Seminars and Colloquia at ESO Garching and on the campus

December 2013

19/12/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Black holes and galaxy evolution: Does AGN activity follow or prevent star formation?
Ryan Hickox (Dartmouth College)
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Abstract

Recent years have seen remarkable advances in our understanding of how supermassive black holes form and grow over cosmic time, and how energy released by active galactic nuclei (AGN) connects the growth of black holes to their host galaxies and large-scale structures. Still a basic and essential question has remained largely unanswered: Does the fueling of AGN activity *follow* along with star formation in galaxies, or does feedback from AGN *prevent* star formation? I will argue that both scenarios take place depending on the properties of the galaxy and its dark matter halo. Specifically, I will review recent results suggesting that the long-term rate of black hole accretion is closely tied to the rate of star formation in the host, so that essentially all star-forming galaxies may be thought of as hosting an AGN after accounting for rapid stochastic variability. I will further discuss the strong evidence that in passive galaxies in massive halos, mechanical feedback from AGN serves to heat gaseous atmospheres and prevent further star formation. These results suggest that the connection between black holes and their host galaxies changes significantly as halos grow and galaxies evolve from star-forming to passive systems.

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12/12/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Galaxies as seen through the most energetic explosions in the universe
Sandra Savaglio (MPE)
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Abstract

Gamma-ray bursts (GRBs) are explosions of stars (longer than 2 seconds) or merging compact objects (neutron stars / black holes, shorter than 2 seconds). Although GRBs are the most energetic events after the Big Bang, their detection and localization are still very difficult. Systematic search during the past 17 years led to 330 spectroscopic redshifts; for about half of them, the host galaxy was studied in some detail. Despite the small numbers, their impact on our understanding of galaxies is large. GRB hosts offer the opportunity to explore regions of the universe which are observationally hostile for traditional means, due to gas and dust absorption, or to the large distance. The typical long-GRB host galaxy at low redshift is small, star-forming and metal poor, whereas explorations in recent years at intermediate-redshift have revealed the presence of more massive, dusty and chemically evolved galaxies. Finally, z>5 long-GRB hosts have given so far elusive results, indicating very small galaxies, smaller than what is reachable today with NIR deep surveys. The common factor is the stellar progenitor: in long GRBs these are very massive rare/short-lived stars, present in young regions whose redshift evolution is closely related to the star-formation history of the universe.

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05/12/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — The Quest for Dark Matter
Gianfranco Bertone (University of Amsterdam)
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Abstract

Astrophysical and cosmological observations provide compelling evidence that about 85% of all the matter in the Universe is in the form of Dark Matter, an elusive substance which is currently searched for with a variety of experimental strategies. In my talk, I will argue that we may be about to witness a pivotal paradigm shift in physics, as we set out to test the existence of some of the most promising dark matter candidates - the so called WIMPs, for Weakly Interacting Massive Particles - with a wide array of experiments, including the Large Hadron Collider at CERN and a new generation of astroparticle experiments underground and in space.

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November 2013

21/11/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — High energy neutrinos from the Cosmos? Recent results from the IceCube Neutrino Telescope
Elisa Resconi
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Abstract

The neutrino observatory IceCube is opening a new observational window to the Universe. IceCube, which has been fully constructed in the icecap at the South Pole, is taking data since Spring 2011 in full configuration. The first years of data reveled the existence of extremely high neutrinos at the PeV scale. The observed diffuse neutrino flux is with high probability of astrophysical origin. In this talk I will summarize the recent observation and discuss the prospect for point source searches.

