The Vimos VLT deep survey Garilli, B.; Le Fèvre, O.; Guzzo, L. ...
Astronomy and astrophysics (Berlin),
08/2008, Letnik:
486, Številka:
3
Journal Article
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Context. The VVDS-Wide survey has been designed to trace the large-scale distribution of galaxies at z similar to 1 on comoving scales reaching similar to 100 h super(-1) Mpc, while providing a good ...control of cosmic variance over areas as large as a few square degrees. This is achieved by measuring redshifts with VIMOS at the ESO VLT to a limiting magnitude I AB = 22.5, targeting four independent fields with sizes of up to 4 deg super(2) each. Aims. We discuss the survey strategy which covers 8.6 deg super(2) and present the general properties of the current redshift sample. This includes 32 734 spectra in the four regions, covering a total area of 6.1 deg super(2) with a sampling rate of 22 to 24%. This paper accompanies the public release of the first 18 143 redshifts of the VVDS-Wide survey from the 4 deg super(2) contiguous area of the F22 field at RA = 22\rm phi . Methods. We have devised and tested an objective method to assess the quality of each spectrum, providing a compact figure-of-merit. This is particularly effective in the case of long-lasting spectroscopic surveys with varying observing conditions. Our figure of merit is a measure of the robustness of the redshift measurement and, most importantly, can be used to select galaxies with uniform high-quality spectra to carry out reliable measurements of spectral features. We also use the data available over the four independent regions to directly measure the variance in galaxy counts. We compare it with general predictions from the observed galaxy two-point correlation function at different redshifts and with that measured in mock galaxy surveys built from the Millennium simulation. Results. The purely magnitude-limited VVDS Wide sample includes 19 977 galaxies, 304 type I AGNs, and 9913 stars. The redshift success rate is above 90% independent of magnitude. A cone diagram of the galaxy spatial distribution provides us with the current largest overview of large-scale structure up to z similar to 1, showing a rich texture of over- and under-dense regions. We give the mean N (z) distribution averaged over 6.1 deg super(2) for a sample limited in magnitude to I AB = 22.5. Comparing galaxy densities from the four fields shows that in a redshift bin Delta z = 0.1 at z similar to 1 one still has factor-of-two variations over areas as large as similar to 0.25 deg super(2). This level of cosmic variance agrees with that obtained by integrating the galaxy two-point correlation function estimated from the F22 field alone. It is also in fairly good statistical agreement with that predicted by the Millennium simulations. Conclusions. The VVDS WIDE survey currently provides the largest area coverage among redshift surveys reaching z similar to 1. The variance estimated over the survey fields shows explicitly how clustering results from deep surveys of even 1 deg super(2) size should be interpreted with caution. The survey data represent a rich data base to select complete sub-samples of high-quality spectra and to study galaxy ensemble properties and galaxy clustering over unprecedented scales at these redshifts. The redshift catalog of the 4 deg super(2) F22 field is publicly available at http://cencosw.oamp.fr.
We derive the mass-metallicity relation of star-forming galaxies up to $z\sim0.9$, using data from the VIMOS VLT Deep Survey. Automatic measurement of emission-line fluxes and equivalent widths have ...been performed on the full spectroscopic sample. This sample is divided into two sub-samples depending on the apparent magnitude selection: wide ($I_{\mathrm{AB}}<22.5$) and deep $I_{\mathrm{AB}}<24$). These two samples span two different ranges of stellar masses. Emission-line galaxies have been separated into star-forming galaxies and active galactic nuclei using emission line ratios. For the star-forming galaxies the emission line ratios have also been used to estimate gas-phase oxygen abundance, using empirical calibrations renormalized in order to give consistent results at low and high redshifts. The stellar masses have been estimated by fitting the whole spectral energy distributions with a set of stellar population synthesis models. We assume at first order that the shape of the mass-metallicity relation remains constant with redshift. Then we find a stronger metallicity evolution in the wide sample as compared to the deep sample. We thus conclude that the mass-metallicity relation is flatter at higher redshift. The observed flattening of the mass-metallicity relation at high redshift is analyzed as an evidence in favor of the open-closed model.
