The strategic turn of Organic Farming in Europe : a resource based approach of Organic Marketing Initiatives

International audienceThis paper explores the Organic farming " s development potential in Europe by analysing the enterprises capacities to reach a workable structure of the supply chains, in order to market good products at reasonable prices. This study has been carried out in the framework of the OMIaRD project, which aimed to assess the impact of the Organic Marketing Initiatives on Rural Development. The results show that, after a growing phase, most of the OMIs meet strategic problems linked to their ability to face an increasing of collected, processed and marketed volumes. This strategic turn point leads them to take decisions together with their stakeholders, so as the economical and ethical goals are not questioned by the changes to be implemented

Absorbing boundary conditions for the Westervelt equation

The focus of this work is on the construction of a family of nonlinear absorbing boundary conditions for the Westervelt equation in one and two space dimensions. The principal ingredient used in the design of such conditions is pseudo-differential calculus. This approach enables to develop high order boundary conditions in a consistent way which are typically more accurate than their low order analogs. Under the hypothesis of small initial data, we establish local well-posedness for the Westervelt equation with the absorbing boundary conditions. The performed numerical experiments illustrate the efficiency of the proposed boundary conditions for different regimes of wave propagation

The evolution of galaxy star formation activity in massive halos

There is now a large consensus that the current epoch of the Cosmic Star Formation History (CSFH) is dominated by low mass galaxies while the most active phase at 1<z<2 is dominated by more massive galaxies, which undergo a faster evolution. Massive galaxies tend to inhabit very massive halos such as galaxy groups and clusters. We aim to understand whether the observed "galaxy downsizing" could be interpreted as a "halo downsizing", whereas the most massive halos, and their galaxy populations, evolve more rapidly than the halos of lower mass. Thus, we study the contribution to the CSFH of galaxies inhabiting group-sized halos. This is done through the study of the evolution of the Infra-Red (IR) luminosity function of group galaxies from redshift 0 to ~1.6. We use a sample of 39 X-ray selected groups in the Extended Chandra Deep Field South (ECDFS), the Chandra Deep Field North (CDFN), and the COSMOS field, where the deepest available mid- and far-IR surveys have been conducted with Spitzer MIPS and Hersche PACS. Groups at low redshift lack the brightest, rarest, and most star forming IR-emitting galaxies observed in the field. Their IR-emitting galaxies contribute <10% of the comoving volume density of the whole IR galaxy population in the local Universe. At redshift >~1, the most IR-luminous galaxies (LIRGs and ULIRGs) are preferentially located in groups, and this is consistent with a reversal of the star-formation rate vs .density anti-correlation observed in the nearby Universe. At these redshifts, group galaxies contribute 60-80% of the CSFH, i.e. much more than at lower redshifts. Below z~1, the comoving number and SFR densities of IR-emitting galaxies in groups decline significantly faster than those of all IR-emitting galaxies. Our results are consistent with a "halo downsizing" scenario and highlight the significant role of "environment" quenching in shaping the CSFH.Comment: 14 pages, 10 figures, accepted for publication by A&

A Multiwavelength Consensus on the Main Sequence of Star-Forming Galaxies at z~2

We compare various star formation rate (SFR) indicators for star-forming galaxies at $1.4<z<2.5$ in the COSMOS field. The main focus is on the SFRs from the far-IR (PACS-Herschel data) with those from the ultraviolet, for galaxies selected according to the BzK criterion. FIR-selected samples lead to a vastly different slope of the SFR-stellar mass ($M_*$) relation, compared to that of the dominant main sequence population as measured from the UV, since the FIR selection picks predominantly only a minority of outliers. However, there is overall agreement between the main sequences derived with the two SFR indicators, when stacking on the PACS maps the BzK-selected galaxies. The resulting logarithmic slope of the SFR-{$M_*$} relation is $\sim0.8-0.9$, in agreement with that derived from the dust-corrected UV-luminosity. Exploiting deeper 24$\mu$m-Spitzer data we have characterized a sub-sample of galaxies with reddening and SFRs poorly constrained, as they are very faint in the $B$ band. The combination of Herschel with Spitzer data have allowed us to largely break the age/reddening degeneracy for these intriguing sources, by distinguishing whether a galaxy is very red in B-z because of being heavily dust reddened, or whether because star formation has been (or is being) quenched. Finally, we have compared our SFR(UV) to the SFRs derived by stacking the radio data and to those derived from the H$\alpha$ luminosity of a sample of star-forming galaxies at $1.4<z<1.7$. The two sets of SFRs are broadly consistent as they are with the SFRs derived from the UV and by stacking the corresponding PACS data in various mass bins.Comment: Accepted for publication in MNRA

