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20 December 2019 - 11h

  • Florence Durret (IAP and Sorbonne Universite)
  • Galaxy clusters and their environment

Clusters of galaxies are located at the intersection of cosmic filaments. I will first describe how we have found large extensions around clusters, at optical and/or X-ray wavelengths, suggesting that we are indeed detecting the cosmic web around clusters, and I will discuss some galaxy properties in one of these extended filaments.

At the cluster scale, I will then describe our searches for substructures in X-rays and show how X-ray temperature, pressure, entropy and metallicity maps can give informations on the cluster history by comparing them with hydrodynamical simulations.

Finally, I will talk about several properties of galaxies in clusters, such as galaxy luminosity functions, brightest cluster galaxies, jellyfish galaxies, and asymmetric galaxies.

6 December 2019 - 11h

  • Benoit Famaey
  • Galactic dynamics with Gaia

The Gaia mission measures the parallaxes, proper motions and radial velocities of a very large number of stars of our Milky Way galaxy, with the primary goal of uncovering its detailed structure, including its putative dark matter component, and its evolution. In this talk, I will review some of the most exciting results that have been obtained with Gaia data in terms of Galactic dynamics : these results are mostly uncovering an ever more complex picture, necessitating an upgrade of our theoretical tools to fully understand it.

29 November 2019 - 11h

  • Mélanie Heil (ESA)
  • ESA’s Enhanced Space Weather Monitoring System

ESA’s Space Situational Awareness Programme aims at protecting space and ground assets against adverse effects from space. The Space Weather Segment is focussing on such effects due to the activity of our Sun.

Monitoring of the Earth’s and Sun’s environment is an essential task for the now- and forecasting of Space Weather and the modelling of interactions between the Sun and the Earth. Due to the asymmetry and complexity of Earth’s magnetosphere, the involved particle environment and its dynamics, it is necessary to capture the state of the magnetic field and the particle distribution in a sufficiently large number of sampling points around the Earth, such that it allows state-monitoring and modelling of the involved processes with sufficient accuracy and timeliness.

ESA is implementing an enhanced space weather monitoring system, which includes the Lagrange mission to observe solar activity from the 5th Lagrange point of the Sun-Earth system and the establishment of a Distributed Space Weather Sensor System (D3S) to observe the effects of solar activity within Earth’s vicinity. Space weather instrumentation traditionally is highly miniaturised, and therefore appears to be well suited for small satellite systems, which could become competitive to the usually followed hosted payload approach while allowing for more flexibility with respect to the flown payload and orbital requirements.

I will present the current status and future plans of ESA’s Space Weather activities particularly focussing on D3S.

22 November 2019 - 11h

  • Françoise Combes (IRAP)
  • Molecular tori, black hole fueling, and feedback in nearby AGN

Recent molecular line observations with ALMA in several nearby Seyferts have revealed the existence of molecular tori, and the nature of gas flows at 10-20pc scale. At 100pc scale or kpc-scale, previous work on gravitational torques had shown that only about one-third of Seyfert galaxies experienced molecular inflow and central fueling, while in most cases the gas was stalled in rings. At higher resolution, i.e. 10-20pc scale, it is possible now to see in some cases AGN fueling due to nuclear trailing spirals, influenced by the black hole (BH) potential. This brings smoking-gun evidence for nuclear fueling. In our sample galaxies, the angular resolution of up to 80mas allows us to reach the BH-zone of influence and the BH mass can be derived more directly than with the M-sigma relation.

15 November 2019 - 11h

  • Pier Stefano Corasaniti (LUTH)
  • Galaxy Cluster Cosmology Beyond Cluster Number Counts

In the past years, dedicated survey programs have provided increasingly large samples of galaxy cluster observations which have opened the way to probing cosmology with galaxy clusters. These carry a wealth of cosmological information encoded in the cluster abundance, spatial clustering and density profile. To date cosmological constraints have been mainly inferred from cluster number count measurements. In this talk I will review recent results and motivate the use of complementary galaxy cluster observables. In particular, I will discuss the use of cluster sparsity measurements as a novel cosmological probe.

