SELFI: an object-based, Bayesian method for faint emission line source detection in MUSE deep field data cubes

International audienceWe present SELFI, the Source Emission Line FInder, a new Bayesian method optimized for detection of faint galaxies in Multi Unit Spectroscopic Explorer (MUSE) deep fields. MUSE is the new panoramic integral field spectrograph at the Very Large Telescope (VLT) that has unique capabilities for spectroscopic investigation of the deep sky. It has provided data cubes with 324 million voxels over a single 1 arcmin2 field of view. To address the challenge of faint-galaxy detection in these large data cubes, we developed a new method that processes 3D data either for modeling or for estimation and extraction of source configurations. This object-based approach yields a natural sparse representation of the sources in massive data fields, such as MUSE data cubes. In the Bayesian framework, the parameters that describe the observed sources are considered random variables. The Bayesian model leads to a general and robust algorithm where the parameters are estimated in a fully data-driven way. This detection algorithm was applied to the MUSE observation of Hubble Deep Field-South. With 27 h total integration time, these observations provide a catalog of 189 sources of various categories and with secured redshift. The algorithm retrieved 91% of the galaxies with only 9% false detection. This method also allowed the discovery of three new Lyα emitters and one [OII] emitter, all without any Hubble Space Telescope counterpart. We analyzed the reasons for failure for some targets, and found that the most important limitation of the method is when faint sources are located in the vicinity of bright spatially resolved galaxies that cannot be approximated by the Sérsic elliptical profile

The E-ELT first light spectrograph HARMONI: capabilities and modes

Trabajo presentado en SPIE Astronomical Telescopes, celebrado en San Diego (California), del 26 de junio al 1 de julio de 2016HARMONI is the E-ELT's first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the E-ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers (R 3500, 7500 and 20000) and instantaneous wavelength coverage spanning the 0.5 - 2.4 ¿m wavelength range of the instrument. In autumn 2015, the HARMONI project started the Preliminary Design Phase, following signature of the contract to design, build, test and commission the instrument, signed between the European Southern Observatory and the UK Science and Technology Facilities Council. Crucially, the contract also includes the preliminary design of the HARMONI Laser Tomographic Adaptive Optics system. The instrument's technical specifications were finalized in the period leading up to contract signature. In this paper, we report on the first activity carried out during preliminary design, defining the baseline architecture for the system, and the trade-off studies leading up to the choice of baseline

Modélisation tridimensionnelle de l'amorçage de l'arc électrique dans un disjoncteur basse-tension

Une méthode de résolution numérique de type éléments finis/volumes est adaptée à la modélisation d'un plasma d'arc. Le phénomène de rayonnement, les propriétés physiques du plasma et une équation d'état du plasma (tabulée) sont introduits dans le modèle.La résolution des équations de Maxwell par éléments finis est couplée à la résolution des équations de Navier-Stokes. L'introduction d'un maillage mobile permet de prendre en compte l'écartement des électrodes du disjoncteur. La modélisation met en avant plusieurs phases dans l'évolution de l'arc du disjoncteur : augmentation forte de sa température au début sous l'effet du chauffage brusque dû à l'initialisation, augmentation de la tension d'arc au cours du temps, expansion de l'arc entre les électrodes qui s'écartent et déplacement de l'arc en glissant vers le bout de l'électrode mobile, début de commutation de l'arc entre les deux rails fixes.This document describes direct numerical simulation of the first three milliseconds of a low-voltage circuit-breaker using computational-fluid-dynamics code adapted for electric-arc modelling. The mobile electrode is allowed for by a movint mesh. The results describe the evolution of the arc with time in terms of its detailed electrical, thermal and fluid dynamic properties. They allow the identification of several phases during the overall arc initiation process studied here : arc initialisation in the widening electrode gap, arc-thermal expansion, displacement of the arc towards the tip of the mobile electrode, and the beginning of commutation to the fixed electrodes.LYON-Ecole Centrale (690812301) / SudocSudocFranceF

ORIGIN: Blind detection of faint emission line galaxies in MUSE datacubes

Context. One of the major science cases of the Multi Unit Spectroscopic Explorer (MUSE) integral field spectrograph is the detection of Lyman-alpha emitters at high redshifts. The on-going and planned deep fields observations will allow for one large sample of these sources. An efficient tool to perform blind detection of faint emitters in MUSE datacubes is a prerequisite of such an endeavor. Aims. Several line detection algorithms exist but their performance during the deepest MUSE exposures is hard to quantify, in particular with respect to their actual false detection rate, or purity. The aim of this work is to design and validate an algorithm that efficiently detects faint spatial-spectral emission signatures, while allowing for a stable false detection rate over the data cube and providing in the same time an automated and reliable estimation of the purity. Methods. The algorithm implements (i) a nuisance removal part based on a continuum subtraction combining a discrete cosine transform and an iterative principal component analysis, (ii) a detection part based on the local maxima of generalized likelihood ratio test statistics obtained for a set of spatial-spectral profiles of emission line emitters and (iii) a purity estimation part, where the proportion of true emission lines is estimated from the data itself: the distribution of the local maxima in the “noise only” configuration is estimated from that of the local minima. Results. Results on simulated data cubes providing ground truth show that the method reaches its aims in terms of purity and completeness. When applied to the deep 30 h exposure MUSE datacube in the Hubble Ultra Deep Field, the algorithms allows for the confirmed detection of 133 intermediate redshifts galaxies and 248 Lyα emitters, including 86 sources with no Hubble Space Telescope counterpart. Conclusions. The algorithm fulfills its aims in terms of detection power and reliability. It is consequently implemented as a Python package whose code and documentation are available on GitHub and readthedocs

