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Accueil > Le Laboratoire > Séminaires et conférences > Résumés 2017-2018

 Résumés 2017-2018

Remarque : les enregistrements des séminaires sont disponibles sur

6 July 2018 - 11h

  • Chiara Caprini (APC)
  • TBD


29 June 2018 - 11h

  • Joel Vernet (ESO)
  • TBD


22 June 2018 - 11h

  • Margaret Frerking (LESIA)
  • TBD


15 June 2018 - 11h

  • Elizabeth Stanway (Warwick)
  • TBD


8 June 2018 - 11h

  • Michael Gillon (Liège)
  • TBD


1 June 2018 - 11h

  • George Ellis
  • TBD


25 May 2018 - 11h

  • Jayne Birkby
  • TBD


18 May 2018 - 11h

  • Ravit Helled (Zurich)
  • TBD


20 April 2018 - 11h

  • Anne Verhamme (Obs. Genève)
  • Indirect probes of the escape of ionizing radiation from galaxies to unveil the nature of the sources of Cosmic Reionization

Cosmic reionization corresponds to the period in the history of the Universe during which the predominantly neutral intergalactic medium was ionised by the emergence of the first luminous sources. Young stars in primeval galaxies may be the sources of reionization, if the ionising radiation, called Lyman continuum (LyC), that they produce can escape their interstellar medium : the escape fraction of LyC photons from galaxies is one of the main unknowns of reionization studies. The increasing opacity of the intergalactic medium with redshift renders direct LyC detections impossible during reionisation. Indirect methods are the only probes of LyC leakage in the distant Universe. I will discuss three indirect diagnostics of LyC leakage that were recently reported in the literature. The first diagnostic for LyC leakage relates the escape of the strongly resonant Lyman-alpha radiation from galaxies to the LyC escape (Verhamme et al. 2015), and was recently validated by observations (Verhamme et al. 2017). The second diagnostic proposes that the strength of Oxygen lines ratios can trace density-bounded interstellar regions. It was the selection criterion for the successful detection of 6 strong Lyman Continuum Emitters from our team (Izotov 2016a,b, 2018). The third diagnostic relates the metallic absorption line strengths to the porosity of the absorbing interstellar gas in front of the stars. These diagnostics will soon become observables at the redshifts of interest with JWST.

13 April 2018 - 11h

  • Gabriel Pratt (CEA Saclay)
  • The Advanced Telescope for High-Energy Astrophysics

The Advanced Telescope for High-Energy Astrophysics (ATHENA) is ESA’s second Large mission, expected to launch in 2030. An observatory mission combining a telescope with large collecting area and state of the art imaging and high resolution spectroscopic capabilities, Athena is expected to give rise to a transformational leap in our understanding of hot cosmic plasmas. I will describe the current mission design and give an overview of some of the scientific goals, with an emphasis on large scale structure science.

6 April 2018 - 11h

  • Eiichiro Komatsu (MPA)
  • Finding Cosmic Inflation

The cosmic microwave background (CMB) research told us a remarkable story : the structure we see in our Universe such as galaxies, stars, planets, and eventually ourselves originated from tiny quantum fluctuations generated in the early Universe. With the WMAP we have confirmed many of the key predictions of inflation including flatness and statistical homogeneity of our Universe, Gaussianity and adiabaticity of primordial density fluctuations, and a small but non-zero deviation from the scale-invariant spectrum of density fluctuations. Yet, the extraordinary claim requires extraordinary evidence. The last prediction of inflation that is yet to be confirmed is the existence of primordial gravitational waves whose wavelength can be as big as billions of light years. To this end we have proposed to JAXA a new satellite mission called "LiteBIRD",
whose primary scientific goal is to find signatures of gravitational waves in the polarisation of the CMB. In this presentation we describe the current state of affairs regarding our understanding of the early Universe, physics of polarisation of CMB, and the LiteBIRD proposal.