8 November 2019 - 11h

  • Pascal Tremblin (CEA Saclay)
  • Thermo-compositional diabatic convection in the atmospheres of brown dwarfs, exoplanets, and in Earth’s atmosphere and oceans

By generalizing the theory of convection to any type of thermal and compositional source terms (diabatic processes), we show that thermohaline convection in Earth’s oceans, fingering convection in stellar atmospheres, and moist convection in Earth’s atmosphere are derived from the same general diabatic convective instability. We also show that "radiative convection" triggered by the CO/CH4 transition with radiative transfer in the atmospheres of brown dwarfs is analogous to moist and thermohaline convection. We derive a generalization of the mixing-length theory to include the effect of source terms in 1D codes. We show that CO/CH4 "radiative" convection could significantly reduce the temperature gradient in the atmospheres of brown dwarfs similarly to moist convection in Earth’s atmosphere, thus possibly explaining the reddening in brown dwarf spectra. By using idealized 2D hydrodynamic simulations in the Ledoux unstable regime, we show that compositional source terms can indeed provoke a reduction of the temperature gradient. The L/T transition could be explained by a bifurcation between the adiabatic and diabatic convective transports and seen as a giant cooling crisis : an analog of the boiling crisis in liquid/steam-water convective flows.

The study of the impact of different parameters (effective temperature, compositional changes) on CO/CH4 radiative convection and the analogy with Earth moist and thermohaline convection is opening the possibility of using brown dwarfs to better understand some aspects of the physics at play in the climate of our own planet.

This mechanism, with other chemical transitions, could be present in many giant and Earth-like exoplanets. We present first results towards the simulation of this process for the CO/CO2 transition in secondary atmospheres of hot rocky exoplanets (young or irradiated) which could be applied to the primitive stages of the atmospheres of Earth, Mars or Venus.

18 October 2019 - 11h

  • Frédéric GALLIANO (AIM, CEA/Saclay, France)
  • Dust Evolution from the Perspective of Nearby Galaxies

A precise characterization of the grain properties is crucial for understanding the life cycle of the interstellar medium (ISM) and the evolution of galaxies. Nowadays, most of our knowledge of dust physics comes from studies of the Milky Way (MW). However, an increasing number of results on nearby galaxies provide unique discriminating constraints on fundamental grain processes. Indeed, nearby galaxies harbor a wider diversity of environmental conditions (metallicity, star-formation activity, etc.) than can be found in the MW. In particular, these nearby systems allow us to observe dust in extreme conditions, providing us valuable empirical information on grain evolution. They also constitute a necessary intermediate step toward understanding distant galaxies, as they are spatially resolved and have better wavelength coverage.

I will start with a general introduction, presenting the challenges in dust physics, and the recent advances in our understanding of the grain properties of the nearby Universe. I will then review several studies of the DustPedia project. This european collaboration aims to build a reference survey of ≈900 nearby, NIR-selected galaxies, observed with Herschel. I will detail the effort in modelling techniques we have carried out to provide the most accurate analysis possible of our data. I will finally present the various scaling relations and dust evolution trends derived among and within galaxies. I will discuss, in particular, the evolution of the dust-to-gas mass ratio and the fraction of aromatic feature carriers as a function of metallicity and star formation activity.

4 October 2019 - 11h

  • Jean-Luc Beuzit (LAM)
  • SPHERE, five years at the VLT

SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research in Europe) is a second-generation instrument for the ESO Very Large Telescope, dedicated to the direct detection and spectral characterization of giant extra-solar planets. SPHERE combines an extreme adaptive optics system, various coronagraphic devices and a suite of focal instruments providing imaging, integral field spectroscopy and polarimetry capabilities in the visible and near-infrared spectral ranges. The instrument has now been in operation for 5 years and has produced a harvest of leading scientific results. I will give an overview of the instrument, highlight the human adventure behind its development, review its performance and present a selection of the major results.

6 September 2019 - 11h

  • Annie Hughes (IRAP)
  • PHANGS : Star formation, feedback and chemical enrichment in nearby galaxies

The Physics at High Angular resolution in Nearby Galaxies (PHANGS) project is pursuing thee major observing programmes with ALMA, VLT/MUSE and the HST in order to study the interplay of the small-scale physics of gas and star formation with galactic structure and galaxy evolution across a representative sample of star-forming main sequence galaxies in the local Universe (d<20Mpc). With observations at high angular resolution (<100pc), the PHANGS legacy datasets provide a detailed, panchromatic view of ionised gas, stellar light, and the cold molecular gas in nearby galaxies and enable statistical studies of star formation, feedback, and chemical enrichment across different galaxy environments. In this talk, I will give an overview of the PHANGS project, and highlight our latest results for the physical conditions in the molecular gas reservoir, the star formation activity and chemical enrichment in PHANGS galaxies.