Aims. We present a catalog of 213 type-2 AGN selected from the zCOSMOS survey. The selected sample covers a wide redshift range (0.15 < z < 0.92) and is deeper than any other previous study, ...encompassing the luminosity range $10^{5.5}$ $L_{\odot}$ < $L_{\rm OIII}$ < $10^{9.1}$ $L_{\odot}$. We explore the intrinsic properties of these AGN and the relation to their X-ray emission (derived from the XMM-COSMOS observations). We study their evolution by computing the O iiiλ5007$~\AA$ line luminosity function (LF) and we constrain the fraction of obscured AGN as a function of luminosity and redshift. Methods. The sample was selected on the basis of the optical emission line ratios, after applying a cut to the signal-to-noise ratio (S/N) of the relevant lines. We used the standard diagnostic diagrams (O iii/H${\beta}$ versus N ii/H${\alpha}$ and O iii/H${\beta}$ versus S ii/H${\alpha}$) to isolate AGN in the redshift range 0.15 < z < 0.45 and the diagnostic diagram O iii/H${\beta}$ versus O ii/H${\beta}$ to extend the selection to higher redshift (0.5 < z < 0.92). Results. Combining our sample with one drawn from SDSS, we found that the best description of the evolution of type-2 AGN is a luminosity-dependent density evolution model. Moreover, using the type-1 AGN LF we were able to constrain the fraction of type-2 AGN to the total (type-1 + type-2) AGN population. We found that the type-2 fraction decreases with luminosity, in agreement with the most recent results, and shows signs of a slight increase with redshift. However, the trend with luminosity is visible only after combining the SDSS+zCOSMOS samples. From the COSMOS data points alone, the type-2 fraction seems to be quite constant with luminosity.
Context. Counting clusters is one of the methods to constrain cosmological parameters, but has been limited up to now both by the redshift range and by the relatively small sizes of the homogeneously ...surveyed areas. Aims. In order to enlarge publicly available optical cluster catalogs, in particular at high redshift, we have performed a systematic search for clusters of galaxies in the Canada France Hawaii Telescope Legacy Survey (CFHTLS). Methods. We considered the deep 2, 3 and 4 CFHTLS Deep fields (each 1 $\times$ 1 deg2), as well as the wide 1, 3 and 4 CFHTLS Wide fields. We used the Le Phare photometric redshifts for the galaxies detected in these fields with magnitude limits of i'=25 and 23 for the Deep and Wide fields respectively. We then constructed galaxy density maps in photometric redshift bins of 0.1 based on an adaptive kernel technique and detected structures with SExtractor at various detection levels. In order to assess the validity of our cluster detection rates, we applied a similar procedure to galaxies in Millennium simulations. We measured the correlation function of our cluster candidates. We analyzed large scale properties and substructures, including filaments, by applying a minimal spanning tree algorithm both to our data and to the Millennium simulations. Results. We detected 1200 candidate clusters with various masses (minimal masses between 1.0 $\times$ 1013 and 5.5 $\times$ 1013 and mean masses between 1.3 $\times$ 1014 and 12.6 $\times$ 10$^{14}~M_\odot$) in the CFHTLS Deep and Wide fields, thus notably increasing the number of known high redshift cluster candidates. We found a correlation function for these objects comparable to that obtained for high redshift cluster surveys. We also show that the CFHTLS deep survey is able to trace the large scale structure of the universe up to $z \geq 1$. Our detections are fully consistent with those made in various CFHTLS analyses with other methods. We now need accurate mass determinations of these structures to constrain cosmological parameters. Conclusions. We have shown that a search for galaxy clusters based on density maps built from galaxy catalogs in photometric redshift bins is successful and gives results comparable to or better than those obtained with other methods. By applying this technique to the CFHTLS survey we have increased the number of known optical high redshift cluster candidates by a large factor, an important step towards using cluster counts to measure cosmological parameters.