30 March 2018 - 11h

  • Pratika Dayal
  • The first billion years of galaxy formation

Galaxy formation in the first billion years mark a time of great upheaval in the history of the Universe : as the first sources of light, these galaxies ended the ’cosmic dark ages’ and produced the first photons that could break apart the hydrogen atoms suffusing all of space starting the process of cosmic reionization. As the earliest building blocks, the shapeless ellipticals galaxies that formed in the first billion years also determine the physical properties of all subsequent galaxy populations. At the forefront of astronomical research, the past few years have seen cutting-edge instruments provide tantalising glimpses of such galaxies chaotically assembling in an infant Universe. I will show how this data has provided an unprecedented opportunity to pin down the reionization state of the Universe (at least in its last stages), understand their physical properties, and study the key physics driving their formation and evolution. Finally, I will try to give a flavour of how the assembly of early galaxies, accessible with the forthcoming James Webb Space Telescope and the associated reionization history, can provide a powerful testbed for Warm Dark Matter models.

23 March 2018 - 11h

  • Olivier Witasse (ESTEC)
  • JUICE : A European Mission to Jupiter and its Icy Moons

JUICE - JUpiter ICy moons Explorer - is the first large mission in the ESA Cosmic Vision programme. JUICE is due to launch in May 2022. It will arrive at Jupiter in October 2029, and will spend three years characterizing the Jovian system, the planet itself, its giant magnetosphere, and the giant icy moons Ganymede, Callisto and Europa. The spacecraft will then orbit Ganymede for a few months. One of the main goals of JUICE is to explore the habitable zone around Jupiter. Ganymede is a high-priority target because it provides a unique laboratory for analyzing the nature, evolution and habitability of icy worlds, including the characteristics of subsurface oceans. The payload consists of 10 instruments plus a ground-based experiment using the VLBI network. The speaker is the JUICE project scientist and he will explain the mission, the science, the challenges (technical, human), with the help of short videos and animations.

16 March 2018 - 11h

  • Frans Snik (Leiden)

To directly image and characterize exoplanets, we need advanced optical
systems on current Very Large and future Extremely Large telescopes that
can suppress the bright glare of stars by 6-10 orders of magnitude, and
analyze the feeble light of potential planetary companions. Such
high-contrast imaging systems consist of advanced adaptive optics and
associated wavefront sensing techniques, coronagraphy to (locally)
suppress the diffracted starlight, contrast-enhancing techniques like
angular/spectral/polarimetric differential imaging, and diagnostic
capabilities like (high-resolution) spectroscopy and
(spectro)polarimetry. In our group in Leiden we cover all these
different aspects of high-contrast imaging, with the aim to achieve the
ultimate contrast performance and characterization potential with a
complete, integrated end-to-end system for ground-based telescopes. We
are currently exploiting brand-new liquid-crystal technologies that
offer important performance benefits for many components in a
high-contrast imaging instrument, and for the system as a whole. We have
introduced the “vector-APP” coronagraph that has currently been
successfully commissioned at MagAO, LBT, and SCExAO, and are developing
versions for several other telescopes and instruments, including a
stratospheric balloon telescope. We apply lessons learnt from the
vector-APP to the Vector Vortex Coronagraph to enhance its spectral
range and suppression. Novel versions of the vector-APP now have several
methods for focal-plane wavefront sensing built in, and we are currently
also testing versions of Pyramid and Zernike wavefront sensors with
enhanced performance thanks to liquid-crystal implementations. As
vector-APP coronagraphs are broadband, we are applying them for
integral-field spectroscopy, and developing versions that are optimally
matched to fiber-fed spectrographs. And as the vector-APP is based on
polarization tricks, we are extending it with polarimetric
implementations. We are currently even playing with crazy
liquid-crystal-based Sparse Aperture Masking concepts that are heavily
multiplexed, and can include achromatic nulling. I will provide an
overview of these projects, and an outlook for implementing such
techniques at the VLT and the ELT to ultimately characterize rocky
planets in the habitable zones of nearby stars.