28 June 2019 - 11h

  • Peter Capak (Caltech)
  • Developing a Standard Model of Galaxies

The Physics at High Angular resolution in Nearby Galaxies (PHANGS) project is pursuing thee major observing programmes with ALMA, VLT/MUSE and the HST in order to study the interplay of the small-scale physics of gas and star formation with galactic structure and galaxy evolution across a representative sample of star-forming main sequence galaxies in the local Universe (d<20Mpc). With observations at high angular resolution (<100pc), the PHANGS legacy datasets provide a detailed, panchromatic view of ionised gas, stellar light, and the cold molecular gas in nearby galaxies and enable statistical studies of star formation, feedback, and chemical enrichment across different galaxy environments. In this talk, I will give an overview of the PHANGS project, and highlight our latest results for the physical conditions in the molecular gas reservoir, the star formation activity and chemical enrichment in PHANGS galaxies.
In this presentation Peter Capak will argue that a combination of large galaxy surveys and the latest machine learning techniques are allowing astrophysicists to develop a robust statistical model of the extra-galactic universe. If optimally constructed, this model would encapsulate all available information on the likelihood of observing a given type of galaxy as well as its distribution in space and cosmic epoch. The initial motivation for developing elements of this model was improved constraints on dark energy and dark matter, but it also contains significant information on how galaxies form and evolve. He will show how early version of this model have significantly improved photometric redshifts for weak lensing and can be used for spectroscopic target selection. He will conclude with examples of how he is using his models to optimally design observation with facilities in high demand such as Keck, ALMA, and the future JWST and what future techniques need to be developed.

21 June 2019 - 11h

  • Hendrik Hildebrandt (Alfa-Bonn)
  • Cosmological Weak Gravitational Lensing

Gravitational lensing represents a unique tool to study the dark Universe. Small distortions in the images of galaxies caused by the gravitational lensing effect of the matter distribution in the Universe can be detected over the whole sky. Measuring these coherent distortions makes dark matter structures "visible", allows us to study their growth over cosmic time, and yields cosmological insights complementary to other probes like the cosmic microwave background (CMB). Ongoing wide-field imaging surveys exploit this weak gravitational lensing technique to come up with competitive constraints on important cosmological parameters and insights on fundamental physics.

In this talk I will first introduce the basic concepts of weak gravitational lensing, review the history and challenges of weak lensing measurements, and then concentrate on recent results from the ongoing European Kilo Degree Survey (KiDS) and VISTA Kilo-degree Infrared Galaxy Public Survey (VIKING) projects. These KiDS/VIKING measurements show some tension with CMB measurements from the Planck mission when the standard cosmological model is assumed. The results will be put into context and compared to findings from the two other big cosmic shear experiments (HSC and DES). I will also present brand-new results from a Self-Organised-Map-based calibration of the KiDS+VIKING redshifts and how this influences the cosmological conclusions. Through a careful re-assessment of the HSC and DES results I will show that the discrepancies in large-scale-structure parameters we are seeing today are approaching a level of significance that is similar to the tension in the Hubble constant. Taken together this might hint at a serious problem of the standard ΛCDM paradigm in simultaneously explaining early- and late-time cosmic structure formation. I will conclude with an outlook towards the big experiments of the next decade in this field of research, Euclid and the Large Synoptic Survey Telescope that have the potential to yield some definitive answers to these questions.

14 June 2019 - 11h

  • Vianney Lebouteiller (Laboratoire AIM - CEA Saclay)
  • The interstellar medium of nearby primitive galaxies

The lack of detection of cold molecular gas in blue compact dwarf (BCD) galaxies is at variance with their intense star-formation episode. In particular, CO, often used a tracer of H2 through a conversion function, is selectively photodissociated in dust-poor environments. A potentially large fraction of H2 is thus expected to reside in the so-called CO-free gas, where it could be traced by neutral gas observed with infrared cooling lines [CI], [CII], and [OI]. Although the fraction of CO-free gas to total molecular gas is expected to be relatively large in metal-poor galaxies, a definite evidence is still lacking because of the difficulty in associating cooling lines with any given heating mechanism. The main issue at stake is to understand the role of molecular gas in the star formation process.