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14/11/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — The Gaseous Environments of High-Redshift Galaxies: The CGM and ISM of Star-Forming Systems 2<z<3
Gwen Rudie (Carnegie-Princeton Fellow)
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Abstract

The gaseous component of galaxies is a crucial but poorly-constrained aspect of galaxy formation and evolution. I will present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey designed to explore both the physical properties of high-redshift galaxies and the connection between these galaxies and their surrounding intergalactic baryons. The KBSS is optimized to trace the cosmic peak of star formation (z~2-3), combining Keck/HIRES spectra of 15 hyperluminous QSOs with densely-sampled galaxy redshift surveys surrounding each QSO sightline. I will characterize the physical properties of the CGM gas through the spatial distribution, column densities, kinematics, and absorber line widths of ~6000 HI absorbers surrounding ~900 foreground star-forming galaxies within 50 kpc to 3 Mpc of a sightline. These measurements provide clear evidence of gas inflow and outflow as well as accretion shocks or hot outflows from these forming galaxies. I will compare these observations with recent theoretical predictions, highlighting discrepancies that suggest our theoretical picture of gas flows into and out of galaxies is still incomplete. I will also discuss KBSS-MOSFIRE, a rest-frame optical spectroscopic survey of galaxies in these same QSO fields. These data provide new insight into the physical properties of HII regions within these star-forming systems.

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October 2013

31/10/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Early-type galaxies: the last 10 billion years
Sugata Kaviraj (Oxford University, UK)
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Abstract

I review our current understanding of the formation of early-type galaxies (ETGs), in the context of studies that exploit rest-frame UV-optical photometry. I show that, contrary to our classical notion of them being old and passively evolving, ETGs host widespread star formation at late epochs via persistent minor merging, which contributes 20% of their stellar mass at the present day. Similarly, while our traditional view has been that ETGs are remnants of gas-rich major mergers at high redshift, I present empirical evidence that argues against major mergers as the dominant mechanism for the formation of these systems in the early Universe. Notwithstanding their apparent homogeneity today, ETGs are a rather heterogeneous population of galaxies, in which early mass growth was likely driven either by direct accretion (‘cold flows’) or minor mergers at high redshift.

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September 2013

26/09/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — The formation and evolution of the galaxy population
Simon White (MPA)
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Abstract

Recent observations of the high-redshift universe have characterized
the initial conditions for nonlinear structure formation over the full
range of scales responsible for dwarf and giant galaxies, galaxy
clusters and the large-scale cosmic web. At the same time, wide-field
spectroscopic and photometric surveys have measured the abundance and
clustering of low-redshift galaxies as a function of mass, size,
morphology, kinematic structure, gas content, metallicity, star
formation rate and nuclear activity, while deep surveys have explored
the evolution of several of these distributions to z>3.  Galaxy
population simulations aim to interpret these observations within the
LCDM structure formation paradigm, thereby constraining the complex,
diverse and heavily interconnected astrophysics of galaxy formation. I
will show that recent simulations are broadly consistent with the
galaxy abundances and clustering seen in both wide-field and deep
surveys, Such simulations provide predictions for topics as different
as galaxy-galaxy lensing, the triggering and duty cycles of AGN, and
the evolution of Tully-Fisher, mass-size and mass-metallicity
relations. They show galaxy assembly histories to be strongly
constrained by the structure formation paradigm, giving insight into
issues such as internally versus externally driven evolution, inflow
versus winds, major versus minor mergers, in situ versus ex situ star
formation, and disks versus bulges. In addition, simulations can now
be adapted to represent any chosen LCDM-like cosmology, allowing a
first assessment of whether galaxy formation uncertainties will limit
our ability to do precision cosmology with galaxy surveys.

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19/09/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Are planetary systems flat?
Scott Tremaine (Institute for Advanced Study)
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Abstract

Laplace argued, correctly, that the small inclinations of planetary orbits implied that the solar system formed from a flat disk. The observational and theoretical evidence on whether extrasolar planetary systems are flat, however, is still ambiguous. I will discuss constraints on flatness from the Kepler spacecraft and other sources; measurements of the Rossiter-McLaughlin effect in transiting planets, which show that many planetary systems have large stellar obliquities, and disk and high-eccentricity migration as competing mechanisms for the formation of hot Jupiters.

