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Search Results: 1 - 10 of 454705 matches for " Jérémy Blaizot "
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Lyman-α Emitters in the context of hierarchical galaxy formation: predictions for VLT/MUSE surveys
Thibault Garel,Bruno Guiderdoni,Jérémy Blaizot
Physics , 2015, DOI: 10.1093/mnras/stv2467
Abstract: The VLT Multi Unit Spectroscopic Explorer (MUSE) integral-field spectrograph can detect Ly\alpha{} emitters (LAE) in the redshift range $2.8 \lesssim z \lesssim 6.7$ in a homogeneous way. Ongoing MUSE surveys will notably probe faint Ly\alpha{} sources that are usually missed by current narrow-band surveys. We provide quantitative predictions for a typical wedding-cake observing strategy with MUSE based on mock catalogs generated with a semi-analytic model of galaxy formation coupled to numerical Ly\alpha{} radiation transfer models in gas outflows. We expect $\approx$ 1500 bright LAEs ($F_{Ly\alpha}$ $\gtrsim$ $10^{-17}$ erg s$^{-1}$ cm$^{-2}$) in a typical Shallow Field (SF) survey carried over $\approx$ 100 arcmin$^2$, and $\approx$ 2,000 sources as faint as $10^{-18}$ erg s$^{-1}$ cm$^{-2}$ in a Medium-Deep Field (MDF) survey over 10 arcmin$^2$. In a typical Deep Field (DF) survey of 1 arcmin$^2$, we predict that $\approx$ 500 extremely faint LAEs ($F_{Ly\alpha}$ $\gtrsim$ $4 \times 10^{-19}$ erg s$^{-1}$ cm$^{-2}$) will be found. Our results suggest that faint Ly\alpha{} sources contribute significantly to the cosmic Ly\alpha{} luminosity and SFR budget. While the host halos of bright LAEs at z $\approx$ 3 and 6 have descendants with median masses of $2 \times 10^{12}$ and $5 \times 10^{13}$ $M_{\odot}$ respectively, the faintest sources detectable by MUSE at these redshifts are predicted to reside in halos which evolve into typical sub-$L^{*}$ and $L^{*}$ galaxy halos at z = 0. We expect typical DF and MDF surveys to uncover the building blocks of Milky Way-like objects, even probing the bulk of the stellar mass content of LAEs located in their progenitor halos at z $\approx$ 3.
Modelling high redshift Lyman-alpha Emitters
Thibault Garel,Jérémy Blaizot,Bruno Guiderdoni,Daniel Schaerer,Anne Verhamme,Matthew Hayes
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.20607.x
Abstract: We present a new model for high redshift Lyman-Alpha Emitters (LAEs) in the cosmological context which takes into account the resonant scattering of Ly-a photons through expanding gas. The GALICS semi-analytic model provides us with the physical properties of a large sample of high redshift galaxies. We implement a gas outflow model for each galaxy based on simple scaling arguments. The coupling with a library of numerical experiments of Ly-a transfer through expanding or static dusty shells of gas allows us to derive the Ly-a escape fractions and profiles. The predicted distribution of Ly-a photons escape fraction shows that galaxies with a low star formation rate have a f_esc of the order of unity, suggesting that, for those objects, Ly-a may be used to trace the star formation rate assuming a given conversion law. In galaxies forming stars intensely, the escape fraction spans the whole range from 0 to 1. The model is able to get a good match to the UV and Ly-a luminosity function (LF) data at 3 < z < 5. We find that we are in good agreement with both the bright Ly-a data and the faint population observed by Rauch et al. (2008) at z=3. Most of the Ly-a profiles of our LAEs are redshifted by the diffusion in the outflow which suppresses IGM absorption. The bulk of the observed Ly-a equivalent width (EW) distribution is recovered by our model, but we fail to obtain the very large values sometimes detected. Predictions for stellar masses and UV LFs of LAEs show a satisfactory agreement with observational estimates. The UV-brightest galaxies are found to show only low Ly-a EWs in our model, as it is reported by many observations of high redshift LAEs. We interpret this effect as the joint consequence of old stellar populations hosted by UV-bright galaxies, and high HI column densities that we predict for these objects, which quench preferentially resonant Ly-a photons via dust extinction.
Cosmological Simulations on a Grid of Computers
Benjamin Depardon,Eddy Caron,Frédéric Desprez,Jérémy Blaizot,Hélène M. Courtois
Physics , 2010, DOI: 10.1063/1.3462722
Abstract: The work presented in this paper aims at restricting the input parameter values of the semi-analytical model used in GALICS and MOMAF, so as to derive which parameters influence the most the results, e.g., star formation, feedback and halo recycling efficiencies, etc. Our approach is to proceed empirically: we run lots of simulations and derive the correct ranges of values. The computation time needed is so large, that we need to run on a grid of computers. Hence, we model GALICS and MOMAF execution time and output files size, and run the simulation using a grid middleware: DIET. All the complexity of accessing resources, scheduling simulations and managing data is harnessed by DIET and hidden behind a web portal accessible to the users.