I will first show that the heating mechanism in the neutral gas cannot be dominated by the photoelectric effect on dust grains below a threshold metallicity due to a low abundance of dust and polycyclic aromatic hydrocarbons. I will then present results from a study on the dwarf galaxy IZw18 ( 2% solar metallicity) recently published in Lebouteiller et al. (2017). Optical and infrared lines are used to constrain the physical conditions in the HII region + HI region within a consistent photoionization and photodissociation model. We show that the HI region is entirely heated by a single ultraluminous X-ray source with important consequences on the applicability of [CII] to trace the star-formation rate and to trace the CO-free gas. We derive stringent upper limits on the size of H2 clumps that may be detected in the future with JWST and IRAM/NOEMA. We also show that the nature of the X-ray source can be constrained through the use of our models. I will conclude by proposing that star formation may be quenched in extremely metal-poor dwarf galaxies due to X-ray photoionization.

7 June 2019 - 11h

  • Nicolas Prantzos (IAP)
  • L’énergie des étoiles (une brève histoire d’astrophysique nucléaire)

je présenterai les différentes étapes qui ont mené à notre compréhension
de la source de l’énergie stellaire, depuis les premières idées d’une
origine gravitationnelle (19ème siècle), en passant par les apports de
la mécanique quantique dans les années 1920 et les découvertes de la
physique nucléaire dans les années 1930 qui ont finalement permis
d’élucider le problème. J’essaierai de placer ces développements et
leurs protagonistes dans le contexte (politique et culturel) de leur époque.

24 May 2019 - 11h

  • Lutz Wisotzki (Leibniz Institut für Astrophysik Potsdam AIP)
  • The high-redshift universe in Lyman-alpha emission

Lyman-alpha radiation is a natural signature of star-forming galaxies and has been used since long to identify high-redshift objects. I present observations with the MUSE instrument at the ESO-VLT that have revealed more than 1000 Lyman-alpha emitters, some of them extremely faint. Moreover, we find ubiquitous extended Ly-alpha emitting envelopes around individual normal (non-AGN) galaxies at redshifts z > 3. These Ly-alpha haloes indicate huge reservoirs of cold gas in the circumgalactic medium. At the sensitivity level reached by MUSE, a large fraction of the field of view is actually covered with Lya emission from redshifts 3 < z < 6. The corresponding cross-sections are comparable to those of high-column density hydrogen absorbers, suggesting that most atomic hydrogen at these redshifts has now also been detected in emission. Our observations provide direct insights into the spatial distribution of at least partly neutral gas in the circumgalactic medium of low mass galaxies at z > 3. I also discuss some implications for the demographics of high-redshift galaxies.

17 May 2019 - 11h

  • Francesco Pepe (Geneva)
  • ESPRESSO - High-fidelity spectroscopy with the VLT

ESPRESSO has started operations at the VLT on October 2018. It is the first HARPS-like spectro-velocimeter installed on a 10-m class telescope and able to collect incoherently the light of up to 4-UTs simultaneously, exploiting thus the collecting area of an equivalent 16-m telescope. ESPRESSO is designed for ultra-precise Doppler measurements and high-fidelity astronomical spectroscopy, and aims at searching and characterizing rocky extra-solar planets in the habitable zone of solar-type stars. The planet Proxima Cen b, which was recently discovered with HARPS, is a foretaste of what may be possible with ESPRESSO, but the high spectroscopic fidelity of ESPRESSO will also allow us to do transit spectroscopy of exoplanets, study the RM effect on faint objects, performing stellar spectroscopy in the milky way and in neighbouring galaxies, study the variability of physical constants, etc. In my talk I will describe the ESPRESSO instrument, its science drivers, and preliminary performances and results from the Commissioning and the first observation period.

10 May 2019 - 11h

  • Serena Viti (UCL)
  • Characterizing the dense gas in galaxies

It is now well established that chemistry in external galaxies is rich
and complex. In this talk I will give an
overview of the field of Astrochemistry, with special emphasis on its
relevance to extragalactic studies.
I will show how molecules play a key role in the formation and shaping
of galaxies. By using examples from different
regions of space, from starburst regions, to gas surrounding AGNs, I
will demonstrate how
important molecules are for the characterization of galaxies. Finally I
will present a new approach for the
interpretation of molecules using Bayesian and Machine Learning

3 May 2019 - 11h

  • John Carter (Institut d’Astrophysique Spatiale)
  • The water story of Early Mars through compositional remote sensing : lessons learned and future prospects for exploration

Water on early Mars has left chemical fingerprints which survive today as secondary "aqueous" minerals : clays, salts and other species. Their study allows piecing together the geochemical conditions on early Mars, to trace the potential past habitability of the planet and its ability to have sequestered organic matter over geologic time scales. The pervasive processes of water - rock interactions preserved at Mars are also a window into Hadean Earth, a period when conditions are thought to have been conducive to life but of which the record has been obliterated. Aqueous minerals are also prospective resources for future human missions to Mars. Since their discovery 15 years ago, a large diversity of mineral phases and geologic contexts have been found, but Mars has been slow to reveal its secrets. It is still not understood what the dominant mode of alteration was, if it was connected to a hydrological cycle as on Earth, and its potential for organic matter evolution and preservation. Future missions and instrument concepts are being prepared which will allow refined in-situ studies of the aqueous mineralogy and search for associated organics.