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July 2013

04/07/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — A New View of the High Energy Sky From The Nuclear Spectroscopic Telescope Array (NuSTAR)
Fiona Harrison (Caltech)
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Abstract

The Nuclear Spectroscopic Telescope Array, the first focusing
high-energy X-ray telescope in orbit, extends sensitive X-ray
observations of the sky from 3 - 79 keV, well above the band pass
where Chandra and XMM-Newton operate.  With an unprecedented
combination of sensitivity, spectral and imaging resolution, NuSTAR is
advancing our understanding of black holes, neutron stars, and
supernova remnants.  I will describe the mission, and present
highlights of science results from the first six months of science
observations.

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June 2013

27/06/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Self-Regulated Star Formation: From the Solar Neighborhood to High-Redshift Disks
Eve Ostriker (Princeton)
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Abstract

In disk galaxies ranging from our own Milky Way to high-redshift
systems, star formation takes place in very cold, dense cores, but
draws on a much larger reservoir of neutral atomic and molecular gas.
Recent surveys have spatially resolved both nearby galaxies and
high-redshift disks to establish increasingly precise empirical
correlations among gas, old stars, and the star formation rate (SFR).
Traditional single power law Kennicutt-Schmidt relations have been
refined to reveal three star-forming regimes for disks that extend
over more than six orders of magnitude in SFR.  In all regimes, gas
depletion timescales far exceed both global and local dynamical times.
To understand these empirical relations, it is necessary to consider
the physical state of the ISM, which is strongly coupled to recent
star formation through the feedback from massive stars -- including
copious UV radiation and powerful supernova blasts.  This energetic
feedback can lead to a state of self-regulated star formation.  Using
multiphase numerical simulations, we show that following the driving
and dissipation of turbulence in the warm/cold ISM, and resolving
scales down to pc in normal disks and 0.1 pc in starbursts, is
necessary to follow the detailed processes controlling SFRs.  The
equilibrium state can, however, also be captured with simple models in
which pressure powered by feedback balances gravitational confinement
of the warm/cold gas. Both numerical simulations and equilibrium
models are in remarkably good agreement with observations, and
demonstrate the importance of accurately modeling feedback in order to
understand galactic SFRs.

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20/06/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Water in space: from interstellar clouds to planet-forming disks
Ewine van Dishoeck (Leiden Observatory)
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Abstract

Water is a key molecule in the physics and chemistry of regions in which new stars and planets are born. In the 'Water in Star-forming Regions with Herschel' (WISH) Key Program, we have obtained a comprehensive set of gaseous water data toward a large sample of well-characterized protostars, covering a wide range of masses and luminosities -from the lowest to the highest mass protostars-, as well as evolutionary stages -from the earliest stages represented by pre-stellar cores to the late stages represented by the pre-main sequence stars surrounded only by disks. The data probe dynamical processes associated with forming stars and planets (outflow, infall, expansion), test basic gas-phase and gas-grain chemical processes, and reveal the chemical evolution of water into planet-forming disks and icy solar system objects such as comets. Recent Atacama Large Millimeter/submillimeter Array (ALMA) images of transitional disks revealing sites where planetesimal formation is currently taking place will be presented as well.

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06/06/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Epic Astrobiology
Caleb Scharf (Columbia University, New York)
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Abstract

The study of life, its origins, forms, and possible presence beyond the Earth is experiencing a renaissance. Much of this is driven by discoveries here, on Mars and in our solar system, and especially in the abundant and diverse population of planets around other stars. I will review some of the more interesting pieces of science, and discuss the theoretical and observational challenges that are particular for astronomy, as well as ways in which we're making progress and what we can expect from this odyssey in the near future.