23 February 2018 - 11h

  • Fabrice Madec (LAM)
  • Zoom sur les intégrations et les tests du spectrographe de l’instrument PFS

L’instrument Prime Focus Spectrograph (PFS) du projet Subaru Measurement of Images and Redshifts (SuMIRe) est développé par un large consortium international pour le télescope japonais SUBARU à Hawaii. Ce spectrographe multi-objet de 2400 fibres est dédié à la cosmologie, l’étude de l’énergie et de la matière noire ainsi qu’à l’évolution des galaxies et l’archéologie galactique. Nous commencerons par une présentation générale de l’instrument, les spécificités du projet, les interfaces. Ensuite, nous entrerons plus dans le détail des activités d’intégration et de test du spectrographe qui sont faites au LAM. Enfin, nous finirons par une présentation des futures étapes de l’instrument.

16 February 2018 - 11h

  • Philippe Andre (Laboratoire d’Astrophysique AIM Paris-Saclay)
  • From Filamentary Networks to Protostellar Cores in Giant Molecular Clouds : Toward a Unified Picture for Star Formation in Galaxies

I will review recent progress in our observational understanding of the
link between the structure of molecular clouds and the formation of low-
to intermediate-mass stars. In particular, I will describe the low-mass star formation scenario favored by Herschel studies of the nearest molecular clouds of the Galaxy which point to the key role of the quasi-universal filamentary structure pervading the cold ISM. The Herschel results support a picture in which molecular filaments and prestellar cores represent two fundamental steps in the star formation process : First, large-scale compression of interstellar material in supersonic MHD flows generates a cobweb of 0.1 pc-wide filaments in the ISM ; second, the densest filaments fragment into prestellar cores (and subsequently protostars) by gravitational instability, while simultaneously growing in mass and complexity through accretion of background cloud material. This filamentary paradigm provides new insight into the origin of the stellar initial mass function and the efficiency of star formation in the dense molecular gas of galaxies. I will end with several open issues and future directions.

9 February 2018 - 11h

  • Frederique Motte (Université Grenoble Alpes)
  • High-mass star and cluster formation in the Milky Way : the Herschel/HOBYS, IRAM/W43-HERO and ALMA-IMF view

The physical process by which stars inherit their properties, especially their mass, from those of their parental cloud is the fundamental issue that guides all star formation studies. Our knowledge of this legacy has profound implications for many areas of astrophysics, including the cosmic history of star formation in galaxies. The star-formation recipes commonly used, among which the origin of the initial mass function (IMF) and star formation rates (SFR), are considered to be universal and thus independent of galactic environments. Our recent studies challenge these recipes, which are related to our understanding of star formation.

I will present the Herschel discovery of high-density cloud filaments, which are forming clusters of OB-type stars. Given their high star formation activity, these so-called mini-starburst clouds/ridges could be seen as “miniature and instant models” of starburst galaxies. The characteristics of mini-starburst ridges investigated with the NOEMA and ALMA interferometer challenge star formation models and shed light on the origin of massive clusters. In one of these ridges, the measured star formation rates (SFR) contradicts statistical models of star formation rates. Moreover, its measured core mass distribution suggests that the stellar initial mass function (IMF) may not be determined, in these extreme environments, at the prestellar stage.
These results motivated the setting up the ALMA-IMF Large Program, project, which was accepted for Cycle 5 and whose source sample and main objectives will be presented.

2 February 2018 - 11h

  • Michèle Péron (ESO)
  • Diversité et inclusion en ingénierie et astronomie
    (Grand Public)

Une main-d’¦uvre diversifiée est essentielle à la satisfaction au
travail, à l¹innovation et à la capacité d’une organisation d’attirer et
de retenir les talents. Pour assurer un environment diversifié et créatif,
il est important d¹éliminer non seulement les barrières systémiques
(manque de femmes qui s¹engagent dans des études scientifiques) mais
également les barrières comportementales comme par example les préjugés
inconscients. Cette présentation donnera un aperçu des résultats de la
recherche sur l¹impact de ses préjugés inconscients dans le monde du
travail. Elle mettra également en lumière diverses initiatives qui
existent pour améliorer la diversité et l’inclusion en ingénierie.

