Dix ans de mesures de biomasses de zooplancton a la station cotière d'Abidjan: 1969-1979

Graphs of variations of zooplankton biomasses expressed as ash-free dry weight (i.e. organic matter) are presented for the 1969-1979 period. The graph of the average year shows: an enrichment season from mid-July till mid-November in which the biomass is 2.3 times higher than the rest of the year and characterized by a slight decrease of the biomass in late August or early September. The warm season is divided into a period of moderate biomass from November till February, a period of moderate biomass from November till February and a period of steady decline of the biomass till the start of the upwelling at the end of June

On the filamentary environment of galaxies

The correlation between the large-scale distribution of galaxies and their spectroscopic properties at z=1.5 is investigated using the Horizon MareNostrum cosmological run. We have extracted a large sample of 10^5 galaxies from this large hydrodynamical simulation featuring standard galaxy formation physics. Spectral synthesis is applied to these single stellar populations to generate spectra and colours for all galaxies. We use the skeleton as a tracer of the cosmic web and study how our galaxy catalogue depends on the distance to the skeleton. We show that galaxies closer to the skeleton tend to be redder, but that the effect is mostly due to the proximity of large haloes at the nodes of the skeleton, rather than the filaments themselves. This effects translate into a bimodality in the colour distribution of our sample. The origin of this bimodality is investigated and seems to follow from the ram pressure stripping of satellite galaxies within the more massive clusters of the simulation. The virtual catalogues (spectroscopical properties of the MareNostrum galaxies at various redshifts) are available online at http://www.iap.fr/users/pichon/MareNostrum/cataloguesComment: 18 pages, 27 figures, accepted for publication in MNRA

Very High-Redshift Lensed Galaxies

We review in this paper the main results recently obtained on the identification and study of very high-z galaxies usinglensing clusters as natural gravitational telescopes. We present in detail our pilot survey with ISAAC/VLT, aimed at the detection of z>7 sources. Evolutionary synthesis models for extremely metal-poor and PopIII starbursts have been used to derive the observational properties expected for these high-z galaxies, such as expected magnitudes and colors, line fluxes for the main emission lines, etc. These models have allowed to define fairly robust selection criteria to find z~7-10 galaxies based on broad-band near-IR photometry in combination with the traditional Lyman drop-out technique. The first results issued from our photometric and spectroscopic survey are discussed, in particular the preliminary confirmation rate, and the global properties of our high-z candidates, including the latest results on the possible z=10.0 candidate A1835-1916. The search efficiency should be significantly improved by the future near-IR multi-object ground-based and space facilities. However, strong lensing clusters remain a factor of ~5-10 more efficient than blank fields in this redshift domain, within the FOV of a few arcminutes around the cluster core, for the typical depth required for this survey project.Comment: 14 pages, 7 figures, Proceedings of IAU Symposium No. 225: The Impact of Gravitational Lensing on Cosmology, Y. Mellier and G. Meylan, Ed

ISAAC/VLT observations of a lensed galaxy at z=10.0

We report the first likely spectroscopic confirmation of a z 10.0 galaxy from our ongoing search for distant galaxies with ISAAC/VLT. Galaxy candidates at z >~ 7 are selected from ultra-deep JHKs images in the core of gravitational lensing clusters for which deep optical imaging is also available, including HST data. The object reported here, found behind Abell 1835, exhibits a faint emission line detected in the J band, leading to z=10.0 when identified as Ly-a, in excellent agreement with the photometric redshift determination. Redshifts z < 7 are very unlikely for various reasons we discuss. The object is located on the critical lines corresponding to z=9 to 11. The magnification factor \mu ranges from 25 to 100. For this object we estimate SFR(Ly-a) (0.8-2.2) Msun/yr and SFR(UV) (47-75) Msun/yr, both uncorrected for lensing. The steep UV slope indicates a young object with negligible dust extinction. SED fits with young low-metallicity stellar population models yield (adopting mu=25) a lensing corrected stellar mass of M*~8.e+6 Msun, and luminosities of 2.e+10 Lsun, corresponding to a dark matter halo of a mass of typically M_tot>~ 5.e+8 Msun. In general our observations show that under excellent conditions and using strong gravitational lensing direct observations of galaxies close to the ``dark ages'' are feasible with ground-based 8-10m class telescopes.Comment: To be published in A&A, Vol. 416, p. L35. Press release information, additional figures and information available at http://obswww.unige.ch/sfr and http://webast.ast.obs-mip.fr/galaxie