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May 2013

02/05/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Direct imaging of exoplanets
Anne-Marie Lagrange (IPAG, Grenoble)
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Abstract

Most of the exoplanets known today have been discovered by indirect
techniques, based on the study of the host star radial velocity or
photometric temporal variations. The planet populations explored are
in the first 5-8 AU from the central stars, and have provided precious
information on the way planet form and evolve at such separations.
Direct imaging on 8-10 meter-class telescopes allows detection of
giant planets at larger separations (currently typically > 5-10 AU),
complementing thus indirect techniques.  So far, each of the -yet very
few- giant planets imaged provides an opportunity of unique dedicated
studies of their orbital, physical and atmospheric properties and
sometimes also on their interaction with "second generation", debris
disks. Actually, these few detections already challenge formation
theories.

I will present the results of direct imaging surveys obtained so far,
what they already tell us about giant planet formation and
evolution. Individual and emblematic cases will be detailed; they
illustrate what future instruments will routinely deliver for a much
larger number of stars. I will also point out the limitations of
direct imaging as well as the needs for further work in terms of
planet formation modelling.  I will finally present the tremendous
progress expected in this field thanks to forthcoming planet imagers
on 8-10 meter class telescopes, and on Extremely Large optical
Telescopes.

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April 2013

25/04/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Molecular gas and star formation in early-type galaxies
Martin Bureau (University of Oxford, UK)
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Abstract

Despite pervasive residual star formation, early-type galaxies are generally considered "red and dead", composed exclusively of old stars with little gas and no star formation. Here, the molecular gas content of early-type galaxies is constrained and discussed in relation to their evolution, providing a much greater understanding of the gas cycle in these objects and arguing for the continuing importance of (minor) mergers and cold gas accretion. Early-types also provide a new laboratory to study star formation, revealing unusual star-formation scaling relations.

First, nearly a quarter of local early-types are shown to possess a substantial amount of molecular gas, the necessary ingredient for star formation, independent of mass and environment. Second, a variety of molecular gas morphologies is revealed. The kinematics of the molecular gas and stars are often misaligned, implying an external gas origin in at least half of the systems in the field, while external gas accretion is shut down in clusters. Despite this, the kinematics of the molecular is often regular, allowing kinematic work ranging from Tully-Fisher studies to black hole mass measurements. Third, many objects appear to be in the process of forming regular kpc-size decoupled disks, and a star formation sequence can be sketched by piecing together multi-wavelength information. Early-type galaxies do not seem to systematically obey all our usual prejudices regarding star formation (e.g. Kennicutt-Schmidt law and far infrared-radio continuum correlation), suggesting a greater diversity of star formation processes than observed in disk galaxies. Last, a first step toward constraining the physical properties of the molecular gas in early-type galaxies is taken, by modeling the line ratios of temperature-, density- and opacity-sensitive molecules in a few objects.

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18/04/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Terzan 5: the remnant of a pristine fragment of the Galactic Bulge?
Francesco Ferraro (University of Bologna)
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Abstract

Terzan 5 is a stellar system commonly catalogued as a Globular Cluster
(GC), located in the inner Bulge of our Galaxy. Two distinct
sub-populations have been recently discovered in this system (Ferraro
et al. 2009, Nature, 462, 483). They define two well separated red
clumps in the (K, J-K) color-magnitude diagram (CMD) and show very
different iron content: ΔFe ~0.5 (such a large difference in iron
abundance has been found only in another GC-like stellar system, omega
Centauri, in the Halo of the Galaxy). Moreover, the abundance of light
elements measured in both sub-populations has been found not to follow
the typical anti-correlations observed in genuine GCs and the overall
chemical patterns of the two populations appear strikingly similar to
those of the Bulge stars (Origlia et al. 2011). These observational
results demonstrate that Terzan 5 is not a genuine GC, but a stellar
system that experienced complex star formation and chemical enrichment
histories. The strong chemical link with the Bulge, together with the
location in the inner region of it, suggest that Terzan 5 (at odds
with omega Centauri) is not the nucleus of an accreted dwarf galaxy,
but possibly the relic of one of the pristine fragments that
contributed to form the Bulge itself.