26 January 2018 - 11h

  • Louis le Sergeant d’Hendecourt (PIIM)
  • From Astrochemistry to Astrobiology : the role of extraterrestrial ices in the build-up of a prebiotic chemistry on telluric planets

Extraterrestrial ices are observed in many astrophysical environments linked to the formation of stars and planetary systems but also disks and various debris such as comets and asteroids. The chemical evolution of these ices following photo- and thermo-chemistry is routinely simulated in the laboratory. These simulations always end up with the building up of organic materials (semi refractory residues) that show the presence of many molecular bricks of life such as amino acids, nucleobases and sugars, including ribose, a key constituent of RNA. These organics do show also similarities with carbonaceous chondrites and thus suggest an astrophysical scenario in which the delivery of these materials on the primitive Earth may be important, if not essential to prebiotic chemistry. A general view of these processes will be discussed.

19 January 2018 - 11h

  • Don Pollacco (Warwick)
  • Transit surveys of the past, present and future : the search for Earth 2

Twenty years ago the first exoplanet transit was detected. Whilst rare events, transits are important as they give (accurate) information that cannot be obtained by any other means. In this talk I will review the status of transit surveys by looking at the original ground based surveys and how they have evolved to become state of the art with data approaching that of the quality of space based surveys. In addition I will examine the fundamental discoveries that have come from Space surveys and look forward to exciting results expected over the next decade.

12 January 2018 - 11h (Cancelled)

  • Bernard Marty (CRPG Nancy)
  • Contribution of volatile elements to Earth based on the analysis of Comet 67P/C-G

Comets are among the most pristine solar system materials. Their abundant volatile species, mainly in the form of ices, are intimately mixed with refractory silicate-rich phases and organics, the origins of which - either in the protosolar disk or the molecular cloud/interstellar medium - are actively debated.
The origin of cometary matter and the potential contribution of comets to inner planet atmospheres are long-standing problems that were central in the definition of the ESA Rosetta mission exploring Comet 67P/Churyumov-Gerasimenko (67P/C-G). Noble gases are key tracers for the origin(s) and processing of volatile elements in the nascent solar system and in planetary atmospheres. The analysis of argon in Comet 67P/C-G has shown that comets are rich in noble gases, suggesting that a significant fraction of these elements in the terrestrial atmosphere could be cometary.
The Double Focusing Mass Spectrometer ROSINA DFMS has detected during a dedicated period in May 2016 not only argon, but also krypton and xenon. In this talk we will present the results with special emphasis on Xe, and discuss the implications for solar system formation scenarios, as well as for the origin of volatile species on inner planets.

19 December 2017 - 14h

  • Firas Mazyed (LAM)
  • Studying and Analysing Multi-wavelength Observations of Galaxies Observed by Herschel (Thesis defence)

15 December 2017 - 11h

  • Daisuke Kawata (UCL)
  • Thick and thin disk formation and evolution in the Milky Way

Spectroscopic studies of the abundances of the Galactic disk stars clearly revealed two metal abundance sequences, at high-[alpha/Fe] and low-[alpha/Fe], and high-[alpha/Fe] stars are generally older than low-[alpha/Fe] stars. These old high-[alpha/Fe] and young low-[alpha/Fe] populations are often considered as the thick and thin disk components, respectively. Based on the results of the Auriga cosmological simulations, we demonstrate that two pathways of the disk formation scenarios can naturally explain the observed distribution of these chemically distinct thick and thin disk stars in the Milky Way. We then discuss that the thin disk formation drives the radial migration of stars due to the development of the bar and the spiral arms, and the vertical metallicity gradients for the mono-age populations, which we observed in the Gaia DR1+RAVE data, provide strong constraints on the radial migration and the structure of the Galactic thin disk.