Dwarf Galaxy Clustering and Missing Satellites

At redshifts around 0.1 the CFHT Legacy Survey Deep fields contain some 6x10^4 galaxies spanning the mass range from 10^5 to 10^12 Msun. We measure the stellar mass dependence of the two point correlation using angular measurements to largely bypass the errors, approximately 0.02 in the median, of the photometric redshifts. Inverting the power-law fits with Limber's equation we find that the auto-correlation length increases from a very low 0.4hMpc at 10^5.5 Msun to the conventional 4.5hMpc at 10^10.5 Msun. The power law fit to the correlation function has a slope which increases from gamma approximately 1.6 at high mass to gamma approximately 2.3 at low mass. The spatial cross-correlation of dwarf galaxies with more massive galaxies shows fairly similar trends, with a steeper radial dependence at low mass than predicted in numerical simulations of sub-halos within galaxy halos. To examine the issue of missing satellites we combine the cross-correlation measurements with our estimates of the low mass galaxy number density. We find on the average there are 60+/-20 dwarfs in sub-halos with M(total) > 10^7 Msun for a typical Local Group M(total)/M(stars)=30, corresponding to M/L_V approximately 100 for a galaxy with no recent star formation. The number of dwarfs per galaxy is about a factor of two larger than currently found for the Milky Way. Nevertheless, the average dwarf counts are about a factor of 30 below LCDM simulation results. The divergence from LCDM predictions is one of slope of the relation, approximately dN/dlnM approximately -0.5 rather than the predicted -0.9, not sudden onset at some characteristic scale. The dwarf galaxy star formation rates span the range from passive to bursting, which suggests that there are few completely dark halos.Comment: revised version submitted to Astrophysical Journa

Ultraviolet to infrared emission of z>1 galaxies: Can we derive reliable star formation rates and stellar masses?

We seek to derive star formation rates (SFR) and stellar masses (M_star) in distant galaxies and to quantify the main uncertainties affecting their measurement. We explore the impact of the assumptions made in their derivation with standard calibrations or through a fitting process, as well as the impact of the available data, focusing on the role of IR emission originating from dust. We build a sample of galaxies with z>1, all observed from the UV to the IR (rest frame). The data are fitted with the code CIGALE, which is also used to build and analyse a catalogue of mock galaxies. Models with different SFHs are introduced. We define different set of data, with or without a good sampling of the UV range, NIR, and thermal IR data. The impact of these different cases on the determination of M_star and SFR are analysed. Exponentially decreasing models with a redshift formation of the stellar population z ~8 cannot fit the data correctly. The other models fit the data correctly at the price of unrealistically young ages when the age of the single stellar population is taken to be a free parameter. The best fits are obtained with two stellar populations. As long as one measurement of the dust emission continuum is available, SFR are robustly estimated whatever the chosen model is, including standard recipes. M_star measurement is more subject to uncertainty, depending on the chosen model and the presence of NIR data, with an impact on the SFR-M_star scatter plot. Conversely, when thermal IR data from dust emission are missing, the uncertainty on SFR measurements largely exceeds that of stellar mass. Among all physical properties investigated here, the stellar ages are found to be the most difficult to constrain and this uncertainty acts as a second parameter in SFR measurements and as the most important parameter for M_star measurements.Comment: 14 pages, 14 figures, accepted for publication A&

EROs found behind lensing clusters: II.Empirical properties, classification, and SED modelling based on multi-wavelength observations

We study the properties and nature of extremely red galaxies (ERO, R-K>5.6) found behind two lensing clusters and compare them with other known galaxy populations. New HST/ACS observations, Spitzer IRAC and MIPS, and Chandra/ACIS observations of the two lensing clusters Abell 1835 and AC114 contemplate our earlier optical and near-IR observations and have been used to study extremely red objects (EROs) in these deep fields. We have found 6 and 9 EROs in Abell 1835 and AC114. Several (7) of these objects are undetected up to the I and/or z band, and are hence ``optical'' drop-out sources. The photometric redshifts of most of our sources (80%) are z~0.7-1.5. According to simple colour-colour diagrams the majority of our objects would be classified as hosting old stellar populations. However, there are clear signs of dusty starbursts for several among them. These objects correspond to the most extreme ones in R-K colour. We estimate a surface density of (0.97+-0.31) arcmin-2 for EROs with (R-K>5.6) at K<20.5. Among our 15 EROs 6 (40 %) also classify as distant red galaxies (DRGs). 11 of 13 EROs with available IRAC photometry also fulfil the selection criteria for IRAC selected EROs (IEROs) of Yan et al. (2004). SED modelling shows that ~ 36 % of the IEROs in our sample are luminous or ultra-luminous infrared galaxies ((U)LIRG). Some very red DRGs are found to be very dusty starbursts, even (U)LIRGs, as also supported by their mid-IR photometry. No indication for AGNs is found, although faint activity cannot be excluded for all objects. From mid-IR and X-ray data 5 objects are clearly classified as starbursts. The derived properties are quite similar to those of DRGs and IEROs, except for 5 extreme objects in terms of colours, for which a very high extinction (Av>3) is found.Comment: 20 pages, 10 figures, accepted for publication in A&