Aims. We present a homogeneous and complete catalogue of optical galaxy groups identified in the purely flux-limited (17.5 ≤ IAB ≤ 24.0) VIMOS-VLT deep redshift Survey (VVDS). Methods. We use mock ...catalogues extracted from the Millennium Simulation, to correct for potential systematics that might affect the overall distribution as well as the individual properties of the identified systems. Simulated samples allow us to forecast the number and properties of groups that can be potentially found in a survey with VVDS-like selection functions. We use them to correct for the expected incompleteness and, to asses in addition, how well galaxy redshifts trace the line-of-sight velocity dispersion of the underlying mass overdensity. In particular, on these mock catalogues we train the adopted group-finding technique i.e., the Voronoi-Delaunay Method (VDM). The goal is to fine-tune its free parameters, recover in a robust and unbiased way the redshift and velocity dispersion distributions of groups (n(z) and n(σ), respectively), and maximize, at the same time, the level of completeness and purity of the group catalogue. Results. We identify 318 VVDS groups with at least 2 members in the range 0.2 ≤ z ≤ 1.0, among which 144 (/30) with at least 3 (/5) members. The sample has an overall completeness of ~60% and a purity of ~50%. Nearly 45% of the groups with at least 3 members are still recovered if we run the algorithm with a particular parameter set that maximizes the purity (~75%) of the resulting catalogue. We use the group sample to explore the redshift evolution of the fraction fb of blue galaxies (U–B ≤ 1) in the redshift range 0.2 ≤ z ≤ 1. We find that the fraction of blue galaxies is significantly lower in groups than in the global population (i.e. in the whole ensemble of galaxies irrespective of their environment). Both of these quantities increase with redshift, the fraction of blue galaxies in groups exhibiting a marginally significant steeper increase. We also investigate the dependence of fb on group richness: not only we confirm that, at any redshift, the blue fraction decreases in systems with increasing richness, but we find that this result continues to hold towards fainter luminosities.
The PEACH project (Projet en Electricité Atmosphérique pour la Campagne HyMeX – the Atmospheric Electricity Project of the HyMeX Program) is the atmospheric electricity component of the Hydrology ...cycle in the Mediterranean Experiment (HyMeX) experiment and is dedicated to the observation of both lightning activity and electrical state of continental and maritime thunderstorms in the area of the Mediterranean Sea. During the HyMeX SOP1 (Special Observation Period) from 5 September to 6 November 2012, four European operational lightning locating systems (ATDnet, EUCLID, LINET, ZEUS) and the HyMeX lightning mapping array network (HyLMA) were used to locate and characterize the lightning activity over the northwestern Mediterranean at flash, storm and regional scales. Additional research instruments like slow antennas, video cameras, microbarometer and microphone arrays were also operated. All these observations in conjunction with operational/research ground-based and airborne radars, rain gauges and in situ microphysical records are aimed at characterizing and understanding electrically active and highly precipitating events over southeastern France that often lead to severe flash floods. Simulations performed with cloud resolving models like Meso-NH and Weather Research and Forecasting are used to interpret the results and to investigate further the links between dynamics, microphysics, electrification and lightning occurrence. Herein we present an overview of the PEACH project and its different instruments. Examples are discussed to illustrate the comprehensive and unique lightning data set, from radio frequency to acoustics, collected during the SOP1 for lightning phenomenology understanding, instrumentation validation, storm characterization and modeling.
The VLA-VIRMOS Deep Field Bondi, M.; Ciliegi, P.; Zamorani, G. ...