8 December 2017 - 11h (Cancelled)

  • No seminar

5 December 2017 - 14h

  • Wilfried Jahn (LAM)
  • Innovative focal plane design for high resolution planetary observation - Freeform optics and curved sensors (Thesis defence)

1 December 2017 - 11h

  • Joop Schaye (Leiden)
  • Simulating the formation of galaxies

The realism of hydrodynamical simulations of the formation and evolution of populations of galaxies has improved considerably in recent years. I will try to give some insight into the reasons behind this success, focusing in particular on the importance of subgrid models and the associated limitations. I will also present recent results from the cosmological EAGLE simulations as well as from other projects.

30 November 2017 - 15h

  • Sara Pipien (LAM)
  • A la recherche de quasars à grand décalage spectral dans le sondage CFHQSIR (Thesis defence)

27 November 2017 - 14h30

  • Romain Alata (LAM)
  • Instrumentation pour l’astronomie et métrologie à l’aide de MOEMS (Thesis defence)

24 November 2017 - 11h

  • Olivier Absil (Liege)
  • Five years of harvest with the vortex coronagraph

While the concept of vortex coronagraphy dates back to 2005, the first science-grade Annular Groove Phase Masks (AGPM), working in the thermal infrared regime, have been installed at the VLT only in 2012. They are now also equipping the Keck telescope and the Large Binocular Telescope, and will soon be at the core of more ground-based high-contrast imaging instruments. In this seminar, I will shortly review the technology development undertaken over the last 12 years, and describe the on-sky operations and performance of the vortex coronagraph. I will then present the main scientific results obtained since 2012, and explain how we have recently adapted deep learning techniques to the problem of post-processing in high-contrast imaging. I will finally discuss the perspectives with new instruments, including the Breakthrough Watch project.

17 November 2017 - 11h

  • Mathieu Puech (GEPI)
  • Rotating discs vs. mergers at z 1 : is there really a disc survival issue in LCDM ?

Discs represent 70% of local massive spirals. Such a large fraction has been suggested to be in tension with the relatively high occurrence rate of major mergers at higher redshifts in LCDM, which has been dubbed as the "disc survival issue". Observations of the spatially-resolved kinematics and the high resolution morphology of their progenitors at z=0.6-1.2 suggest that gas-rich mergers is a viable solution to this issue. I will review observational evidences for this with a particular focus on the counter-arguments that have been discussed in the community, e.g., the existence of a main sequence of star forming galaxies, the large fraction of (U)LIRGs with spiral morphologies, the low fraction of the SFR attributed to major mergers, or the large fraction of spiral galaxies with no classical bulges (ie, pseudo-bulges and bulgeless). I will show that none of these arguments are actually valuable counter-proofs of the prominent role of gas-rich major mergers in shaping a large fraction of local spiral galaxies. Finally, I will discuss the current and future reliability of rotation curve measurements in distant galaxies, focusing in particular on MOSAIC, the future ELT multi-object spectrograph.

10 November 2017 - 11h

  • Jens Chluba (Manchester)
  • Cosmology Beyond Thermal Equilibrium : Future Steps with CMB spectral distortions

Since the measurements with COBE/FIRAS in the mid-90’s we know that the energy spectrum of the cosmic microwave background (CMB) is extremely close to that of a perfect blackbody. However, a number of early Universe processes should create spectral distortions at a level within reach of present day technology. I will give a broad-brush overview of recent theoretical and experimental developments, explaining why future measurements of the CMB spectrum will open an unexplored new window to early-universe and particle physics. This provides an exciting new path forward in CMB cosmology which is complementary to planned and ongoing searches for primordial B-mode polarization signals. I will also highlight some of the challenges due to foregrounds.