5 April 2019 - 11h

  • Roser Juanola-Parramon (NASA Goddard /UMBC)
  • Detecting exoplanets with the next generation of space telescopes : a technical perspective

Direct imaging of exoplanets in their habitable zone is extremely challenging due to two main factors : the proximity of the planet to the parent star and the flux ratio between the planet and the parent star, usually to the order of 10^-10 in the visible. In January 2016, NASA commissioned four Mission Concept Studies for the next Decadal Survey, which will decide which kind of mission will follow the steps of extremely successful telescopes like Hubble, and the future JWST and WFIRST. Of these four studies, two of them have as a primary scientific goal to detect and characterize exoplanets in their habitable zone.
These two missions are the Large UV-Optical-Infrared (LUVOIR) Surveyor and the Habitable exoplanet Imaging Mission (HabEx), which require large apertures and coronagraphs with active wavefront control to be able to suppress the starlight so faint planets can be detected and characterized adjacent to their parent star. The Extreme Coronagraph for Living Planet Systems (ECLIPS) is the coronagraph instrument on the LUVOIR Surveyor mission concept. It is split into three channels : UV (200 to 400 nm), optical (400 nm to 850 nm), and NIR (850 nm to 2.0 microns), with each channel equipped with two deformable mirrors for wavefront control, a suite of coronagraph masks, a low-order/out-of-band wavefront sensor, and separate science imagers and spectrographs.
The Apodized Pupil Lyot Coronagraph (APLC) is one of the baselined mask technologies to enable 10^-10 contrast observations in the habitable zones of nearby stars. The LUVOIR concept uses a large, segmented primary mirror (8- 15 meters in diameter) to meet its scientific objectives. For such an observatory architecture, the coronagraph performance depends on active wavefront sensing and control and metrology subsystems to compensate for errors in segment alignment (piston and tip/tilt), secondary mirror alignment, and global low-order wavefront errors. For the LUVOIR-A architecture (15m obscured telescope), we evaluate the sensitivity to segment-to-segment tip/tilt, piston, power (focus), astigmatism, coma, trefoil and spherical errors, and to errors induced by misalignment of the secondary mirror. I will present the latest results of the simulation of these effects and discuss the achieved contrast for exoplanet detection and characterization under these circumstances.

29 March 2019 - 11h

  • David Ehrenreich (U. Geneva)
  • Exoplanetary atmospheres at high spectral resolution

Observing transits of exoplanets with the Hubble Space Telescope in the ultraviolet has revealed spectacular atmospheric escape of strongly irradiated gas giants. This atmospheric photo-evaporation could explain the dearth of intermediate-mass planets close to their stars, as well as the valley separating two populations of super-Earths. The deposition of a tremendous amount of high-energy irradiation in the outer atmospheric layers of exoplanets should also impact their physical and chemical properties. I will review recent observations obtained wh ground-based, high-resolution spectrographs, that unveil the extreme conditions reigning in the upper atmospheres of exoplanets.

22 March 2019 - 11h

  • Coralie Neiner (LESIA, Observatoire de Meudon, France)
  • Space UV spectropolarimetry

In many domains of astrophysics, the study of magnetism and polarized light has become a new and essential tool. This has however never been done in the UV as it requires to go into space. I will present recent R&D work on UV polarimeters and current studies of space mission projects equipped with a high-resolution UV spectropolarimeter, such as Pollux for LUVOIR, Arago, or Lodestar.