Astronomy and astrophysics (Berlin),
06/2003, Letnik:
403, Številka:
3
Journal Article
Aims. We present a measurement of the dependence of galaxy clustering on galaxy stellar mass at redshift z\sim0.9, based on the first-epoch data from the VVDS-Deep survey. Methods. Concentrating on ...the redshift interval 0.5< z <1.2, we measured the projected correlation function, w_{\rm p}(r_{\rm p}), within mass-selected sub-samples covering the range similar to 10 super(9) and similar to 10 similar to M_\odot. We explored and quantify in detail the observational selection biases due to the flux-limited nature of the survey, both from the data themselves and with a suite of realistic mock samples constructed by coupling the Millennium Simulation to semi-analytic models. We identify the range of masses within which our main conclusions are robust against these effects. Serious incompleteness in mass is present below log\,(M/M_\odot) =9.5, with about two thirds of the galaxies in the range 9<\log\,(M/M_\odot) <9.5 that are lost due to their low luminosity and high mass-to-light ratio. However, the sample is expected to be 100% complete in mass above log\,(M/M_\odot) =10. Results. We present the first direct evidence for a dependence of clustering on the galaxy stellar mass at a redshift as high as z\sim0.85. We quantify this by fitting the projected function w_{\rm p}(r_{\rm p}) with a power-law model. The clustering length increases from r sub(0) =2.76 sub(-0.15) super(+0.17) h super(-1) Mpc for galaxies with mass 10 {9} similar to M_\odot$--> M>10 {9} similar to M_\odot to r sub(0) =4.28 sub(-0.45) super(+0.43) h super(-1) Mpc when only the most massive (10 similar to M_\odot$--> M>10 similar to M_\odot) are considered. At the same time, we observe a significant increase in the slope, which over the same range of masses, changes from gamma=1.67_to gamma=2.28_. Comparison to the SDSS measurements at z\sim0.15 shows that the evolution of w_{\rm p}(r_{\rm p}) is significant for samples of galaxies with M<10 similar to M_\odot, while it is negligible for more massive objects. Considering the growth of structure, this implies that the linear bias b_{\rm L} of the most massive galaxies evolves more rapidly between these two cosmic epochs. We quantify this effect by computing the value of b_{\rm L} from the SDSS and VVDS clustering amplitudes and find that b_{\rm L} decreases from 1.5\pm0.2 at z\sim0.85 to 1.33\pm0.03 at z\sim0.15, for the most massive galaxies, while it remains virtually constant (b_{\rm L}\sim1.3) for the remaining population. Qualitatively, this is the kind of scenario expected for the clustering of dark-matter halos as a function of their total mass and redshift. Our result therefore seems to indicate that galaxies with the highest stellar mass today were originally central objects of the most massive dark-matter halos at earlier times, whose distribution was strongly biased with respect to the overall mass density field.
Aims. In this paper we discuss the mix of star-forming and passive galaxies up to z similar to 2, based on the first epoch VIMOS-VLT Deep Survey (VVDS) data. Methods. We compute rest-frame magnitudes ...and colors and analyse the color-magnitude relation and the color distributions. We also use the multi-band VVDS photometric data and spectral templates fitting to derive multi-color galaxy types. Using our spectroscopic dataset we separate galaxies based on a star-formation activity indicator derived combining the equivalent width of the OII emission line and the strength of the D sub( )n(4000) continuum break. Results. In agreement with previous works we find that the global galaxy rest-frame color distribution follows a bimodal distribution at z \le 1, and we establish that this bimodality holds up to at least z =1.5. The details of the rest-frame color distribution depend however on redshift and on galaxy luminosity, with faint galaxies being bluer than the luminous ones over the whole redshift range covered by our data, and with galaxies becoming bluer as redshift increases. This latter blueing trend does not depend, to a first approximation, on galaxy luminosity. The comparison between the spectral classification and the rest-frame colors shows that about 35-40% of the red objects are in fact star forming galaxies. Hence we conclude that the red sequence cannot be used to effectively isolate a sample of purely passively evolving objects within a cosmological survey. We show how multi-color galaxy types have a slightly higher efficiency than rest-frame color in isolating the passive, non star- forming galaxies within the VVDS sample. Connected to these results is also the finding that the color-magnitude relations derived for the color and for the spectroscopically selected early-type galaxies have remarkably similar properties, with the contaminating star-forming galaxies within the red sequence objects introducing no significant offset in the rest frame colors. Therefore the average color of the red objects does not appear to be a very sensitive indicator for measuring the evolution of the early-type galaxy population.
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