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Accueil > Le Laboratoire > Séminaires et conférences > Past Seminars > Résumés 2014-2015

 Résumés 2014-2015

26 June 2015 - 11h

  • Yannick Mellier (IAP)
  • Euclid space mission in search of dark energy

The discovery of the accelerating expansion of the Universe leads cosmologists to postulate the existence of dark energy that would be the dominant component of matter-energy content of the current Universe. Thus, 95% of the universe would consist of dark matter and dark energy whose nature we are totally unknown. They present challenges for physicists exciting, which could see the birth of a new physical around these two fundamental components. The space mission ESA Euclid was selected by the European Space Agency to provide answers concerning the true nature of the Universe Black and reveal new physics underlying. During this conference, I will present the scientific and technical issues this mission particularly complex high precision, and it should teach us about dark matter, dark energy, the history of the Universe and its future.

19 June 2015 - 11h

  • Brice-Olivier Demory (Cambridge, UK)
  • Exoplanet Characterisation from Space : from Gas Giants to Super Earths

In the past ten years, space-based facilities have propelled exoplanet science to a level far beyond our hopes. I will review recent results that have contributed to improve our knowledge of hot-Jupiter and super-Earth properties. I will discuss how the combination of datasets from instruments operating at different wavelengths allow us to better understand the climate patterns in highly irradiated gas giant atmospheres. I will also describe current progress toward the characterisation of super-Earths, which are planets with masses and radii between those of Neptune and the Earth. I will present the results of a new program employing both Kepler and Spitzer space telescopes to better understand super-Earths properties, by combining observations obtained in different wavelength regimes. Notably, we find that some super-Earths initially thought to be volatile-rich exhibit circulation patterns matching a rocky composition, requiring new developments regarding our knowledge of super-Earth interiors. I will finally briefly describe the prospects towards the detection of life beyond Earth within the next decade.

5 June 2015 - 11h

  • Gabriella de Lucia (INAF)
  • Theoretical models of galaxy formation and evolution. Latest developments and future directions

I will review the current status of hierarchical models of galaxy formation and evolution, emphasizing a number of problems that appear to be common to all recently published models. I will then describe a new method to account for the finite lifetimes of stars and trace individual abundances within a semi-analytic model of galaxy formation. At variance with previous methods, based on the storage of the (binned) past star formation history of model galaxies, the new method projects the information about the metals produced by each simple stellar population (SSP) in the future. Using this approach, an accurate accounting of the timings and properties of the individual SSPs composing model galaxies is possible. I will present results obtained by applying the model to six simulated haloes of roughly Milky Way mass and with no massive close neighbour at z=0. Finally, I will describe recent work based on the same model applied to larger cosmological scales, and will describe future prospects.

29 May 2015 - 11h

  • Guinevere Kauffmann (MPIA)
  • Atomic and Molecular Gas Properties of Galaxies : constraints on galaxy formation models

Galaxies form when gas is able to cool, condense and form stars within dark matter halos. Over the past 5 years, there have been a number of efforts aimed at linking the atomic and molecular gas properties of nearby galaxies to their stellar properties in a systematic way. This talk will describe the main results obtained by recent surveys carried out using the Arecibo, IRAM and Westerbork radio telescopes, and what we have learned about the late stages of galaxy formation.

19 May 2015 - 11h

  • Tim de Zeeuw (ESO)
  • Building the world’s largest telescopes at ESO

ESO is an intergovernmental organisation for astronomy founded in 1962 by five countries. It currently has 14 Member States in Europe with Poland and Brazil poised to join as soon as the respective Accession Agreements have been ratified. Together these countries represent approximately 30 percent of the world’s astronomers. ESO operates optical/infrared observatories on La Silla and Paranal in Chile, partners in the sub-millimetre radio observatories APEX and ALMA on Chajnantor and has started construction of the Extremely Large Telescope on Armazones near Paranal. The colloquium will provide an overview of the entire programme, with emphasis on recent developments, and will briefly touch on opportunities for the future.