LyMAS: Predicting Large-Scale Lyman-alpha Forest Statistics from the Dark Matter Density Field
Sébastien Peirani,David H. Weinberg,Stéphane Colombi,Jérémy Blaizot,Yohan Dubois,Christophe Pichon
Physics , 2013, DOI: 10.1088/0004-637X/784/1/11
Abstract: [abridged] We describe LyMAS (Ly-alpha Mass Association Scheme), a method of predicting clustering statistics in the Ly-alpha forest on large scales from moderate resolution simulations of the dark matter distribution, with calibration from high-resolution hydrodynamic simulations of smaller volumes. We use the "Horizon MareNostrum" simulation, a 50 Mpc/h comoving volume evolved with the adaptive mesh hydrodynamic code RAMSES, to compute the conditional probability distribution P(F_s|delta_s) of the transmitted flux F_s, smoothed (1-dimensionally) over the spectral resolution scale, on the dark matter density contrast delta_s, smoothed (3-dimensionally) over a similar scale. In this study we adopt the spectral resolution of the SDSS-III BOSS at z=2.5, and we find optimal results for a dark matter smoothing length sigma=0.3 Mpc/h (comoving). In extended form, LyMAS exactly reproduces both the 1-dimensional power spectrum and 1-point flux distribution of the hydro simulation spectra. Applied to the MareNostrum dark matter field, LyMAS accurately predicts the 2-point conditional flux distribution and flux correlation function of the full hydro simulation for transverse sightline separations as small as 1 Mpc/h, including redshift-space distortion effects. It is substantially more accurate than a deterministic density-flux mapping ("Fluctuating Gunn-Peterson Approximation"), often used for large volume simulations of the forest. With the MareNostrum calibration, we apply LyMAS to 1024^3 N-body simulations of a 300 Mpc/h and 1.0 Gpc/h cube to produce large, publicly available catalogs of mock BOSS spectra that probe a large comoving volume. LyMAS will be a powerful tool for interpreting 3-d Ly-alpha forest data, thereby transforming measurements from BOSS and other massive quasar absorption surveys into constraints on dark energy, dark matter, space geometry, and IGM physics.
A young star-forming galaxy at z = 3.5 with an extended Ly\,$α$ halo seen with MUSE
Vera Patrício,Johan Richard,Anne Verhamme,Lutz Wisotzki,Jarle Brinchmann,Monica L. Turner,Lise Christensen,Peter M. Weilbacher,Jérémy Blaizot,Roland Bacon,Thierry Contini,David Lagattuta,Sebastiano Cantalupo,Benjamin Clément,Geneviève Soucail
Physics , 2015,
Abstract: Spatially resolved studies of high redshift galaxies, an essential insight into galaxy formation processes, have been mostly limited to stacking or unusually bright objects. We present here the study of a typical (L$^{*}$, M$_\star$ = 6 $\times 10^9$ $M_\odot$) young lensed galaxy at $z=3.5$, observed with MUSE, for which we obtain 2D resolved spatial information of Ly$\alpha$ and, for the first time, of CIII] emission. The exceptional signal-to-noise of the data reveals UV emission and absorption lines rarely seen at these redshifts, allowing us to derive important physical properties (T$_e\sim$15600 K, n$_e\sim$300 cm$^{-3}$, covering fraction f$_c\sim0.4$) using multiple diagnostics. Inferred stellar and gas-phase metallicities point towards a low metallicity object (Z$_{\mathrm{stellar}}$ = $\sim$ 0.07 Z$_\odot$ and Z$_{\mathrm{ISM}}$ $<$ 0.16 Z$_\odot$). The Ly$\alpha$ emission extends over $\sim$10 kpc across the galaxy and presents a very uniform spectral profile, showing only a small velocity shift which is unrelated to the intrinsic kinematics of the nebular emission. The Ly$\alpha$ extension is $\sim$4 times larger than the continuum emission, and makes this object comparable to low-mass LAEs at low redshift, and more compact than the Lyman-break galaxies and Ly$\alpha$ emitters usually studied at high redshift. We model the Ly$\alpha$ line and surface brightness profile using a radiative transfer code in an expanding gas shell, finding that this model provides a good description of both observables.
Stars and statistical physics: a teaching experience
R. Balian,J. -P. Blaizot
Physics , 1999, DOI: 10.1119/1.19105
Abstract: The physics of stars, their workings and their evolution, is a goldmine of problems in statistical mechanics and thermodynamics. We discuss many examples that illustrate the possibility of deepening student's knowledge of statistical mechanics by an introductory study of stars. The matter constituting the various stellar objects provides examples of equations of state for classical or quantal and relativistic or non-relativistic gases. Maximum entropy can be used to characterize thermodynamic and gravitational equilibrium which determines the structure of stars and predicts their instability above a certain mass. Contraction accompanying radiation induces either heating or cooling, which explains the formation of stars above a minimum mass. The characteristics of the emitted light are understood from black-body radiation and more precisely from the Boltzmann-Lorentz kinetic equation for photons. The luminosity is governed by the transport of heat by photons from the center to the surface. Heat production by thermonuclear fusion is determined by microscopic balance equations. The stability of the steady state of stars is controlled by the interplay of thermodynamics and gravitation.
