Sub-millimeter galaxies as progenitors of compact quiescent galaxies

Three billion years after the big bang (at redshift z=2), half of the most massive galaxies were already old, quiescent systems with little to no residual star formation and extremely compact with stellar mass densities at least an order of magnitude larger than in low redshift ellipticals, their descendants. Little is known about how they formed, but their evolved, dense stellar populations suggest formation within intense, compact starbursts 1-2 Gyr earlier (at 3<z<6). Simulations show that gas-rich major mergers can give rise to such starbursts which produce dense remnants. Sub-millimeter selected galaxies (SMGs) are prime examples of intense, gas-rich, starbursts. With a new, representative spectroscopic sample of compact quiescent galaxies at z=2 and a statistically well-understood sample of SMGs, we show that z=3-6 SMGs are consistent with being the progenitors of z=2 quiescent galaxies, matching their formation redshifts and their distributions of sizes, stellar masses and internal velocities. Assuming an evolutionary connection, their space densities also match if the mean duty cycle of SMG starbursts is 42 (+40/-29) Myr (consistent with independent estimates), which indicates that the bulk of stars in these massive galaxies were formed in a major, early surge of star-formation. These results suggests a coherent picture of the formation history of the most massive galaxies in the universe, from their initial burst of violent star-formation through their appearance as high stellar-density galaxy cores and to their ultimate fate as giant ellipticals.Comment: ApJ (in press

The VIPERS Multi-Lambda Survey. I. UV and NIR Observations, multi-color catalogues and photometric redshifts

We present observations collected in the CFHTLS-VIPERS region in the ultraviolet (UV) with the GALEX satellite (far and near UV channels) and the near infrared with the CFHT/WIRCam camera ($K_s$-band) over an area of 22 and 27 deg$^2$, respectively. The depth of the photometry was optimized to measure the physical properties (e.g., SFR, stellar masses) of all the galaxies in the VIPERS spectroscopic survey. The large volume explored by VIPERS will enable a unique investigation of the relationship between the galaxy properties and their environment (density field and cosmic web) at high redshift (0.5 < z < 1.2). In this paper, we present the observations, the data reductions and the build-up of the multi-color catalogues. The CFHTLS-T0007 (gri-{\chi}^2) images are used as reference to detect and measure the $K_s$-band photometry, while the T0007 u-selected sources are used as priors to perform the GALEX photometry based on a dedicated software (EMphot). Our final sample reaches $NUV_{AB}$~25 (at 5{\sigma}) and $K_{AB}$~22 (at 3{\sigma}). The large spectroscopic sample (~51,000 spectroscopic redshifts) allows us to highlight the robustness of our star/galaxy separation, and the reliability of our photometric redshifts with a typical accuracy $\sigma_z \le$ 0.04 and a catastrophic failure rate {\eta} < 2% down to i~23. We present various tests on the $K_s$ band completeness and photometric redshift accuracy by comparing with existing, overlapping deep photometric catalogues. Finally, we discuss the BzK sample of passive and active galaxies at high redshift and the evolution of galaxy morphology in the (NUV-r) vs (r-K_s) diagram at low redshift (z < 0.25) thanks to the high image quality of the CFHTLS. The images, catalogues and photometric redshifts for 1.5 million sources (down to $NUV \le$ 25 or $K_s \le$ 22) are released and available at this URL: http://cesam.lam.fr/vipers-mls/Comment: 14 pages, 16 figures. Accepted for publication in A&A. Version to be publishe

Environment of MAMBO galaxies in the COSMOS field

Submillimeter galaxies (SMG) represent a dust-obscured high-redshift population undergoing massive star formation activity. Their properties and space density have suggested that they may evolve into spheroidal galaxies residing in galaxy clusters. In this paper, we report the discovery of compact (~10"-20") galaxy overdensities centered at the position of three SMGs detected with the Max-Planck Millimeter Bolometer camera (MAMBO) in the COSMOS field. These associations are statistically significant. The photometric redshifts of galaxies in these structures are consistent with their associated SMGs; all of them are between z=1.4-2.5, implying projected physical sizes of ~170 kpc for the overdensities. Our results suggest that about 30% of the radio-identified bright SMGs in that redshift range form in galaxy density peaks in the crucial epoch when most stars formed.Comment: Accepted for publication in ApJ Letter

Relativistic Proton Production During the 14 July 2000 Solar Event: The Case for Multiple Source Mechanisms