27 October 2017 - 14h

  • Anaïs Bernard (LAM)
  • Développement de nouveaux outils de traitement et d’analyse pour l’Optique Adaptative Grand Champ (Thesis defence)

20 October 2017 - 11h (Cancelled)

  • Louis le Sergeant d’Hendecourt (PIIM)

13 October 2017 - 11h

  • Carlos Frenk (Durham)
  • A conclusive test of Cold Dark Matter

The "Lambda cold dark matter’’ (LCDM) cosmological model is one of the great achievements in Physics of the past thirty years. Theoretical predictions formulated in the 1980s turned out to agree remarkably well with measurements, performed decades later, of the galaxy distribution and the temperature structure of the microwave background radiation. Yet, these successes do not inform us directly about the nature of the dark matter. Indeed, there are competing (and controversial) claims that the dark matter might have already been discovered, either through the annihilation of cold, or the decay of warm, dark matter particles. In astrophysics the identity of the dark matter manifests itself clearly in the properties of dwarf galaxies, such as the satellites of the Milky Way. I will discuss predictions from cosmological simulations assuming cold and warm (in the form of sterile neutrinos) dark matter and show how astronomical observations can conclusively distinguish between the two.

6 October 2017 - 11h

  • Paolo Padoan (Barcelona)
  • Supersonic Turbulence and Star Formation

Supersonic turbulence and star formation are intimately linked. On the one hand, the ubiquity of supersonic turbulence in the cold interstellar medium can be explained as the consequence of star formation, because massive stars explode as supernovae, releasing enough energy to sustain the turbulence. On the other hand, star formation can be viewed as the consequence of supersonic turbulence, because protostellar cores originate from random density enhancements caused by shocks in the turbulent flow. This direct link between turbulence and star formation is the fundamental reason why the star formation process may self-regulate at large scales ; it is also the fundamental reason for the apparent universality of the star formation rate and of the stellar mass distribution. Having unveiled the statistical properties of supersonic turbulence, primarily through numerical studies, we are now able to derive a statical theory of star formation where both the star formation rate and the initial mass function of stars can be predicted as a function of the fundamental non-dimensional parameters of star-forming regions, such the ratios between kinetic, gravitational, magnetic and thermal energies.

2 October 2017 - 10h30

  • Sara Jamal (LAM)
  • Spectral analysis of the Euclid survey data (Thesis defence)

26 September 2017 - 14h

  • Anna Niemiec (LAM)
  • Influence of the environment on galaxy evolution (Thesis defence)

25 September 2017 - 14h

  • Ana Acebron (LAM)
  • Cosmography with strong lensing in galaxy clusters (Thesis defence)

20 September 2017 - 14h

  • Miguel Figueira (LAM)
  • Ionized regions and star formation in the Galaxy (Thesis defence)

15 September 2017 - 11h

  • Eric Prieto (LAM)
  • Tests d’intégration de NISP au LAM (Grand public)

1. Présentation générale du NISP (Performance)
2. Présentation de la structure (par T. Pamplona)
3. Présentation du plan focal (par A. Bonnefoi)
4. Présentation du grism (par A. Costille)
5. Présentation des AIV/T

11 September 2017 - 14h

  • Olivier Fauvarque (LAM)
  • Optimization of Fourier based wave front sensors (Thesis defence)

8 September 2017 - 11h

  • Roland Bacon (Lyon)
  • The MUSE Hubble Deep Field Survey

The MUSE Hubble Deep Field Survey is deepest spectroscopic survey ever performed over the entire Ultra Deep Field (UDF) area. It provides 1700 spectroscopic redshifts, an order of magnitude more compared to the data that has been accumulated on the UDF over the past decade, up to AB 30 in magnitude and 6.7 in redshift. The depth and high quality of the data enables new and detailed studies of the physical properties of the galaxy population and their environments over a large redshift range. In this talk I will show in advance of publication a number of important results achieved by the survey on a diversity of topics : investigation of bias in photometric redshift, spatially resolved stellar kinematics at z 1, properties of CIII emitters, FeII emission in stellar forming galaxies, Lya luminosity function and its impact for reiniozation, Lya extreme EW objects undetected in UDF, Lya extended halos, evolution of the galaxy major merger rate with redshift, etc.

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