The zCOSMOS 10k-Bright Spectroscopic Sample

We present spectroscopic redshifts of a large sample of galaxies with I_(AB) < 22.5 in the COSMOS field, measured from spectra of 10,644 objects that have been obtained in the first two years of observations in the zCOSMOS-bright redshift survey. These include a statistically complete subset of 10,109 objects. The average accuracy of individual redshifts is 110 km s^(–1), independent of redshift. The reliability of individual redshifts is described by a Confidence Class that has been empirically calibrated through repeat spectroscopic observations of over 600 galaxies. There is very good agreement between spectroscopic and photometric redshifts for the most secure Confidence Classes. For the less secure Confidence Classes, there is a good correspondence between the fraction of objects with a consistent photometric redshift and the spectroscopic repeatability, suggesting that the photometric redshifts can be used to indicate which of the less secure spectroscopic redshifts are likely right and which are probably wrong, and to give an indication of the nature of objects for which we failed to determine a redshift. Using this approach, we can construct a spectroscopic sample that is 99% reliable and which is 88% complete in the sample as a whole, and 95% complete in the redshift range 0.5 < z < 0.8. The luminosity and mass completeness levels of the zCOSMOS-bright sample of galaxies is also discussed

Mass and environment as drivers of galaxy evolution in SDSS and zCOSMOS and the origin of the Schechter function

We explore the inter-relationships between mass, star-formation rate and environment in the SDSS, zCOSMOS and other surveys. The differential effects of mass and environment are completely separable to z ~ 1, indicating that two distinct processes are operating, "mass-quenching" and "environment-quenching". Environment-quenching, at fixed over-density, evidently does not change with epoch to z ~ 1, suggesting that it occurs as large-scale structure develops in the Universe. The observed constancy of the mass-function shape for star-forming galaxies, demands that the mass-quenching of galaxies around and above M*, must be proportional to their star-formation rates at all z < 2. We postulate that this simple mass-quenching law also holds over a much broader range of stellar mass and epoch. These two simple quenching processes, plus some additional quenching due to merging, then naturally produce (a) a quasi-static Schechter mass function for star-forming galaxies with a value of M* that is set by the proportionality between the star-formation and mass-quenching rates, (b) a double Schechter function for passive galaxies with two components: the dominant one is produced by mass-quenching and has exactly the same M* as the star-forming galaxies but an alpha shallower by +1, while the other is produced by environment effects and has the same M* and alpha as the star-forming galaxies, and is larger in high density environments. Subsequent merging of quenched galaxies modifies these predictions somewhat in the denser environments, slightly increasing M* and making alpha more negative. All of these detailed quantitative relationships between the Schechter parameters are indeed seen in the SDSS, lending strong support to our simple empirically-based model. The model naturally produces for passive galaxies the "anti-hierarchical" run of mean ages and alpha-element abundances with mass.Comment: 66 pages, 19 figures, 1 movie, accepted for publication in ApJ. The movie is also available at http://www.exp-astro.phys.ethz.ch/zCOSMOS/MF_simulation_d1_d4.mo

Evolution de l'agrégation des galaxies dans le sondage VIMOS-VLT Deep Survey

The recent surveys of the Universe highlighted the presence of structures in the matter distribution, such as filaments and voids. To study the evolution of the galaxy spatial distribution, it is necessary to know their accurate position in a three dimensional space. This thesis took place within the framework of the VIMOS-VLT Deep Survey (VVDS). Its goal is to measure some 100000 redshifts to study the formation and evolution of the galaxies and large scale structures of the Universe up to z~5. After having made a review of our knowledge of the galaxies distribution, then introduced the VVDS, I present the measurement and the evolution of the real-space two-point correlation function from the first epoch data of the VVDS, the largest sample of 10759 spectra ever acquired up to I_AB=24. I developed a whole set of programs made available to the VVDS consortium to easily measure the clustering length of galaxies in a given redshift range, with its associated errors, correcting the effects of the VVDS observing strategy. This tool enabled to measure the evolution of the real space correlation function of the global galaxies population up to z=2. I then extended this study dividing the full galaxies sample by spectral type and color. Finaly, combining the GALEX data to the VVDS has allowed me to measure the clustering of an ultraviolet-selected sample of galaxies up to z~1. This is the first time that such measurements are carried out on such a so long range of cosmic time. The results presented in this thesis are thus establishing a new reference in the field.Les grands sondages récents de l'Univers ont mis en évidence la présence de structures dans la distribution de la matière, sous forme de filaments et de vides. Pour étudier l'évolution de la distribution spatiale des galaxies, il est nécessaire de connaître leur position précise dans l'espace à trois dimensions. Cette thèse s'est déroulée dans le cadre du sondage profond VIMOS-VLT Deep Survey (VVDS). Son but est de mesurer quelques 100000 redshifts pour étudier la formation et l'évolution des galaxies et des structures à grande échelle de l'Univers jusqu'à z~5. Après avoir fait un état des lieux de la connaissance que nous avons de la distribution des galaxies, puis introduis le sondage VVDS, je présente la mesure et l'évolution de la fonction de corrélation spatiale à deux points à partir des données de la première époque du VVDS, le plus large échantillon (10759 spectres) jamais acquis à I_AB=24. J'ai développé un ensemble de programmes mis à la disposition du consortium VVDS pour mesurer facilement la longueur de corrélation spatiale des galaxies dans un intervalle en redshift donné, avec ses erreurs associées, en corrigeant les effets de la stratégie d'observation du VVDS. Cet outil a permis de mesurer l'évolution de la fonction de corrélation spatiale de la population globale des galaxies jusqu'à z=2. J'ai prolongé cette étude en divisant l'échantillon de galaxies par type spectral et par couleur. Enfin, en combinant les données de GALEX avec celles du VVDS, j'ai pu mesurer l'agrégation de galaxies sélectionnées en ultraviolet jusqu'à z~1. C'est la première fois que de telles mesures sont réalisées sur une si longue plage de temps cosmique. Les résultats présentés dans cette thèse font ainsi office de nouvelles références pour les travaux futurs