Three-dimensional modelling of electric-arc development in a low-voltage circuit-breaker

International audienc

Un mix électrique 100% renouvelable? Analyses et optimisations. Un travail d'exploration des limites du développement des énergies renouvelables dans le mix électrique métropolitain a un horizon 2050

In 2013, ADEME published its energy and climate scenarios for the period 2030 to 2050, suggesting possible avenues to achieve a four-fold reduction in greenhouse-gas emissions by 2050 by cutting energy consumption by half and deploying renewable energy sources for electricity generation on a substantial scale. Both of these objectives were the basis for targets set by the President of France and subsequently adopted by Parliament in the Energy Transition Law to promote green growth. With this new study, ADEME submits an exploratory scientific prospective study. Questions of balance between production and demand and cost efficiency of renewable-based electricity mixes are investigated through an advanced optimisation. The electricity mixes are theoretical: they are created from scratch and do not take into account the current situation or the path needed to achieve a 100% renewable-based electricity system. It aims at highlighting the technical measures to be implemented (strengthening grids, load shedding and storage) to support a policy of growth in renewable electricity technologies. It is also be used to identify the key factors for developing renewable technologies at lower cost such as lower costs of technologies, demand-side management, development of flexibility, support of R and D of least-mature technologies and the social acceptance of renewable electricity installations

The MUSE Hubble Ultra Deep Field Survey: I. Survey description, data reduction, and source detection

International audienceWe present the MUSE Hubble Ultra Deep Survey, a mosaic of nine MUSE fields covering 90% of the entire HUDF region with a 10-h deep exposure time, plus a deeper 31-h exposure in a single 1.15 arcmin2 field. The improved observing strategy and advanced data reduction results in datacubes with sub-arcsecond spatial resolution (0.̋65 at 7000 Å) and accurate astrometry (0.̋07 rms). We compare the broadband photometric properties of the datacubes to HST photometry, finding a good agreement in zeropoint up to mAB = 28 but with an increasing scatter for faint objects. We have investigated the noise properties and developed an empirical way to account for the impact of the correlation introduced by the 3D drizzle interpolation. The achieved 3σ emission line detection limit for a point source is 1.5 and 3.1 × 10-19 erg s-1 cm-2 for the single ultra-deep datacube and the mosaic, respectively. We extracted 6288 sources using an optimal extraction scheme that takes the published HST source locations as prior. In parallel, we performed a blind search of emission line galaxies using an original method based on advanced test statistics and filter matching. The blind search results in 1251 emission line galaxy candidates in the mosaic and 306 in the ultradeep datacube, including 72 sources without HST counterparts (mAB > 31). In addition 88 sources missed in the HST catalog but with clear HST counterparts were identified. This data set is the deepest spectroscopic survey ever performed. In just over 100 h of integration time, it provides nearly an order of magnitude more spectroscopic redshifts compared to the data that has been accumulated on the UDF over the past decade. The depth and high quality of these datacubes enables new and detailed studies of the physical properties of the galaxy population and their environments over a large redshift range

The E-ELT first light spectrograph HARMONI: capabilities and modes

HARMONI is the E-ELT’s first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the E-ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers (R ~3500, 7500 and 20000) and instantaneous wavelength coverage spanning the 0.5 – 2.4 μm wavelength range of the instrument. In autumn 2015, the HARMONI project started the Preliminary Design Phase, following signature of the contract to design, build, test and commission the instrument, signed between the European Southern Observatory and the UK Science and Technology Facilities Council. Crucially, the contract also includes the preliminary design of the HARMONI Laser Tomographic Adaptive Optics system. The instrument’s technical specifications were finalized in the period leading up to contract signature. In this paper, we report on the first activity carried out during preliminary design, defining the baseline architecture for the system, and the trade-off studies leading up to the choice of baseline

The ESO’s Extremely Large Telescope Working Groups

Since 2005 ESO has been working with its community and industry to develop an extremely large optical/infrared telescope. ESO’s Extremely Large Telescope, or ELT for short, is a revolutionary ground-based telescope that will have a 39-metre main mirror and will be the largest visible and infrared light telescope in the world. To address specific topics that are needed for the science operations and calibrations of the telescope, thirteen specific working groups were created to coordinate the effort between ESO, the instrument consortia, and the wider community. We describe here the goals of these working groups as well as their achievements so far