24 Apr 2015 - 11h

  • David Mouillet (IPAG)
  • The SPHERE instrument for imaging exoplanetary systems

Direct imaging of planetary systems around other stars, many and varied, has an important and complementary role of other detection techniques. The difficulty of this observational challenge requires the implementation of new technology, a complete rethinking and specifically to optimize the imaging performance with very high contrast. Actually dedicated to the great contrast instruments have been proposed for the first time there is a dozen years. The instrument SPHERE is the result of such an ambitious project, combining the expertise of ten European institutes, including the LAM was essential. This instrument is now installed on a telescope of 8-m in Chile and is available to the international community.
After highlighting some central elements of design choices and implementation of this instrument, both from the technological point of view, system and scientific analysis, and operation, we will see how these characteristics differentiate an instrument conventional imaging. These new capabilities represent a success compared to the initial objectives and the broader context of the study of exoplanetary systems, with a particular interest in the early phases of these systems during and shortly after their formation.
This adventure also now allows a return on experience in the analysis of the expected limitations, technological obstacles, new instrument concepts needs and also the project organization, informative experience from the perspective of the new challenges in the future to imaging and ever more precise characterization of exoplanets, until exoplanetology compared to our own solar system.

17 Apr 2015 - 11h

  • Seb Oliver (Sussex UK)
  • The history of star formation, obscured by dust and revealed by Herschel

One of the primary motivations for Herschel was to explore star formation in the distant Universe. To address this topic Herschel invested significant fraction of its time in undertaking survey including the multi-tiered extragalactic survey, HerMES. HerMES mapped around 400 sq. degrees in the best studied extragalactic fields on the sky and has uncovered 100s of thousands of distant star forming galaxies. In this talk I will review some of the key results from HerMES. In particular the Herschel maps reveal most of the cosmic infrared background and these and other basic statistical measurements have constrained our view on galaxy evolution models. I will summarise what we have learned about the cosmic history of star formation. I will show how clustering measurements have been used to reason that these distant star forming galaxies are the progenitors of present day, massive galaxy, decedents. I will show how Herschel has revealed new insights into the relation between star formation and central supermassive black hole accretion activity. Finally I’ll illustrate how Herschel is uncovering starburst galaxies when the Universe was less than a billion years old.

10 Apr 2015 - 11h

  • Katarina Kovač (ETH Zurich)
  • Quenching of star formation in different environments over 0<z<0.7 : centrals, satellites, and galactic conformity

I will discuss the role of environment in quenching of galaxies over 0 < z < 0.7 using the SDSS and the final zCOSMOS-bright data sets. Generally, the quenched fraction of galaxies increases with the environmental overdensity and with the stellar mass, consistent with previous works. Up to z=0.7, the quenched fraction appears to be separable in mass and environment, suggesting the action of two processes : mass and environmental quenching. While the quenched fraction of centrals is consistent with being produced through the mass-quenching channel only, the observed fraction of quenched satellites requires an additional mechanism - i.e. environment quenching to play a role. The excess in the quenched fraction of satellites with respect to the centrals is sufficient to explain the majority of the environmental quenching in the overall population of galaxies. In addition, we find that the quenched fraction of satellites also depends on the properties of central galaxies residing in the same halo : a larger fraction of the satellites of the quenched centrals are quenched than those of star-forming centrals (i.e. galaxy conformity), indicating the existence of some common hidden variable related to the quenching in the whole group and not only to the quenching of satellites. We can explain this effect within our modified HOD framework which correlates galaxy colours with the concentration of the parent halo, making the older, more concentrated haloes at fixed mass preferentially host quenched galaxies.

3 Apr 2015 - 11h

  • Jean-Pierre Luminet (LAM)
  • L’invention du BIG-BANG (Un livre Un auteur)

Tout le personnel LAM, PYTHEAS, POP-SUD, (y compris doctorants, post-docs, stagiaires, CDD,..) est invité à cette conférence tout public (affiche en pièce jointe), qui sera suivie d’une collation dans le hall d’accueil.

27 Mar 2015 - 11h

  • Elena Masciadri (INAF)
  • Gender equality in science and astronomy : state of art

The ’gender equality’ issue is a general and important feature of our professional life. It indicates the necessity to assure parity in work opportunities, intellectual recognition, access to professional benefits, presence in decisions making bodies and scientific advisory committees. It is commonly perceived as a ’female problem’ and, even if in the most recent years the situation is less critical than several decades ago, it is still an unsolved problem.
In this seminar I will try to trace the state of art in the research field and in particular in the scientific field and in the sub-sample of astronomy providing information and answers to a few among the most common questions related to this topic : are women employed as researchers still a minority ? Are women effectively progressing in their career to achieve top levels positions ? Does the gender gap penalize only women or also men ? Can the under-representation of women be justified by a weaker skill quality of women ? Which are the main causes of discrimination and which are the possible solutions ? Is the gender equality issue something we have to take care ?