Protons accelerated to relativistic energies by transient solar and interplanetary phenomena caused a ground-level cosmic ray enhancement on 14 July 2000, Bastille Day. Near-Earth spacecraft measured the proton flux directly and ground-based observatories measured the secondary responses to higher energy protons. We have modelled the arrival of these relativistic protons at Earth using a technique which deduces the spectrum, arrival direction and anisotropy of the high-energy protons that produce increased responses in neutron monitors. To investigate the acceleration processes involved we have employed theoretical shock and stochastic acceleration spectral forms in our fits to spacecraft and neutron monitor data. During the rising phase of the event (10:45 UT and 10:50 UT) we find that the spectrum between 140 MeV and 4 GeV is best fitted by a shock acceleration spectrum. In contrast, the spectrum at the peak (10:55 UT and 11:00 UT) and in the declining phase (11:40 UT) is best fitted with a stochastic acceleration spectrum. We propose that at least two acceleration processes were responsible for the production of relativistic protons during the Bastille Day solar event: (1) protons were accelerated to relativistic energies by a shock, presumably a coronal mass ejection (CME). (2) protons were also accelerated to relativistic energies by stochastic processes initiated by magnetohydrodynamic (MHD) turbulence.Comment: 38 pages, 9 figures, accepted for publication in the Astrophysical Journal, January, 200

Studying the evolution of large-scale structure with the VIMOS-VLT Deep Survey

The VIMOS-VLT Deep Survey (VVDS) currently offers a unique combination of depth, angular size and number of measured galaxies among surveys of the distant Universe: ~ 11,000 spectra over 0.5 deg2 to I_{AB}=24 (VVDS-Deep), 35,000 spectra over ~ 7 deg2 to I_{AB}=22.5 (VVDS-Wide). The current ``First Epoch'' data from VVDS-Deep already allow investigations of galaxy clustering and its dependence on galaxy properties to be extended to redshifts ~1.2-1.5, in addition to measuring accurately evolution in the properties of galaxies up to z~4. This paper concentrates on the main results obtained so far on galaxy clustering. Overall, L* galaxies at z~ 1.5 show a correlation length r_0=3.6\pm 0.7. As a consequence, the linear galaxy bias at fixed luminosity rises over the same range from the value b~1 measured locally, to b=1.5 +/- 0.1. The interplay of galaxy and structure evolution in producing this observation is discussed in some detail. Galaxy clustering is found to depend on galaxy luminosity also at z~ 1, but luminous galaxies at this redshift show a significantly steeper small-scale correlation function than their z=0 counterparts. Finally, red galaxies remain more clustered than blue galaxies out to similar redshifts, with a nearly constant relative bias among the two classes, b_{rel}~1.4, despite the rather dramatic evolution of the color-density relation over the same redshift range.Comment: 14 pages. Extended, combined version of two invited review papers presented at: 1) XXVIth Astrophysics Moriond Meeting: "From Dark Halos to Light", March 2006, proc. edited by L.Tresse, S. Maurogordato and J. Tran Thanh Van (Editions Frontieres); 2) Vulcano Workshop 2006 "Frontier Objects in Astrophysics and Particle Physics", May 2006, proc. edited by F. Giovannelli & G. Mannocchi, Italian Physical Society (Editrice Compositori, Bologna

Energy-based metrics for arthroscopic skills assessment

Minimally invasive skills assessment methods are essential in developing efficient surgical simulators and implementing consistent skills evaluation. Although numerous methods have been investigated in the literature, there is still a need to further improve the accuracy of surgical skills assessment. Energy expenditure can be an indication of motor skills proficiency. The goals of this study are to develop objective metrics based on energy expenditure, normalize these metrics, and investigate classifying trainees using these metrics. To this end, different forms of energy consisting of mechanical energy and work were considered and their values were divided by the related value of an ideal performance to develop normalized metrics. These metrics were used as inputs for various machine learning algorithms including support vector machines (SVM) and neural networks (NNs) for classification. The accuracy of the combination of the normalized energy-based metrics with these classifiers was evaluated through a leave-one-subject-out cross-validation. The proposed method was validated using 26 subjects at two experience levels (novices and experts) in three arthroscopic tasks. The results showed that there are statistically significant differences between novices and experts for almost all of the normalized energy-based metrics. The accuracy of classification using SVM and NN methods was between 70% and 95% for the various tasks. The results show that the normalized energy-based metrics and their combination with SVM and NN classifiers are capable of providing accurate classification of trainees. The assessment method proposed in this study can enhance surgical training by providing appropriate feedback to trainees about their level of expertise and can be used in the evaluation of proficiency