Evolution de l'agrégation des galaxies dans le sondage VIMOS-VLT Deep Survey

Cette thèse s'est déroulée dans le cadre du sondage VIMOS-VLT Deep Survey (VVDS). Son but est de mesurer quelques 100000 redshifts pour étudier la formation et l'évolution des galaxies et des structures de l'Univers à grande échelle jusqu'à z~5. Après un état des lieux de notre connaissance de la distribution des galaxies, suivi d'une description du sondage VVDS, je présente la mesure de la fonction de corrélation spatiale à deux points à partir des données de la première époque du VVDS, le plus large échantillon (10759 spectres) jamais acquis à IAB=24. Je présente ainsi les résultats obtenus quant à la distribution de la population globale des galaxies jusqu'à z=2. Cette étude a été prolongée en divisant l'échantillon de galaxies par type spectral et par couleur, puis complétée par la mesure de l'agrégation de galaxies sélectionnées en ultraviolet. Les résultats présentés dans cette thèse font office de nouvelles références pour les travaux futurs.AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Spatial variations of the optical galaxy luminosity functions and red sequences in the Coma cluster: clues to its assembly history

International audienceContext: Clusters of galaxies are believed to be at the intersections of cosmological filaments and to grow by accreting matter from these filaments. Such continuous infall has major consequences not only on clusters, but also on the physics of cluster galaxies. Faint galaxies are particularly interesting as they are very sensitive to environmental effects and may have different behavior from those of bright galaxies. Aims: The aim of this paper is to sample the Coma cluster building history, based on the analysis of galaxy luminosity functions (LFs) and red sequences (RSs) in the color magnitude relation (CMR) down to faint magnitudes, which are privileged tools for this purpose. Methods: The present analysis is based on deep (R&tilde;24), wide (~0.5 deg^2) multiband (BVRI Vega system) images of the Coma cluster obtained with the CFH12K camera at the CFHT. We have derived LFs and CMRs in twenty 10×10 arcmin2 regions and in larger regions. Results: In all photometric bands, we found steeply rising LFs in the north-northeast half of the cluster (due to early-type galaxies at bright magnitudes and due to late-type galaxies at the faint end), and much flatter LFs in the south-southwest region. Although the behavior of the CMR RS is different in these two regions, a good agreement is found in general between the RS computed for faint and for bright galaxies. Conclusions: .All these results can be interpreted consistently in the framework of the building up process that has been proposed. The Northern Coma area is a relatively quiescent region, while the southern area experiences several infalls

Discovery of a z = 6.17 galaxy from CFHT and VLT observations

International audienceWe report the discovery of a galaxy at a redshift z = 6.17 identified from deep narrow band imaging and spectroscopic follow-up in one of the CFHT-VIRMOS deep survey fields at 0226-04. In addition to the existing deep BVRI images of this field, we obtained a very deep narrow band image at 920 nm with the aim of detecting Lyalpha emission at redshift ~ 6.5. Spectroscopic follow-up of some of the candidates selected on the basis of their excess flux in the NB920 filter was performed at the VLT-UT4 with the FORS2 instrument. For one object a strong and asymmetric emission line associated with a strong break in continuum emission is identified as Lyalpha at z = 6.17. This galaxy was selected from its continuum emission in the 920 nm filter and not from its Lyalpha emission, in effect performing a Lyman Break detection at z = 6.17. We estimate a star formation rate of several tens of Msun yr-1 for this object, with a velocity dispersion ~ 400 km s-1. The spectroscopic follow-up of other high z galaxy candidates is on-going

Searching high-z Lyalpha emitters

International audienceHigh-z galaxies beyond redshift ~ 4 are essentially detected from ground based observations through their Lyalpha emission. The anticipated Lyalpha flux of galaxies at redshifts ~ 6 and beyond is a few times 0.1 10-17 ergs.s-1.cm-2 and its detection requires observations in low background conditions, when the observing wavelength is pushed into the near IR domain. We have carried out observations on 4-8 m telescopes to search for high z galaxies at 920 nm, 1060 and 1187 nm, resorting to various techniques: Narrow Band (NB) imaging and multi-slit windows. Observations, data reduction and preliminary results are described

The VIMOS-VLT deep survey. Color bimodality and the mix of galaxy populations up to z ~ 2

International audienceAims: In this paper we discuss the mix of star-forming and passive galaxies up to z ~ 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_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