20 Mar 2015 - 11h (cancelled)

  • Richard Davies (MPE)

13 Mar 2015 - 11h (cancelled)

  • Thierry Contini (IRAP)

13 Feb 2015 - 11h

  • Jorge Penarrubia (Edinburgh)
  • Testing Dark Matter particle models with dwarf spheroidals

Dwarf spheroidal galaxies are the faintest galaxies in the Universe and as such play a fundamental role in galaxy formation models. In addition, their internal kinematics suggest the presence of large amounts of non-baryonic matter, making these objects excellent laboratories to test cosmological predictions on the smallest scales. In models where dark matter consists of exotic particles formed shortly after the Big Bang, the high phase-space densities inferred in dwarf spheroidals can put strong bounds on the microscopic properties of several particle candidates. However, a definite test of dark matter models requires a better understanding of the impact of baryonic feedback on the current dark matter distribution. Remarkably, to date none of the existing cosmological models appear to successfully reproduce the observed properties of the bright Milky Way dwarfs. This talk will give an overview of the existing conflicts between theory and observations within the current paradigm, as well as of some alternative scenarios that have been proposed to explain the extreme properties of dwarf spheroidal galaxies.

6 Feb 2015 - 11h

  • Frantz Martinache (OCA)
  • Single-telescope interferometry

In 1873, Stephan performed, at Observatoire de Marseille, the first interferometric observations of stars, looking at fringes produced by a 2-hole mask placed in front of the 80-cm aperture of Foucault’s telescope. Fast forward to 2015 : the current generation of 8 to 10-meter class telescopes are all equiped with adaptive optics (AO) that produces ideal diffraction limited images. Yet somehow, most of these same telescopes still do implement some form or another of Stephan’s original masking experiment. How can this 19th century technology still be so relevant today ? I will show you how the self-calibration interferometric technique known as closure-phase it enables, is used to recover faint companions, sometimes even beating the conventionally accepted diffraction limit. I will also show you how recent research shows that the concept of closure-phase can be expanded upon, and how surprisingly, one is able to take advantage of the same self-calibration tricks, without using a mask at all. From HST NICMOS to ground based AO data, looking at diffraction limited images with this new framework opens the way to super-resolution imaging.

30 Jan 2015 - 11h

  • Cecilia Ceccarelli (Grenoble)
  • How to catch cosmic rays and energetic protostellar winds sources by observing molecules

At large scales, Cosmic Rays (CR) permeate our Galaxy and ionise the UV-shielded molecular gas, which makes them crucial actors in shaping the InterStellar Medium (ISM) and governing star and planet formation. At smaller scales, newly born stars are suspected to be sources of energetic protostellar winds, which likely affect the planet formation process. In the Solar System, traces of some short-lived radionucleides (e.g. 10Be) in meteoritic material suggest that the young Sun emitted an important flux of >MeV particles. These two cases, CR and energetic protostellar winds, have in common the fact that >MeV particles are impossible to directly detect, as they are scattered by the galactic magnetic fields. In this presentation, I will show that relatively cold (<100K) molecules can be used to catch the sources emitting MeV-GeV particles and, consequently, study them. Specifically, I will present observations that allowed us to infer the presence of an enhanced flux of CR and their MeV-GeV versus TeV spectrum towards molecular clouds close to some SuperNova Remnant (SNR). Using a similar technique, we revealed large fluxes of >MeV particles, similar to that necessary to explain the meteoritic 10Be presence, in a protocluster system that will eventually form a Solar-like planetary system. Finally, I will conclude with some prospectives opened up by similar studies in different sources, for example the environments close to Active Galactic Nuclei (AGNs).

23 Jan 2015 - 11h

  • Matthew Pieri (LAM)
  • In the Deep, Dark Lyman-alpha Forest : Exploring Dark Energy and Galaxy Formation using the Intergalactic Medium

I will discuss probes of the intergalactic medium measuring both the largest and smallest scale effects in the extragalactic universe. The Lyman-alpha forest along the line-of-sight to background quasars is measured providing a new kind of survey. The BOSS survey (as part of SDSS-III) has probed more than 60,000 Gigaparsecs in path length and is still growing. We have made the first measurements of baryon acoustic oscillations on 150 Megaparsec scales to probe the expansion of the universe, and have seen evidence of clumping in regions around galaxies on 30 parsec scales. I will discuss the future of such surveys and the key role France plays both now and into the future.