Intercomparison of Permittivity Measurement Techniques for Ferroelectric Thin Layers

International audienceThe dielectric properties of a KTa0.65Nb0.35O3 (KTN) ferroelectric composition for a submicronic thin layer were measured in the microwave domain using different electromagnetic characterization methods. Complementary experimental techniques (broadband methods versus resonant techniques, waveguide versus transmission line) and complementary data processing procedures (quasi-static theoretical approaches versus full-wave analysis) were selected to investigate the best way to characterize ferroelectric thin films. The measured data obtained from the cylindrical resonant cavity method, the experimental method that showed the least sources of uncertainty, were taken as reference values for comparisons with results obtained using broadband techniques. The error analysis on the methods used is discussed with regard to the respective domains of validity for each method; this enabled us to identify the best experimental approach for obtaining an accurate determination of the microwave dielectric properties of ferroelectric thin layers

zCOSMOS 20k: Satellite galaxies are the main drivers of environmental effects in the galaxy population at least to z~0.7

We explore the role of environment in the evolution of galaxies over 0.1<z<0.7 using the final zCOSMOS-bright data set. Using the red fraction of galaxies as a proxy for the quenched population, we find that the fraction of red galaxies increases with the environmental overdensity and with the stellar mass, consistent with previous works. As at lower redshift, the red fraction appears to be separable in mass and environment, suggesting the action of two processes: mass and environmental quenching. The parameters describing these appear to be essentially the same at z~0.7 as locally. We explore the relation between red fraction, mass and environment also for the central and satellite galaxies separately, paying close attention to the effects of impurities in the central-satellite classification and using carefully constructed samples matched in stellar mass. There is little evidence for a dependence of the red fraction of centrals on overdensity. Satellites are consistently redder at all overdensities, and the satellite quenching efficiency increases with overdensity at 0.1<z<0.4. This is less marked at higher redshift, but both are nevertheless consistent with the equivalent local measurements. At a given stellar mass, the fraction of galaxies that are satellites also increases with the overdensity. At a given overdensity and mass, the obtained relation between the environmental quenching and the satellite fraction agrees well with the satellite quenching efficiency, demonstrating that the environmental quenching in the overall population is consistent with being entirely produced through the satellite quenching process at least up to z=0.7. However, despite the unprecedented size of our high redshift samples, the associated statistical uncertainties are still significant and our statements should be understood as approximations to physical reality, rather than physically exact formulae.Comment: 22 pages, 19 figures, submitted to MNRA

Planck's Dusty GEMS: Gravitationally lensed high-redshift galaxies discovered with the Planck survey