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04/04/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Cosmic Flows Project, Voyage to the Great Attractor
Helene Courtois (University of Lyon)
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Abstract

"Cosmic Flows" project is focused on producing observed galaxy distances for 30,000 galaxies with systematic errors below 2%, almost ten times the number currently known and a five-fold improvement in systematics. The resultant velocity field is providing initial conditions for constrained numerical cosmological simulations "CLUES". The observed and the simulated universe are then comparatively studied. This synergy of observations and theory distinguishes this program, and should lead to fundamental discoveries. Specifically, the program should give a definitive answer to an outstanding problem in cosmology since 1996 : the cause of the motion of 630 km/s of the CMB. On the path to this goal we are learning new informations on the dynamics of Large Scale Structures: the large coherent flows of galaxies away from voids and towards the Great Attractor region. We derive a most recent value for the Hubble constant at Ho=75 km/Mpc/s using SNIa. "Cosmic Flows" is bringing together unique expertise in radioastronomy, optical and space near-infrared surface photometry, theoretical astrophysics and numerical simulations. We tackle a frontier question: by learning our "cosmography", we look for where exactly are the Dark Energy and Dark Matter that dominate the cosmology?

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March 2013

21/03/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — The Galactic Bulge
Ken Freeman (Mount Stromlo Observatory)
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Abstract

The boxy Galactic Bulge is believed to have formed long ago through a bar-forming and bar-buckling instability of the Galactic disk. In order to study the chemical and dynamical properties of this bulge, we have acquired spectra of 28,000 red giant candidate stars towards the bulge, and I will describe the outcome of this large survey (the ARGOS survey). We are able to estimate the distances for all of these stars, and remove several thousand stars which lie in the foreground or background of the bulge. The chemical properties of the bulge stars show that the bulge-forming instability moved stars from the early thin and thick disk into the bulge. These stars are now locked into the bulge as chemically identifiable fossils of the early disks. We are not able to put useful limits on the presence of an additional classical (merger-related) bulge component in the inner Galaxy, but our kinematical data are fully consistent with the predictions of the instability formation scenario.

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14/03/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — How the Milky Way Built its Disk
Hans-Walter Rix (MPIA Heidelberg)
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Abstract

If we could map the global structure of the Milky Way's stellar disk, looking only at stars of a given age or abundance, it would be a direct route to delineating empirically how a typical large galaxy disk was built up. We have solved the problem of how to look at our own Galaxy this way, using large ground-based spectroscopic surveys. I will show how the overall radial and vertical structure of the Milky Way's disk changes as a function of stellar abundances, which may serve as proxies for stellar ages. Through comparison with disk formation simulations, I will also discuss what this may mean for the build-up of the Milky Way disk and its evolution. Slicing the Milky Way's disk into sets of such stellar mono-abundance populations is also proving a powerful way of constraining the Galactic potential.

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07/03/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Using massive clusters to probe structure formation and the first galaxies in the Universe: the CLASH project
Piero Rosati (ESO)
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Abstract

Massive galaxy clusters represent important signposts in the history of structure formation and evolution, and are also natural gravitational telescopes which are able to bring lensed primordial galaxies from the earliest epochs into comfortable reach for detailed studies. The CLASH project (Cluster Lensing And Supernova survey with Hubble) combines an HST Treasury program to obtain panchromatic 16-filter (ACS+WFC3) imaging of 25 carefully selected massive clusters, with panoramic ground-based imaging, a large spectroscopic campaign with VLT/VIMOS and other multi-wavelength observations. This program was designed to provide landmark progress in the investigation of the mass distribution of galaxy clusters, at ~0.4, specifically the measurement of dark matter and total density profile shapes, over a wide radial range and over cosmic time, thus testing distinctive predictions of the LCDM cosmological model and structure formation scenario. The homogeneity and high quality of this combined data set allows us to probe matter density profiles with unprecedented accuracy over 3 decade in radius from a combination of independent probes (lensing, X-ray, and dynamics), with a significant mitigation of systematic effects.