16 Jan 2015 - 11h

  • François Bouchet (Paris)
  • Derniers résultats cosmologiques de Planck / Latest cosmological results from Planck

Sketched out in 1992, selected by ESA in 1996, launched in 2009, Planck delivered a first set of results in March 21st 2013, in particular the map of the anisotropies of the Cosmic Microwave Background (CMB). The later displays minuscule variations as a function of the observing direction of the temperature of the fossil radiation around its mean temperature of 2.725K. I will described the new results we just obtained from the analysis of all the data acquired during the mission (more than twice as much as before), including for the first time the polarisation measurements. CMB anisotropies reveal the imprint of the primordial fluctuations which initiate the growth of the large scale structures of the Universe, as transformed by their evolution, in particular during the first 370 000 years. Both temperature and polarisation anisotropies teach us, independently or jointly, the possible value of the parameters of the models when confronted to data. I will review the new Planck cosmology, both in terms of content of the universe and of characteristics of the primordial fluctuations.

9 Jan 2015 - 11h

  • Anne Dutrey (Bordeaux)
  • Observations of protoplanetary disks with PdBI and ALMA

Protoplanetary disks orbiting around TTauri stars are seen as nurseries of planetary systems. In the last ten years, molecular and continuum images of these disks provided by mm/submm interferometers have begun to unveil their complex
physics and chemistry. Using recent observations from the IRAM array and ALMA, I will discuss their physical properties and show that, thanks to ALMA, our view of these objects is rapidly evolving.

5 Dec 2014 - 11h

  • Marc Ferrari, Johan Floriot and Emmanuel Hugo (LAM)
  • POLARIS (grand public)

Le vendredi 5 decembre à 11h aura lieu au LAM un séminaire grand public sur POLARIS par Marc Ferrari, Johan Floriot et Emmanuel Hugo. Le séminaire, destiné à une large audience, sera en français et tout le personnel est cordialement invité à venir y participer.
Ce séminaire grand public, ouvert à tout le personnel du site, présentera la plateforme de polissage POLARIS, l’historique scientifique et technique de sa mise en place ainsi que les projets scientifiques en cours ou à venir sur celle-ci.
Cette plateforme, unique en Europe, permet de réaliser des optiques asphériques d’excellente qualité jusqu’à des diamètres de 2.5m. Elle s’appuie sur l’expertise phare du laboratoire en matière de fabrication optique, notamment sur la technique dite de polissage sous-contrainte, véritable savoir-faire du laboratoire.
Cette technologie, qui a d’ailleurs donné lieu à un brevet, est aujourd’hui en cours d’évaluation à l’échelle 1 sur la plateforme POLARIS, dans le cadre d’un contrat de l’ESO, pour la réalisation des 1000 segments de 1.5m du futur télescope de 40m.

28 Nov 2014 - 11h

  • Matthieu Gounelle (Muséum National d’Histoire Naturelle, Institut Universitaire de France)
  • Météorites - A La Recherche De Nos Origines (Un livre, Un auteur)

La probabilité n’est pas grande, mais elle existe : un jour, un bolide extraterrestre percutera la Terre. Est-ce là cependant tout ce que les météorites nous apprennent ? Matthieu Gounelle nous invite ici à réévaluer nos craintes et, à l’aune des dernières découvertes cosmo-chimiques et astrophysiques, à apprécier la richesse insoupçonnée des pierres tombées du ciel. D’où viennent-elles ?...

21 Nov 2014 - 11h

  • France Allard (ENS Lyon)
  • Very Low Mass Stars, Brown Dwarfs and Gas Giant Exoplanets

Understanding the atmospheric and evolutive properties of brown dwarfs and gas giant exoplanets have been important challenges for modelers around the world since the discovery of the first brown dwarfs in the field (Nakajima et al. 1995) and in the Pleiades cluster (Rebolo et al. 1995). The early studies of brown dwarfs have provided rich insights into atmospheric physics, with discoveries ranging from cloud formation (Tsuji et al. 1996), methane bands (Oppenheimer et al. 1995) and ammonia bands formation (Delorme et al. 2008), to the formation of quasi-molecular KI-H2 absorption (Allard et al. 2007), and to disequilibrium chemistry (Yelle & Griffith 2001). New classical 1D models yield spectral energy distribution (SED) that match relatively well that of M dwarfs, brown dwarfs and young gas giant exoplanets despite these complexities. These models have for instance explained the spectral transition from M to L, T and now Y brown dwarf spectral types (Allard et al. 2013). However, in presence of surface inhomogeneities as revealed recently for a nearby brown dwarf (Crossfield et al. 2014), the SED may well fit exactly, but the model parameters could be far from exact, e.g. with the effective temperature by several hundred kelvins too cool in the case of dusty brown dwarfs and young gas giant exoplanets !
I will review the progress achieved in reproducing the spectral properties of very low mass stars, brown dwarfs/gas giant exoplanets, and review progress in modeling more accurately their atmospheres using Radiation HydroDynamical (RHD) simulations.