We present an analysis of 11 bright far-IR/submm sources discovered through a combination of the Planck survey and follow-up Herschel-SPIRE imaging. Each source has a redshift z=2.2-3.6 obtained through a blind redshift search with EMIR at the IRAM 30-m telescope. Interferometry obtained at IRAM and the SMA, and optical/near-infrared imaging obtained at the CFHT and the VLT reveal morphologies consistent with strongly gravitationally lensed sources. Additional photometry was obtained with JCMT/SCUBA-2 and IRAM/GISMO at 850 um and 2 mm, respectively. All objects are bright, isolated point sources in the 18 arcsec beam of SPIRE at 250 um, with spectral energy distributions peaking either near the 350 um or the 500 um bands of SPIRE, and with apparent far-infrared luminosities of up to 3x10^14 L_sun. Their morphologies and sizes, CO line widths and luminosities, dust temperatures, and far-infrared luminosities provide additional empirical evidence that these are strongly gravitationally lensed high-redshift galaxies. We discuss their dust masses and temperatures, and use additional WISE 22-um photometry and template fitting to rule out a significant contribution of AGN heating to the total infrared luminosity. Six sources are detected in FIRST at 1.4 GHz. Four have flux densities brighter than expected from the local far-infrared-radio correlation, but in the range previously found for high-z submm galaxies, one has a deficit of FIR emission, and 6 are consistent with the local correlation. The global dust-to-gas ratios and star-formation efficiencies of our sources are predominantly in the range expected from massive, metal-rich, intense, high-redshift starbursts. An extensive multi-wavelength follow-up programme is being carried out to further characterize these sources and the intense star-formation within them.Comment: A&A accepte

The lesser role of starbursts for star formation at z=2

Two main modes of star formation are know to control the growth of galaxies: a relatively steady one in disk-like galaxies, defining a tight star formation rate (SFR)-stellar mass sequence, and a starburst mode in outliers to such a sequence which is generally interpreted as driven by merging. Such starburst galaxies are rare but have much higher SFRs, and it is of interest to establish the relative importance of these two modes. PACS/Herschel observations over the whole COSMOS and GOODS-South fields, in conjunction with previous optical/near-IR data, have allowed us to accurately quantify for the first time the relative contribution of the two modes to the global SFR density in the redshift interval 1.5<z<2.5, i.e., at the cosmic peak of the star formation activity. The logarithmic distributions of galaxy SFRs at fixed stellar mass are well described by Gaussians, with starburst galaxies representing only a relatively minor deviation that becomes apparent for SFRs more than 4 times higher than on the main sequence. Such starburst galaxies represent only 2% of mass-selected star forming galaxies and account for only 10% of the cosmic SFR density at z~2. Only when limited to SFR>1000M(sun)/yr, off-sequence sources significantly contribute to the SFR density (46+/-20%). We conclude that merger-driven starbursts play a relatively minor role for the formation of stars in galaxies, whereas they may represent a critical phase towards the quenching of star formation and morphological transformation in galaxies.Comment: Accepted for publication in ApJ Letter

W Hya : molecular inventory by ISO-SWS

Infrared spectroscopy is a powerful tool to probe the inventory of solid state and molecular species in circumstellar ejecta. Here we analyse the infrared spectrum of the Asymptotic Giant Branch star W Hya, obtained by the Short and Long Wavelength Spectrometers on board of the Infrared Satellite Observatory. These spectra show evidence for the presence of amorphous silicates, aluminum oxide, and magnesium-iron oxide grains. We have modelled the spectral energy distribution using laboratory measured optical properties of these compounds and derive a total dust mass loss rate of 3E-10 Msol/yr. We find no satisfactory fit to the 13 micron dust emission feature and the identification of its carrier is still an open issue. We have also modelled the molecular absorption bands due to H2O, OH, CO, CO2, SiO, and SO2 and estimated the excitation temperatures for different bands which range from 300 to 3000K. It is clear that different molecules giving rise to these absorption bands originate from different gas layers. We present and analyse high resolution Fabry-Perot spectra of the three CO2 bands in the 15 micron region. In these data, the bands are resolved into individual Q-lines in emission, which allows the direct determination of the excitation temperature and column density of the emitting gas. This reveals the presence of a warm (about 450K) extended layer of CO2, somewhere between the photosphere and the dust formation zone. The gas in this layer is cooler than the 1000K CO2 gas responsible for the low-resolution absorption bands at 4.25 and 15 micron. The rotational and vibrational excitation temperatures derived from the individual Q-branch lines of CO2 are different (450K and 150K, respectively) so that the CO2 level population is not in LTE.Comment: To appear in Astronomy and Astrophysics A reference is adde