}<=3 and 468 with z_{spec}>3, and specific populations like LAE have been 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. The VVDS provides a comprehensive survey of the distant universe, covering all epochs since z, or more than 12 Gyr of cosmic time, with a uniform selection, 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 their distribution in space, over this large cosmic time. A final public release of the complete VVDS spectroscopic redshift sample is available at http://cesam.lam.fr/vvds.Comment: Submitted 30 June 2013, Accepted 22 August 2013. Updated with published versio

The VIMOS Ultra-Deep Survey (VUDS): fast increase of the fraction of strong Lyman alpha emitters from z=2 to z=6

Aims. The aim of this work is to constrain the evolution of the fraction of Lya emitters among UV selected star forming galaxies at 2<z<6, and to measure the stellar escape fraction of Lya photons over the same redshift range. Methods. We exploit the ultradeep spectroscopic observations collected by the VIMOS Ultra Deep Survey (VUDS) to build an unique, complete and unbiased sample of 4000 spectroscopically confirmed star forming galaxies at 2<z<6. Our galaxy sample UV luminosities brighter than M* at 2<z<6, and luminosities down to one magnitude fainter than M* at 2<z<3.5. Results. We find that 80% of the star forming galaxies in our sample have EW0(Lya)<10A, and correspondingly fesc(Lya)<1%. By comparing these results with literature, we conclude that the bulk of the Lya luminosity at 2<z<6 comes from galaxies that are fainter in the UV than those we sample in this work. The strong Lya emitters constitute, at each redshift, the tail of the distribution of the galaxies with extreme EW0(Lya) and fesc(Lya) . This tail of large EW0 and fesc(Lya) becomes more important as the redshift increases, and causes the fraction of Lya with EW0> 25A to increase from 5% at z=2 to 30% at z=6, with the increase being relatively stronger beyond z=4. We observe no difference, for the narrow range of UV luminosities explored in this work, between the fraction of strong Lya emitters among galaxies fainter or brighter than M*, although the fraction for the FUV faint galaxies evolves faster, at 2<z<3.5, than for the bright ones. We do observe an anticorrelation between E(B-V) and fesc(Lya): generally galaxies with high fesc(Lya) have also small amounts of dust (and viceversa). However, when the dust content is low (E(B-V)<0.05) we observe a very broad range of fesc(Lya), ranging from 10^-3 to 1. This implies that the dust alone is not the only regulator of the amount of escaping Lya photons.Comment: 12 pages, 6 figures, A&A in pres

Discovering extremely compact and metal-poor, star-forming dwarf galaxies out to z ~ 0.9 in the VIMOS Ultra-Deep Survey

We report the discovery of 31 low-luminosity (-14.5 > M_{AB}(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[OIII] < 1700 A) as part of the VIMOS Ultra Deep Survey (VUDS). VIMOS optical spectra of unprecedented sensitivity ($I_{AB}$ ~ 25 mag) along with multiwavelength photometry and HST imaging are used to investigate spectrophotometric properties of this unique sample and explore, for the first time, the very low stellar mass end (M* < 10^8 M$_{\odot}$) 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 (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 T_e-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, including at least three EELGs showing HeII 4686A emission and four EELGs of extremely metal-poor (<10% solar) galaxies. The LZR and MZR followed by 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 evidences 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.Comment: Letter in A&A 568, L8 (2014). This replacement matches the published versio