14 Nov 2014 - 11h

  • Tim Morris (Durham University)
  • Adaptive Optics in the Land of the Giants

Astronomical observations made with the next generation of planned Extremely Large Telescopes hold immense potential to revolutionise our understanding of the Universe and our place within it. The scale of these optical monsters introduces problems that are not encountered on existing 8 to 10m class telescopes resulting in some form of Adaptive Optics (AO) being required to deliver even a seeing-limited focal plane. AO is not only key to optimising the light gathering power and delivering the high angular resolution images, but it also becomes fundamental to ELT operation. In this talk, I will highlight the worst of the potential effects that will be encountered when using an ELT (using the European ELT as an example), and then go on to describe how the current generation of on-sky AO demonstrators are being used to ensure that the ELTs can deliver science from (almost) day one. I will also present several results from the CANARY on-sky AO system, which was designed to demonstrate many of the untested AO modes that will be used at the E-ELT, including the very latest results showing the first ever Laser Tomographic AO (LTAO) corrected PSFs that were achieved earlier this year.

28 Oct 2014 - 11h

  • Volker Bromm (UT Austin)
  • The First Stars and Galaxies : The Run-up to the JWST

How and when did the cosmic dark ages end ? I discuss the physics of how the first stars and galaxies formed, within the context of cosmological structure formation. I will address their feedback on the pristine intergalactic medium, and describe ways to probe their signature with next generation facilities. I will identify the key processes and outline the major remaining uncertainties.

17 Oct 2014 - 11h

  • Fabien Patru (Arcetri Obs)
  • Interferometric direct imaging techniques

The detection of exo-planets remains a challenge in direct imaging in term of separation and contrast of intensity planet-star. An evolution of the imaging techniques is presented here by showing the parallel between a large telescope and a large array of telescopes (interferometer). The very high-contrast imaging is up to now achieved only on large telescopes by means of efficient adaptive optics (AO) and coronagraphic techniques, while the very high-angular resolution imaging remains only accessible to the long baseline interferometry. However, recently, these two fields converge and complement each other. The modern stellar interferometry uses adaptive optics, and new interferometric concepts appear on large telescopes, as for instance the pupil masking.
Another innovative approach is the "interferometric direct imaging". It has already been shown that a "hypertelescope" (formed of numerous telescopes) is able to produce an image directly in the focal plane of an interferometric beam combiner. We propose here a new technique of "pupil discretization" which improves the ultimate contrast of an AO-equipped telescope, simply by using a new integrated optic component based on the spatial filtering and the interferometry.

10 Oct 2014 - 11h

  • Edward Jenkins (Princeton)
  • The Development of Insights on ISM Phases

In terrestrial applications, we think of phases as distinct, homogeneous forms of matter that contrast with other states (e.g., solid, liquid, gas), and often we may consider a phase in the context of its being inside a specified volume within an otherwise heterogeneous system. This outlook applies equally well to the interstellar medium, where we can consider the segregation of material according to (1) its density and temperature, (2) level of ionization, (3) its thermodynamical properties, and (4) its molecular content. In recent times, the recognition of the effects of turbulent mixing and time-dependent phenomena have added new challenges to our comprehension of ISM phases and have increased the levels of complexity, but even so, phases still have a real meaning and we can characterize various regions in space has being dominated by material in a particular state.
We can follow the progression of ideas on the nature of ISM phases and how they have influenced our understanding of the fundamental processes that occur with diffuse matter in space. This presentation will offer a historical summary of how both theory and observations have refined our views on the nature of different phases, how they are created, how they interact with each other, and how they are distributed in space.

