Latest talks

List of all the talks in the archive, sorted by date.

Thursday May 18, 2017
Prof. Caitlin Casey
University of Texas (USA)


The Universe’s largest galaxy clusters likely built the majority of their massive >10^11 M⊙ galaxies in simultaneous, short-lived bursts of activity well before virialization. The most challenging observational hurdle in identifying such pre-virialized “protoclusters” is their very large volumes, ~10^4 comoving Mpc^3 at z > 2, subtending areas ~half a degree on the sky. Thus the contrast afforded by an overabundance of very rare galaxies in comparison to the background can more easily distinguish overdense structures from the surrounding, normal density field. There are now five well-known 2 < z < 3 proto-clusters from the literature which are found to contain up to 12 dusty starbursts or luminous AGN galaxies each, a phenomenon that is unlikely to occur by chance even in overdense environments. I will discuss these in addition to some higher-redshift (4 < z < 5.5) groups, whose evolutionary fate is less clear. Measurements of DSFGs’ gas depletion times suggest that they are indeed short-lived on ~100 Myr timescales, and accordingly the probability of finding a structure containing more than 8 such systems is 0.2%, unless their ‘triggering’ is correlated on very large spatial scales, ~10 Mpc across. The volume density of DSFG-rich protoclusters is found to be comparable to all >10^15 M⊙ galaxy clusters in the nearby Universe, a factor of five larger than expected in some simulations. Some tension yet exists between measurements and simulations. However, improved observations of protoclusters over large regions of sky will certainly shed more light on the assembly of galaxy clusters, thus fundamental parameters governing cosmology, and also the role of environment in shaping the formation and evolution of galaxies.

Thursday May 11, 2017
Dr. Evanthia Hatziminaoglou
ESO, Garching (Germany)


ALMA is a submillimetre/millimetre telescope located at 5000m in the Atacama desert in Chile designed to observe at 0.32–9.5 mm (31–950 GHz), and it is expected to be the leading observatory in these wavelengths for many decades to come. ALMA has performed scientific observations since September 2011, with new capabilities being offered for each new observing cycle. The interface between ALMA and the astronomical community is provided by the ALMA Regional Centres (ARCs). The European ARC is located at ESO, Garching. In Europe, the services to the community are provided by a distributed network of ARC nodes. The European ARC network is an international, geographically dispersed structure, and consists of the central ARC at ESO, seven ARC nodes and one Centre of Expertise, distributed across Europe. It is an organised effort to provide the European ALMA user community with uniform expert support from the stage of proposal preparation through to data reduction, in order to enable the optimal usage and increase the scientific output of ALMA. The model for the European ARC nodes network will be described in terms of its organisation, communication strategies and user support. ALMA capabilities and recent ALMA results will also be summarised.
Depending on the interest of the participants, the talk can be followed by a small demo of the ALMA Observing Tool (OT) for the creation and submission of ALMA proposals, as well as the ALMA Snooping Project Interface (SnooPI), that allows PIs and Co-Is to follow their projects throughout their life-cycle.

Wednesday May 10, 2017
Dr. Vitaly Neustroev
University of Turku & University of Oulu (Finland)


According to standard evolutionary theory, cataclysmic variables (CV) evolve from longer to shorter orbital periods until a minimum period P_min is reached.
The period bouncers are such CVs that have passed 
beyond P_min and are evolving back toward longer periods, with the donor star now extremely dim.
This has long been predicted to be the 
"graveyard" and current state of 70% of all CVs, though only about a dozen of more or less robust candidates for
such period bouncer 
systems have been identified until now, out of a thousand of known CVs.
In this talk I will discuss the various methods by which such 
post period-minimum CVs can be recognized, and will also highlight recent progress in this field.

Tuesday May 9, 2017
Dr. Pascale Jablonka
Ecole Polytechnique Fédérale de Lausanne (Switzerland)


I will address the question of the formation of  the first generations of stars in the Local Group dwarf spheroidal galaxies as well as in the Milky Way halo. I will outline our latest news on the observational front focussing on the dispersion (or not) in abundance ratios, discuss LTE and NLTE treatments of the elemental abundances, and present how high resolution numerical simulations can help us understand the onset of the galaxy star formation histories.

Thursday May 4, 2017
Prof. Paola Marigo
Università di Padova (Italia)


Models of the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) stellar evolutionary phase play a critical role across astrophysics, from the chemical composition of meteorites in the pre-solar nebula up to galaxy evolution in the high-redshift Universe. In spite of its importance, the modelling of TP-AGB is still affected by large uncertainties which propagate into the field of extragalactic astronomy, impinging on the predicting power of current population synthesis models of galaxies in terms of their basic properties such as ages, masses and chemical enrichment. In this context I will review recent advances and ongoing efforts toward a physically-sound TP-AGB calibration that, moving beyond the classical use of the Magellanic Cloud clusters, combines increasingly refined TP-AGB stellar models with exceptionally high-quality data for resolved TP-AGB stars in nearby galaxies.