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February 2013

28/02/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Extreme Astrophysics with Revolutionary Radio Telescopes
Rob Fender (University of Southampton)
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Abstract

Against the background of the (mostly) Unchanging Heavens, the universe is punctuated by dramatic explosions and accretion events in which extremes of density, pressure, temperature, magnetic field and space-time curvature are reached which will be forever unattainable in any Earth-bound laboratory. Studying these events allows us to probe both the underlying physics as well as the effect of these massive injections of energy on the surrounding interstellar and intergalactic media. Such events are ubiquitously associated with radio emission, resulting from the interaction of highly-accelerated electrons with magnetic fields. In this talk I will outline how and where in the universe we use radio emission to understand the budget of explosive feedback, and how a new generation of radio telescopes en route to the Square Kilometre Array have the potential to revolutionize our understanding of extreme astrophysics.

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21/02/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Recent insights into Planet Formation
Hilke Schlichting
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Abstract

I will discuss recent insights that we have gained into planet formation from our solar system. In the first half of my talk, I will focus on the Kuiper belt, located at the outskirts of our planetary system, which provides a snapshot of earlier stages of planet formation and is therefore an ideal laboratory for testing planet formation theories. I will show how we can use the Kuiper belt size distribution to gain new insights into runaway growth and initial planetesimal sizes during planet formation and show how studying small km-sized Kuiper belt objects enables us to put our Kuiper belt into context of debris disks around other stars. In the second half of my talk, I will review dynamical models and geochemical constraints from the Earth, Moon and Mars and discuss their implications for the last stage of terrestrial planet formation.

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14/02/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — The Solaris Project: A Timing Survey For Circumbinary Planets Around Eclipsing Binary Stars
Maciej Konacki (Torun, Poland)
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Abstract

The SOLARIS project aims to detect from the ground circumbinary planets with the timing of eclipses of eclipsing binary stars. A network of four robotic 0.5-m telescopes on three continents (Australia, Africa and South America) will be established to carry out high cadence, high precision photometry of a sample of eclipsing binary stars. Three of the telescopes are already installed and the fourth one will become operational in the second half of 2013. The project's web site is www.projectsolaris.eu/. This effort is accompanied by our radial velocity (RV) survey for circumbinary planets which employs our novel iodine cell based technique tailored to provide very high precision RVs of double-lined binaries. Altogether these two efforts, targeting about 300 eclipsing binary stars, constitute the biggest ground based survey for circumbinary planets. Moreover, we expect that both these efforts will have a significant impact on the observational stellar astronomy. In particular for at least half of our sample we expect to deliver masses of the stars with an accuracy 10-1000 times better than the current state of the art.

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07/02/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Chemical and physical processes in the earliest phases of star formation
Paola Caselli (University of Leeds)
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Abstract

The initial conditions in the process of star and planet formation are to be found in pre-stellar cores, which are dense (n_H > 10^5 cm-3), cold (T < 10 K), centrally concentrated and gravitationally contracting regions embedded in molecular clouds. Knowledge of the physical structure and kinematics of pre-stellar cores is needed to put constraints on theories of star and planet formation. This requires a good understanding of the pre-stellar core chemical structure, as spectral line profiles of trace species provide the only diagnostics of the dynamics leading to star and planet formation. Because of their simple structure and quiescent nature, pre-stellar cores are also ideal laboratories in which to measure key astrophysical processes and parameters. I will review work on pre-stellar cores in low-mass star-forming regions, showing Herschel observations and how ALMA will unveil the still unexplored central few hundreds AU of pre-stellar cores, the future stellar system cradles. I'll then move to high-mass star-forming regions and show that our work on nearby pre-stellar cores has provided a way to unveil massive starless cores and test star formation theories. Cycle 0 ALMA and OT2 Herschel data will be presented.