3 Oct 2014 - 11h

  • Sébastien Charnoz (Laboratoire AIM (Univ Paris Diderot / CEA Saclay) / IPGP)
  • Mission CASSINI :principaux résultats sur les anneaux et les satellites

Abstract : The CASSINI mission has been orbiting Saturn for 10 years now. It has revolutionized our knowledge of the Saturn’s system, in particular regarding its rings and satellites, and has revealed fundamental astrophysical processes that are at play just as well in galaxies or proto-planetary discs. I will present the main results of CASSINI regarding rings and satellites and link them to our understanding of planetary formation. I will show in particular that the rings are an intermediate step in the formation process of satellites. The rings, the satellites and the planet’s interior form an intimately coupled system. Finally, I will try to extrapolate those discoveries in the context of exoplanets.

26 Sep 2014 - 11h

  • Masami Ouchi (ICRR/IPMU, Japan)
  • Early Galaxies and Cosmic Reionization Probed by Ultra-Deep Observations

I review our ultra-deep imaging observation results of Subaru, Hubble, and ALMA, and discuss early galaxies and cosmic reionization at z 6-10. I also introduce our supplementary deep NIR spectroscopic observations for star-forming galaxies at z 1-3, and address the issues of ionization parameter evolution and galaxy feedback in the context of early galaxy formation and cosmic reionization that will be probed by the on-going deep large-area optical imaging survey of Subaru Hyper Suprime-Cam

18 Sep 2014 - 11h

  • Vernesa Smolcic (Zagreb)
  • The importance of radio-AGN feedback in massive galaxy formation : Insights from the COSMOS survey

Radio outflows of active galactic nuclei (AGN) are invoked in cosmological models as a key feedback mechanism in the latest phases of massive galaxy formation. However, from an observational point of view, the impact of such a mechanism on galaxy formation and evolution is still poorly understood. I will present our results, based on radio-selected samples at low (SDSS/NVSS and 3CRR surveys ; z<0.3) and high redshifts (COSMOS survey, z<3), that for the first time observationally test the importance of radio-mode feedback in massive galaxy formation (out to z=3). In particular, in the context of the commonly adopted blue-to-red galaxy evolution scenario we find that the two major radio AGN populations — the powerful high-excitation, and the weak low-excitation radio AGN — represent two, earlier and later, stages of massive galaxy build-up. To expand this study to higher redshifts, we developed a new method that efficiently selects weak AGN (such as Seyfert, LINER, and absorption line AGN) based only on their NUV-NIR photometry. This method allowed us to study, for the first time, the cosmic evolution of weak radio AGN out to z=3, which can directly be linked to the radio-mode feedback prediction in cosmological models.

12 Sep 2014 - 11h

  • John Silverman (IPMU, Japan)
  • Surveying the star-forming galaxy population at z=1.6 in COSMOS with Subaru/FMOS

The advent of multi-object near-infrared spectroscopic facilities is enabling large efforts to study the properties of high-redshift galaxies at the peak (z=2) of the cosmic star-formation history of the Universe. We report on our effort to use the Fiber Multi-Object Spectrograph (FMOS) on Subaru to acquire the first sample reaching over one thousand galaxies with accurate redshifts from NIR spectra having a resolution (R=2000) that cleanly identifies key diagnostic emission lines (Halpha, Hbeta, [OIII], [NII]), typically used for studying the ISM of galaxies at low redshift. Based on this sample, we present results on their star formation rates that indicate a clear “main sequence”, chemical enrichment, ionization conditions and dust properties. With the multi-wavelength resources available in COSMOS and followup ALMA observations, we can also address whether outflows are driven by internal processes and how efficient gas is being converted into stars for galaxies with heightened star formation likely related to mergers. Finally, the high target density allows us to characterize their environments and detect the likely progenitors of nearby massive clusters.

5 Sep 2014 - 11h

  • Akio Inoue (Osaka, Japan)
  • On the Intergalactic Attenuation for High-z Galaxies

Even after the cosmic reionization, neutral hydrogen still remains in the intergalactic space. These intervening hydrogen atoms absorb the radiation from high-z objects and make a numerous absorption lines, the so-called Lyman alpha forest, in the spectra of the objects. To know the absorption amount as a function of redshift is essentially important for studies of the high-z objects, for example, to predict how much reddening occurs in the spectra of the high-z galaxies, which is used as the so-called Lyman break technique. The current standard model for the intergalactic attenuation is Madau (1995). However, the intergalactic absorbers’ statistics, which is the ingredient of the model, is largely updated during two decades after Madau (1995). Here, I present an update of this kind model. I also show a preliminary result of the absorption excess in a proto-cluster environment found in a composite spectrum of galaxies behind the proto-cluster.

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