Cyclones and Societies in the Mascarene Islands 17th-20th Centuries  [PDF]
Emmanuel Garnier, Jérémy Desarthe
American Journal of Climate Change (AJCC) , 2013, DOI: 10.4236/ajcc.2013.21001

The recent IPCC-SREX report focuses on the impact of extreme weather events on societies and underlines the absence of reliable data to assert a solid link between them and the current global climate change. Thanks to the unpublished materials that are contained in historic archives, this article suggests studying the cyclones which affected the Mascarene islands between 1654 and 2007 and which supply us with a catalog of hitherto unpublished events. Inspired by the Simpson-Saffir hurricanes Wind Scale, the research proposes a relative evaluation of the extremes of the region. It underlines the big fluctuations in the last three centuries and partially answers the current debate on the reliability of the data in relation to hurricanes and their link with the contemporary climate. The available archives show that this type of meteorological event has occurred frequently during the relevant historical period and that for that reason, has given rise to original strategies of adaptation on the part of the societies affected. The results presented here constitute new and reliable data which could make an important contribution to the decision-makers and to climatologists trying to design strategies which the populations of small islands facing the climatic hazards of the future will have to adopt.

High energy pA collisions in the color glass condensate approach II. Quark production
J. P. Blaizot,F. Gelis,R. Venugopalan
Physics , 2004, DOI: 10.1016/j.nuclphysa.2004.07.006
Abstract: We compute the production of quark-antiquark pairs in high energy collisions between a small and a large projectile, as in proton-nucleus collisions, in the framework of the Color Glass Condensate. We derive a general expression for quark pair-production, which is not k_t-factorizable. However, k_t-factorization is recovered in the limit of large mass pairs or large quark--anti-quark momenta. Our results are amenable to a simple interpretation and suggest how multi-parton correlations at small x can be quantified in high-energy proton/deuteron-nucleus collisions.
High energy pA collisions in the color glass condensate approach I. Gluon production and the Cronin effect
J. P. Blaizot,F. Gelis,R. Venugopalan
Physics , 2004, DOI: 10.1016/j.nuclphysa.2004.07.005
Abstract: We study gluon production in high energy proton-nucleus collisions in the semi-classical framework of the Color Glass Condensate. We develop a general formalism to compute gluon fields in covariant gauge to lowest order in the classical field of the proton and to all orders in the classical field of the nucleus. The use of the covariant gauge makes the diagrammatic interpretation of the solution more transparnt. k_t-factorization holds to this order for gluon production -- Our results for the gluon distribution are equivalent to the prior diagrammatic analysis of Kovchegov and Mueller. We also show that these results are equivalent to the computation of gluon production by Dumitru and McLerran in the Fock-Schwinger gauge. We demonstrate how the Cronin effect arises in this approach, and examine its behavior in the two extreme limits of a) no small-x quantum evolution, and b) fully saturated quantum evolution. In both cases, the formalism reduces to Glauber's formalism of multiple scatterings. We comment on the possible implications of this study for the interpretation of the recent results on Deuteron-Gold collisions at the Relativistic Heavy Ion Collider (RHIC).
Des monts et des mondes: ce que le corps des marcheurs solitaires fait à la sociologie
Jérémy Damian
m@gm@ , 2009,
Abstract: En faisant de l’expérience de la marche solitaire un détour permettant d’éclairer les racines sensibles et la dimension corporelle du vivre-ensemble que la culture moderne refoule et rend inopérantes, l’enjeu de notre propos est le suivant: caractériser la manière dont l’expérience sensible participe à la formation de collectifs . Les marcheurs solitaires, par leur désir de fuite (récréation sociale), recomposent dans l’environnement de la marche tout un tissu de relations aux êtres et aux choses qu’ils croisent et avec lesquels ils se sentent liés (re-création sociale). C’est à l’examen de ce lien, entre fantasme et réalité, que nous nous livrerons: au-delà de la récréation sociale ce serait bien la joie du corps, d’une part celle de se redécouvrir un corps plein de vitalité à partir duquel sentir pleinement le monde, et de l’autre celle de se vivre comme articulé à une multitude d’ autres , qui constituerait le fondement de l’expérience solitaire de la marche. Les marcheurs se vivent comme de simples composantes d’un ensemble plus vaste au sein duquel aucune discrimination véritable n’est établie entre humains et non-humains. Pour qu’il y ait société, il faut qu’il y ait du (des) corps, il faut également des passions, de l’affect. A tenir compte d’une assemblée élargie de tels corps (humains, vivants, matériels, naturels…), se forment sous les yeux du marcheurs et du sociologue, avec évidence, de nouveaux collectifs hybrides où le naturel et le culturel s’indéterminent l’un l’autre pour se fondre et se rendre tolérant l’un à l’autre.
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