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January 2013

31/01/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — New clues to the type-Ia supernova progenitor puzzle
Dan Maoz (Tel Aviv University)
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Abstract

Type-Ia supernovae (SNe Ia) are thermonuclear bombs in which about a solar mass of carbon and oxygen is burned into iron-peak elements. The "explosives" are apparently a white dwarf. SNe Ia are excellent cosmological distance indicators, and as such provided the first evidence that the cosmic expansion is accelerating. However, despite their confident use in cosmology, a major embarrassment remains: no one knows, based on direct evidence, what exactly is exploding. Two scenarios have been long considered for explaining how a white dwarf can ignite and explode as a SN Ia. In the "single-degenerate" picture, a white dwarf accretes matter from a companion "normal" star (i.e. a star with a classical equation of state), until approaching the Chandrasekhar limit and igniting. In the "double-degenerate" picture, a close white-dwarf binary loses energy and angular momentum to gravitational waves, until the two white dwarfs merge, thus starting the ignition and the thermonuclear runaway. However, both scenarios have theoretical and observational problems, and little or no direct evidence to support them. SN Ia rates, as a function of cosmic time and environment, can provide clues. I will show how many recent measurements are converging toward a single SN Ia "delay-time distribution" - the SN Ia rate, as a function of time, that would follow a hypothetical short burst of star formation. The emerging function is remarkably similar to what one expects from white dwarf mergers, based directly on the fundamentals of gravitational wave emission. A measurement of the Galactic binary white dwarf merger rate also suggests there may indeed be enough such mergers to serve as the SN Ia progenitors.

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24/01/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Reionisation via the Lyman-alpha line
Jamie Bolton (University of Nottingham)
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Abstract

The first luminous objects to form in the Universe produced ultra-violet photons which photo-ionised and heated the previously cold and neutral intergalactic medium (IGM). Observing the impact of the reionisation era on the IGM therefore provides us with an indirect probe of the formation and evolution of the first galaxies. Low frequency radio observations of the high redshift Universe will provide an exciting new window into this important epoch in the near future, but in the present the Lyman-alpha line (both in absorption and emission) can also inform us about the physical state of the high redshift IGM. In this talk I will briefly review existing observational constraints on the reionisation era, before going on to discuss new developments arising from observations of Lyman-alpha absorption around bright quasars at z=6-7 and the abundance of Lyman-alpha emitting galaxies approaching z=7. These measurements may be used to test existing theoretical models for reionisation, and can yield fresh insight into the timing of reionisation as well the nature of the first sources of light in the early Universe.

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17/01/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — Critical Tests of Theory of the Early Universe using the Cosmic Microwave Background
Eiichiro Komatsu
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Abstract

The Cosmic Microwave Background (CMB), the fossil light of the Big Bang, is the oldest light that one can ever hope to observe in our Universe. The CMB provides us with a direct image of the Universe when it was still an "infant" - 380,000 years old - and has enabled us to obtain a wealth of cosmological information, such as the composition, age, geometry, and history of the Universe. Yet, can we go further and learn about the primordial universe, when it was much younger than 380,000 years old, perhaps as young as a tiny fraction of a second? If so, this gives us a hope to test competing theories about the origin of the Universe at ultra high energies. In this talk I review the present status and future prospects on our quest to probe the physical condition of the very early Universe.

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10/01/13 (Thursday)
16:15, Auditorium Telescopium (ESO HQE, Garching) | ESO Garching
Munich Joint Astronomy Colloquium
Talk — The Most Massive Stars in the Local Universe
Paul Crowther (University of Sheffield)
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Abstract

The lower limit to the mass of stars is well defined, while the upper limit remains controversial. I shall summarise evidence in support of the currently accepted limit, and present recent VLT-based studies of the brightest members of young, nearby star clusters which argue for a higher limit. Consideration is given to questions of binarity using a variety of methods, while we present simulations of star clusters which argue for an upper mass limit close to 300 solar masses. The wider significance of this limit is discussed both for the integrated properties of unresolved star clusters and the possibility that pair-instability supernovae exist in the local universe, as proposed for SN 2007bi.

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