15 March 2019 - 11h

  • Sebastian Kamann (Liverpool John Moores University)
  • Dynamical clues to the formation of star clusters

The star cluster population of the Milky Way provides a unique window to study the formation history of our Galaxy. The conditions of the epochs when the Milky Way built up most of its stellar mass are preserved in the star clusters we observe to date. However, the physics governing the formation of star clusters are still not entirely understood. For example, ancient globular clusters show subtle differences in the chemical compositions of their stars which appear to be absent in the clusters forming today. Does this suggest that cluster formation varies with mass or cosmic age ? In my presentation, I want to show how we can use the stellar dynamics of the clusters to answer such questions. Thanks to satellites such as Hubble or Gaia and powerful spectrographs we can nowadays study the motions of representative samples of stars in clusters of all ages. Using data from the MUSE spectrograph, we could already show that rotation played a crucial role in the formation of globular clusters and that they harbour larger populations of black holes than previously thought. We are further using the data to search for differences in the kinematics of their stellar populations. If detected, such differences put stringent constraints on the mechanisms that led to the formation of multiple populations in globular clusters.

8 March 2019 - 11h

  • Martin Crocce (IEEC-CSIC)
  • Accelerated Cosmic Expansion and the Dark Energy Survey

The striking discovery that the Cosmic expansion is not slowing down but accelerating has turned into one of the puzzles in Cosmology sparking large observational campaigns to map the Large Scale Structure and geometry of the Universe across cosmic time. I will briefly review this effort and then discuss The Dark Energy Survey (DES), a state-of-the-art large-scale galaxy survey designed to understand such acceleration by mapping 5000 deg2 measuring the positions and shapes for 300 million galaxies up to redshift 1, the light-curves of several thousand supernovae, and the masses of tens of thousands of galaxy clusters. I will present the latest cosmological results from the first year of observations, in particular those related to the combination of large-scale structure and weak gravitational lensing, how they compare with those from other datasets, and what to expect in the near future.

1 March 2019 - 11h

  • NISP Team (LAM)
  • NISP/EUCLID technical presentation and status

The NISP (Near Infrared Spectrometer and Photometer) is one of the two instruments to fly on the ESA Euclid spacecraft mid 2022. It operates in the near-IR spectral region (900-2000nm) as a photometer and spectrometer. The instrument is composed of :

  • a cold (135K) optomechanical subsystem consisting of a Silicon carbide structure, an optical assembly, a filter wheel mechanism, a grism wheel mechanism, a calibration unit and a thermal control system
  • a detection system based on a mosaic of 16 H2RG with their front-end readout electronic.
  • a warm electronic system (280K) composed of a data processing / detector control unit and of an instrument control unit that interfaces with the spacecraft via a 1553 bus for command and control and via Spacewire links for science data

We will present :

  • the Euclid spacecraft
  • the NISP final architecture, the different subsystems and the main performances
  • the NISP development plan, the test plan and the schedule
  • the NISP EM and FM integration

8 February 2019 - 11h

  • Erika Hamden (U. Arizona)
  • The FIREBall-2 UV balloon telescope and 2018 flight

In this talk, I will describe the telescope, instrument, and
flight of the Faint Intergalactic medium Redshifted Emission Balloon
(FIREBall-2). FIREBall-2 is a UV multi-object spectrograph fed by a 1
meter parabola mirror designed as a joint project between France and the
United States, with key components made at LAM (French PI- Bruno
Milliard). The instrument was designed to observe 4 pre-selected fields
and uses a UV optimized delta-doped EMCCD. The telescope flew on
September 22, 2018 from Fort Sumner, NM, as part of the fall CSBF
balloon campaign. The telescope collected data for several night hours
before being cut down. I will describe the testing, flight, and hardware
performance, along with some preliminary results and steps for the future.

1 February 2019 - 11h

  • Sera Markoff (API/GRAPPA, University of Amsterdam)
  • Imaging (and imagining) Black Holes

Black holes are one of the most exotic consequences of Einstein’s General Relativity, yet they are also very common players in the Universe, existing on scales ranging from the stellar up to beasts over a billion times more massive than our sun. Contrary to their reputation as cosmic vacuum cleaners, they actually serve as engines for extremely energetic processes, playing a major role in regulating the growth of galaxies. Some black holes also launch enormous jets of relativistic plasma that accelerate particles to energies millions of times higher than the Large Hadron Collider at CERN. Astronomers, astrophysicists and physicists all have reasons for wanting to understand black holes, yet we have been limited by the resolution of our telescopes from actually seeing one directly. This situation has changed dramatically with the coming of the Event Horizon Telescope, an Earth-sized array operating in the millimeter wavelength regime, that can actually make pictures of a couple of nearby supermassive black holes such as the one in our Galactic centre, Sgr A*, and the active galactic nucleus M87. I will briefly introduce the phenomenology of black hole accretion, and discuss some of the key problems we are still facing in terms of building a working model for these processes, and show some examples of the current cutting edge in modelling and interpretation. Along the way I will explain what the Event Horizon Telescope is, and how we anticipate the groundbreaking data from the first full run in April 2017 (note : I will not be able to show the results yet !) will help revolutionise our field and shed light on these complex environments.

