Premiers résultats sur l'excrétion et la production du zooplancton de la Lagune Ebrié (Côte d'Ivoire)

Biomass and metabolic rates (total nitrogen and phosphorus excretion and respiration) were measured at 4 stations, representative of the lagoon environment, during high-water (Oct-Nov), dry (Dec-Jan) and rainy (July) seasons. In low-salinity waters (4o/oo) Acartia clausi is almost the only species, whereas a marine and diversified fauna is brought in from the ocean during the dry season. O/NT and O/PT atomic ratios between respiration (O) and total nitrogen (NT) and phosphorus (PT) excretions are high (15.1 and 111, respectively) and show a marked hydrocarbon feeding of zooplankton. Production was assessed from excretion via the net growth efficiency coefficient, K2 , calculated from N/P ratios for particles (a1), zooplankton excretion (a2) and constitution (a3). Daily productivity indices (i.e. daily production/biomass ratio) are high and equivalent to 1.2-3.8 day turn-over times. These high values may be ascribed to high temperatures (26.5-30 C) and phytoplankton richness (surface chlorophyll 'a' concentrations are always greater than 4 mg/m-3). Finally, the paper deals with trophic relationships between phyto- and zooplankton (ingestion /primary production ratio and transfer coefficient) and the question of relationships between zooplankton and predators

Characterizing groundwater flow and heat transport in fractured rock using Fiber-Optic Distributed Temperature Sensing

International audienceWe show how fully distributed space-time measurements with Fiber-Optic Distributed Temperature Sensing (FO-DTS) can be used to investigate groundwater flow and heat transport in fractured media. Heat injection experiments are combined with temperature measurements along fiber-optic cables installed in boreholes. Thermal dilution tests are shown to enable detection of cross-flowing fractures and quantification of the cross flow rate. A cross borehole thermal tracer test is then analyzed to identify fracture zones that are in hydraulic connection between boreholes and to estimate spatially distributed temperature breakthrough in each fracture zone. This provides a significant improvement compared to classical tracer tests, for which concentration data are usually integrated over the whole abstraction borehole. However, despite providing some complementary results, we find that the main contributive fracture for heat transport is different to that for a solute tracer

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

A ring galaxy at z=1 lensed by the cluster Abell 370

We present a study of a very peculiar object found in the field of the cluster-lens Abell 370. This object displays, in HST imaging, a spectacular morphology comparable to nearby ring-galaxies. From spectroscopic observations at the CFHT, we measured a redshift of $z=1.062$ based on the identification of [O ii] 3727 \AA and [Ne v] 3426 \AA emission lines. These emission lines are typical of starburst galaxies hosting a central active nucleus and are in good agreement with the assumption that this object is a ring-galaxy. This object is also detected with ISO in the LW2 and LW3 filters, and the mid Infra-Red (MIR) flux ratio favors a Seyfert 1 type. The shape of the ring is gravitationally distorted by the cluster-lens, and most particularly by a nearby cluster elliptical galaxy. Using the cluster mass model, we can compute its intrinsic shape. Requiring that the outer ring follows an ellipse we put constraints on the M/L ratio of the nearby galaxy and derive a magnification factor of 2.5 $\pm$ 0.2. The absolute luminosities of the source are then $L_B = 1.3 \ 10^{12} L_{B \odot}$and$\nu$L$_\nu \simeq 4. 10^{10}$L$_\odot$ in the mid-IR.Comment: 5 pages, 5 figures, uses aa.cls, accepted to A&A Letters. Minor changes, Figure 1 revisited and typos adde