The XMM-LSS survey: The XMDS/VVDS 4 sigma catalogue

We present a first catalogue of X-ray sources resulting from the central area of the XMM-LSS (Large Scale Structure survey). We describe the reduction procedures and the database tools we developed and used to derive a well defined catalogue of X-ray sources. The present catalogue is limited to a sub-sample of 286 sources detected at 4 sigma in the 1 deg^2 area covered by the photometric VVDS (VIRMOS VLT Deep Survey), which allows us to provide optical and radio identifications. We also discuss the X-ray properties of a larger X-ray sample of 536 sources detected at > 4 sigma in the full 3 deg^2 area of the XMM Medium Deep Survey (XMDS) independently of the optical identification. We also derive the logN-logS relationship for a sample of more than one thousand sources that we discuss in the context of other surveys at similar fluxes.Comment: 15+6 pages, 12 figures, accepted for publication in Astronomy & Astrophysics The online catalogue announced in the paper will be accessible in about 2 weeks due to technical reasons Fig. 2 replaced with a low resolution on

Effect of in-cylinder swirl on engine efficiency and heat rejection in a light-duty diesel engine

[EN] During the last years, the growing awareness about the impacts of climate change lead to an increase in the importance of the efficiency over other criteria in the design of internal combustion engines. In this framework, the heat transfer to the combustion chamber walls can be considered as one of the main sources of indicated efficiency diminution. Hence, the main objective of this research is to thoroughly assess the effect of the swirl ratio on the heat rejection to the chamber walls, and thus on the efficiency, of a fully instrumented four-cylinder direct-injection diesel engine with variable swirl ratio (covering the range from 1.4 to 3). The analysis, based on the engine global energy balance, includes a combination of theoretical and experimental tools such as thermal flow measurement and dedicated thermocouples in the cylinder head and liner. Considering the results, it is shown that an increase in swirl ratio leads to a heat transfer enhancement, along with important changes on the combustion development. As a result of the combination of these two effects, it is shown that intermediate swirl ratios can slightly improve engine efficiency at low load, while increasing swirl worsens the combustion process and efficiency at high load. However, convective heat transfer increases about 3% of the fuel energy in the chamber when swirl ratio increases from 1.4 to 3. The heat rejection characterization is completed with the analysis of the wall temperatures. Despite the observed trends, heat transfer does not seem to be the only key issue for explaining the indicated and brake efficiencies, thus the pumping work plays an important role due to the effect of reducing the intake section to generate the swirl motion.This work was supported by GM Global R&D and the Spanish Ministry of Economy and Competitiveness (TRA2013-41348-R).Olmeda, P.; Martín, J.; Blanco-Cavero, D.; Warey, A.; Domenech, V. (2017). Effect of in-cylinder swirl on engine efficiency and heat rejection in a light-duty diesel engine. International Journal of Engine Research. 18(1-2):81-92. https://doi.org/10.1177/1468087417693078S8192181-

The FMOS-COSMOS survey of star-forming galaxies at z ~ 1.6. I. H\alpha -based star formation rates and dust extinction

We present the first results from a near-IR spectroscopic survey of the COSMOS field, using the Fiber Multi-Object Spectrograph on the Subaru telescope, designed to characterize the star-forming galaxy population at $1.4<z<1.7$. The high-resolution mode is implemented to detect H$\alpha$ in emission between $1.6{\rm -}1.8 \mathrm{\mu m}$ with $f_{\rm H\alpha}\gtrsim4\times10^{-17}$ erg cm$^{-2}$ s$^{-1}$. Here, we specifically focus on 271 sBzK-selected galaxies that yield a H$\alpha$ detection thus providing a redshift and emission line luminosity to establish the relation between star formation rate and stellar mass. With further $J$-band spectroscopy for 89 of these, the level of dust extinction is assessed by measuring the Balmer decrement using co-added spectra. We find that the extinction ($0.6\lesssim A_\mathrm{H\alpha} \lesssim 2.5$) rises with stellar mass and is elevated at high masses compared to low-redshift galaxies. Using this subset of the spectroscopic sample, we further find that the differential extinction between stellar and nebular emission \hbox{$E_\mathrm{star}(B-V)/E_\mathrm{neb}(B-V)$} is 0.7--0.8, dissimilar to that typically seen at low redshift. After correcting for extinction, we derive an H$\alpha$-based main sequence with a slope ($0.81\pm0.04$) and normalization similar to previous studies at these redshifts.Comment: 6 pages, 4 figures, and 1 table. Published in ApJ Letter