25 January 2019 - 11h

  • Licia Verde (ICCUB)
  • The importance of bias

In cosmology bias is used in two different contexts. In one case it refers to systematic errors in a measurement or a determination of model’s parameters. In the other case it refers to the relation between the clustering of mass and that of observable tracers such as galaxies.
I will touch upon both aspects. I will highlight the importance of considering and modelling the effect of systematic errors and I will present a model of the halo bias in massive neutrinos cosmologies

18 January 2019 - 11h

  • Mark Sargent (Sussex)
  • Environment and interactions - How (not) to produce a starburst galaxy

Over the last 10 billion years the typical activity level of star-forming galaxies has decreased by more than an order of magnitude. Observations reveal that, at both low and and high redshift, there is a population of ’starburst’ galaxies that are significantly more active than the bulk of the rest of the population. Despite being comparatively rare, these starbursts are among the most popular targets for detailed studies of astrophysical processes, by virtue of being bright and thus readily observable. But what does it take to produce a starburst event during the peak epoch of galaxy formation at z 2, when even the average star-formation rate of the star-forming galaxy population was as high as locally observed only for the most extreme starbursting systems ?
In my talk I will present new measurements of the composition of the starburst population at z<2, in terms of its split into ’normal’ and interacting or merging galaxies. I will also review how a high star-formation efficiency - one of the trademarks of starburst events - is linked to galaxy environment based on the increasing body of literature on the interstellar medium in high-z galaxy clusters. Finally, I will discuss how measurements of host galaxy star-formation efficiency can provide clues on the interplay between starburst and AGN activity.

7 December 2018 - 11h

  • Pierre Beck (IPAG)
  • Shedding light on the darkest Solar System objects

Comets and most asteroids are extremely dark objets. They typically reflect only a few percent of the incoming light. I will discuss the nature of dark Solar System small bodies based on ground-based observations, in situ observation (i.e. VIRTIS / ROSETTA) and laboratory measurements. I will discuss in particular the case of C-type near-Earth asteroids, which are being targetted by two sample-return missions and how they might (or not) be representative of the main-belt population. Finally, I will discuss the case of cometary nuclei, possessing a peculiar absorption around 3-µm as observed by VIRTIS/ROSETTA. I will discuss how cometary nuclei relate to asteroid spectral-type and the nature of this spectral feature.

30 November 2018 - 11h

  • Chiara Caprini (APC Paris)
  • Cosmology with LISA

Gravitational waves can constitute a unique probe of both the early and late-time universe. After a general introduction to the subject, this seminar focuses on the potential of the space-based interferometer LISA to test cosmology. In particular, two aspects will be discussed : the stochastic gravitational wave background generated by sources in the very early universe, and the use of compact binaries, emitting gravitational waves, as standard sirens, i.e. to probe the energy content and the acceleration of the late-time universe.

23 November 2018 - 11h

  • Andrea Ferrara (SNS, Pise)
  • The Interstellar Medium of High Redshift Galaxies

In the last decade we have explored the cosmic depths and found a statistically significant number of galaxies well into the Epoch of Reionization. However, our physical knowledge of these pristine objects remains very scant. Investigating the internal structure, interstellar medium and evolution of early galaxies is the next challenge to understand key processes as the cosmic history of baryons, feedback, reionization and metal enrichment of the intergalactic medium, This ambitious plan can be tackled by combining a new generation of physically-rich, high resolution, zoom simulations with data in the sub-mm bands provided by ALMA. This approach will be soon strengthened by the forthcoming JWST power. I will review the present status and the open questions in the field.

16 November 2018 - 11h

  • Joel Vernet (ESO)
  • A multi-phase study of the Circum Galactic Medium in High-z radio galaxies with MUSE and ALMA

Radio galaxies (radio loud type-2 AGN) are among the most massive and luminous galaxies known at any redshift. They are found in high density environments (proto-clusters) and since the 1990s, it is known that they are surrounded by massive haloes extending to 150-200 kpc. These emission-line haloes extend well beyond the boundaries of the host galaxy, and form the link between its inter-stellar medium and the intra-cluster gas in the proto-cluster environment, i.e. the Circum Galactic Medium (CGM). They may well represent the accretion flows feeding the host galaxies with primordial gas from filamentary large-scale structures. The AGN is the flashlight illuminating and revealing these structures which play a crucial role in the galaxy formation process.
In this talk, I will present the results of an on-going VLT/MUSE and ALMA study of a sample of radio galaxies at 3<z<4.5 aimed at drawing a complete picture of the nature of these giant haloes in all possible phases : ionized, molecular, atomic, neutral.