Tuesday May 2, 2017
Prof. Evencio Mediavilla Gradolph


The lack of detection of elementary particles that could explain dark matter and the recent detection of gravitational waves by the LIGO experiment have renewed interest in the hypothesis that dark matter can be made of Primordial Massive Black Holes (PMBH). We review very briefly the outcomes and limits of the classical MACHO experiment, used to probe the dark matter in the halo of the Milky Way from galactic microlensing, and introduce the more universal scenario of quasar microlensing. Quasar microlensing is sensitive to any population of compact objects in the lens galaxy, to their abundance and to their mass. Using microlensing data from 24 lensed quasars, we conclude that the fraction of mass in any type of MACHO is negligible outside of the 0.05 MSun<M<0.45 MSun mass range. This excludes any significant population of intermediate mass PBH. We estimate a fraction of halo mass in microlenses of 20%. The range of masses and abundances are in agreement with those expected for the stellar component. Using the mean mass estimate and some limits derived from multiwavelength microlensing observations we speculate about the stellar Present Day Mass Function.

Thursday April 27, 2017
Dr. Yiping Shu
National Astronomical Observatories, Beijing, China


We present Hubble Space Telescope (HST) F606W-band imaging observations of 21 galaxy-Lyα emitter lens candidates in the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line Lens Survey (BELLS) for GALaxy-Lyα EmitteR sYstems (BELLS GALLERY) survey. 17 systems are confirmed to be definite lenses with unambiguous evidence of multiple imaging. The lenses are primarily massive early-type galaxies (ETGs) at redshifts of approximately 0.55, while the lensed sources are Lyα emitters (LAEs) at redshifts from 2 to 3. The HST imaging data are well fit by smooth lens models consisting of singular isothermal ellipsoids in an external shear field. The Einstein radii of the BELLS GALLERY lenses are on average 60% larger than those of the BELLS lenses because of the much higher source redshifts which will allow a detailed investigation of the radius evolution of the mass profile in ETGs. With the aid of the average ∼ 13× lensing magnification, the LAEs are resolved to comprise individual star-forming knots of a wide range of properties with characteristic sizes from less than 100 pc to several kpc, rest-frame far UV apparent AB magnitudes from 29.6 to 24.2, and typical projected separations of 500 pc to 2 kpc.

Thursday April 20, 2017
Prof. Ignacio Cirac
Max-Planck-Institut für Quantenoptik


The discovery of Quantum Physics gave rise to one of the most important scientific and technological revolutions experienced by mankind. It triggered, for instance, the discovery of lasers, semiconductors, or nuclear power. In the last few years we are experiencing a second "Quantum Revolution", where the most exotic features of Quantum Physics can not only be confirmed, but also have major technological consequences. In particular, new cryptographic and computational opportunities are emerging, which will be impossible to reach with any other technology. Nowadays, there exists an extensive international effort to build quantum computers, cryptographic systems, as well as other devices. In this talk I will explain the basics of all those devices, their potential applications, as well as the status of that international effort and its prospects of giving rise to powerful technologies.

Tuesday April 11, 2017
Dr. Eric Fossat
Observatoire de la Côte d'Azur


Helioseismology is about 40 years old, still a young science. It has been a tremendous success providing many more results than initially expected, including those coming from Izana of course. Now we really know a lot of the solar internal structure and rotation.

However, one important parameter has still resisted to this investigation, the solar core rotation, which is not accessible to acoustic modes of oscillation, and helioseismlogy successes have all been obtained from acoustic modes. The reason is simple: the second type of seismic oscillations, called g modes (g for gravity, as the waves on the sea) are confined in the deepest layers of the Sun, while the observers are staying outside. These g modes that contain the information on all properties of the solar core have never been convincingly detected despite many efforts and attempts during the last forty years.

We have used a differential parameter of the acoustic modes, carefully selecteded to have a maximum sensitivity to the deepest layers and a minimum sensitivity to the surface layers, to look for its possible modulation produced by periodic motions in the solar core. The frequencies possibly accessible are very low, they correspond to periods between about half a day and two days. The advantage is that in this very low frequency range, if g modes exist, they must follow an asymptotic behaviour that makes possible a collective detection. Using a long data set (16.5 years) from the GOLF instrument onboard  the SOHO space mission, the result is the success of this search, and I will present you these asymptotic parameters, including the measurement of the core rotation within less than 1 percent uncertainty.

Tuesday April 4, 2017
Dr. Ismael Perez Fournon, Dr. Alina Streblyanska


How far can we see galaxies in the distant Universe? When are the first metals and the first dust formed?
We have now the first results on these topics (Laporte et al. 2017, ApJL, 837, 21L) based on the detailed analysis of
a gravitationally lensed Y-band dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field
cluster Abell 2744. Band 7 observations with the Atacama Large Millimeter/submillimeter Array (ALMA) indicate the proximate
detection of a significant 1 mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric
redshift of z~8. Deep X-SHOOTER spectra confirms the high-redshift identity of A2744_YD4 via the detection of Lyα emission
at a redshift z =8.38.  The association with the ALMA detection is confirmed by the presence of [O III] 88 μm emission at the
same redshift.  Although both emission features are only significant at the 4-sigma level, we argue their joint detection and
the positional coincidence with a high-redshift dropout in the Hubble Space Telescope images confirms the physical association.
Analysis of the available photometric data and the modest gravitational lensing magnification indicates A2744_YD4
has a stellar mass of ∼2 × 10^9 solar mass, a star formation rate of ∼20 solar mass_yr^‑1 and a dust mass of ∼6 × 10^6 solar mass.
We discuss the implications of the formation of such a dust mass only ≃ 200 Myr after the onset of cosmic reionization.

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