9 November 2018 - 11h

  • Coralie Neiner (LESIA)
  • TBD


26 October 2018 - 11h

  • TBD
  • TBD


19 October 2018 - 11h

  • Vanessa Bailey (JPL)
  • Status and Potential Scientific Capabilities of the WFIRST Coronagraph Instrument

The Coronagraph Instrument (CGI) for NASA’s Wide Field Infrared Survey Telescope (WFIRST) will constitute a dramatic step forward for high-contrast imaging, integral field spectroscopy, and polarimetry of exoplanets and circumstellar disks, aiming to improve upon the sensitivity of current direct imaging facilities by 2-3 orders of magnitude. Furthermore, CGI will serve as a pathfinder for future exo-Earth imaging and characterization missions by demonstrating wavefront control, coronagraphy, and spectral retrieval in a new contrast regime, and by validating instrument and telescope models at unprecedented levels of precision. I will discuss the status of the instrument design, some of its key new technologies, and its potential science yield.

12 October 2018 - 11h

  • TBD
  • TBD


5 October 2018 - 11h

  • Benoit Neichel (LAM)
  • HARMONI au LAM : science, optique adaptative, designs, réalisations et intégrations

HARMONI est l’un des 3 instruments de première lumière qui équipera l’Extremely Large Telescope Européen, le futur télescope Européen de 39m de diamètre. HARMONI est un spectrographe à intégral de champ (IFU), mono-objet, qui observera dans la gamme visible et proche infra-rouge (de .5 à 2.4 microns). HARMONI fournira une résolution spectrale de R=3000 à R=20000, et une résolution angulaire de 60 à 4 mas. Pour exploiter pleinement la limite de diffraction de l’E-ELT, HARMONI sera équipé de deux systèmes d’Optique Adaptative (OA). Le premier est un système d’OA classique (SCAO) et le deuxième sera un système d’OA grand champ, assisté par étoiles lasers (LTAO). HARMONI s’inscrit dans la lignée d’instruments qui équipent le VLT, tels que SINFONI ou MUSE, et la première lumière est prévue pour 2025. Les cas scientifiques principaux d’HARMONI couvrent un large spectre, depuis l’étude et la caractérisation des exo-planètes, l’étude des populations stellaire dans les galaxies proches, et jusqu’aux galaxies à grand décalage vers le rouge. HARMONI regroupe un consortium de 6 laboratoires, dont 2 Français (LAM et CRAL). Les équipes du LAM sont en charge de la réalisation de plusieurs sous-systèmes, dont les analyseurs de surface d’onde pour l’optique adaptative.
Dans cette présentation, nous donnerons un statut du projet HARMONI et des développements actuellement en cours au LAM. En particulier, on détaillera quelques cas scientifiques d’intérêt pour les chercheurs du LAM, on présentera le concept d’instrument et son Optique Adaptative, on développera les designs réalisés par les équipes techniques du LAM et on abordera le planning de l’instrument, et les phases de tests qui se réaliseront au LAM. HARMONI est l’un des grands projets développé au LAM, et ce séminaire, à l’attention de tous les personnel du laboratoire, sera l’occasion de mettre en avant les contributions du LAM et d’échanger avec les personnels impliqués dans le projet.

28 September 2018 - 11h

  • Bernard Marty (CRPG Nancy)
  • TBD


14 September 2018 - 11h

  • Caroline Dorn (Univ Zurich)
  • Interior characterization in multiplanetary systems : TRAPPIST-1

I will start with a general introduction to the interior characterization of exoplanets. There are two kinds of data available for interior characterization. There are astrophysical observations that provide us planetary mass and radius for example, and there are data informed from theory or experiments. Both kinds of data are generally few with large uncertainties. By using Bayesian inference analysis, these uncertainties can be formally taken into account.
In a second part, I will focus on the specific case of TRAPPIST 1. Interior characterization traditionally relies on individual planetary properties, ignoring correlations between different planets of the same system. We explore such correlations and data specific to the multiplanetary-system TRAPPIST-1 and study their value for our understanding of their formation and evolution.

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