Kolloquium


The Institut für Astrophysik Kolloquium occurs weekly and provides a chance for researchers from all over the world to present exciting new results and interact with members of our department during their visit.

 

The colloquia take place on Mondays at 15:00 in the Hörsaal of the institute building in Sternwartepark, and are also streamed online at this Zoom link.

 

If you have visitors or collaborators whom you think would make great colloquium speakers, please contact any of the organizers (Ryan Leaman, Glenn van de Ven, Sudeshna Boro Saikia, Florian List, Alvaro Hacar, Núria Miret Roig

Speakers

/

  • Monday April 22: Jorryt Matthee - "How galaxies and supermassive black holes changed the early Universe: insights after 1 year of JWST"
  • Monday April 15: Roser Pello - "MOSAIC, a unique instrument for the ELT"

    Abstract: MOSAIC is the future multi-object fibre spectrograph for the ESO 39m Extremely Large Telescope (ELT), working in both the Visible and NIR domains. It is a first generation instrument, with unique capabilities in terms of multiplex, wavelength coverage and spectral resolution. While ELT first light instruments will be using only the central part of the ELT focal plane, MOSAIC is designed to cover the largest possible area (~40 arcmin²) thanks to an original stepped and tiled focal plane design which allows parallel observations in different modes. MOSAIC is optimized to achieve the best possible signal-to-noise ratio on the faintest sources, from our Galaxy to the epoch of the reionization. In this respect, it will be a privileged survey machine for the followup of sources being discovered by current and future major facilities, such as JWST, Euclid, ROMAN or SKA. I will review the main expected contributions of MOSAIC to extragalactic science, focusing on the study of the first galaxies formed in the Universe.

  • Monday March 25: Giuseppina Battaglia - "The properties of satellite galaxies in the context of their orbits around the Milky Way"
    Abstract: The Local Group hosts about 100 dwarf galaxies, i.e. galaxies with stellar masses at least one order of magnitude lower than that of the Milky Way. As the smallest galaxies and the most dark matter dominated ones that we can observe in detail, Local Group dwarf galaxies are widely considered as precious systems to shed light on the processes that drive galaxy formation and evolution at small halo masses.   Nonetheless, the majority of Local Group dwarf galaxies are found in the surrounding of a much larger system, i.e. the Milky Way or M31; this makes the knowledge of the orbits around the host  a crucial piece of information for investigating  the role of environment in shaping the dwarf galaxies' properties. In this talk I will present results from recent works, in which the exquisite astrometric data from the (early) third release of data from the ESA Gaia mission were used to provide probabilities of membership and systemic proper motions for Local Group dwarf galaxies. I will then discuss the orbital properties determined for the sub-set of about 50 dwarf galaxies found within 500 kpc from the Milky Way in the context of dwarf galaxies's group infall, tidal disruption  from the Milky Way, and possible impact on the dwarfs star formation histories, as well as discuss some of the possibilities that clean samples of member stars from Gaia data are offering. Finally, I will briefly introduce the plans for the upcoming Galactic Archaelogy surveys with the WEAVE instrument, mounted at the prime focus of the William Herschel telescope.
  • Monday March 18: Jarita Holbrook - "How Astrophysics Discriminate"

    Special colloquium within the Faculty Public Lecture Series:

    "Academia and In/Equality"

    fgga.univie.ac.at/en/inequality/

     

  • Monday March 18: Laura Magrini

    Note: Special Time 13:15

  • Monday March 11: Javier Oliveras
  • Monday March 4th: Emily Hunt
  • Monday February 26: Francisco Nogueras Lara - "The Dark Heart of the Galaxy: A Tale of Stars and Dust"

    Abstract: The heart of the Milky Way is our nearest galactic nucleus and the only one where it is possible to resolve individual stars down to milli-parsec scales. Therefore, it is a unique template for understanding other galactic nuclei and their role in galaxy formation and evolution. The Galactic centre is also the most prolific star-forming environment in our Galaxy when averaged over volume, making it a perfect laboratory to understand star formation under extreme conditions, similar to those in starburst or high-redshift galaxies. However, high crowding and extinction hinder its study, and even its morphology and kinematics are not yet entirely clear. The recent publication of new photometric and proper motion catalogues has allowed us to gain new insights into its properties. In this talk, I will describe our recent results on its stellar population, formation scenario, and morphology.

    Host: Stefan Meingast

  • Monday October 2: Philippe Bourdin - "The European Solar Telescope Project"

    Abstract:

    The EST project gives great opportunities for novel observations of the Sun at unprecedented and photon flux rates. This leads to better resolution and higher spectral capabilities when observing the lower atmospheric layers. We will discuss the current and future project phases, as well as the technical and scientific challenges.

    Host: Bodo Ziegler

     

     

  • Monday October 9: Stella Offner - "Our Lonely Sun: How Multiple Star Systems Form (or don't)"

    Abstract: 

    Most stars are born with one or more stellar companions. Observational advances over the last decade have enabled high-resolution, interferometric studies of forming multiple systems and statistical surveys of multiplicity in star-forming regions. These have yielded new insights into how such systems form and how multiplicity affects disk evolution and planetary architectures. In this talk, I will review recent observational discoveries of the youngest multiple systems. I will present the results of star cluster simulations modeling the formation and evolution of multiple systems, and I will discuss the role of dynamics and environment in setting stellar multiplicity.  Finally, I will highlight remaining numerical and observational challenges.

    Host: Núria Miret Roig

  • Monday October 16: Alyson Brooks - "Interpreting Newly Discovered Dwarf Galaxies"

    Abstract: 

    New observational surveys (e.g., Rubin's LSST, WALLABY) are enabling the discovery of hundreds of nearby dwarf galaxies.  Are we theoretically ready for what the surveys will find?  The past decade has seen tremendous progress in simulating realistic dwarf galaxies.  In this talk, I'll outline a campaign to simulate the largest suite of dwarf galaxies to date, in environments both near the Milky Way and further afield.  These high-resolution, cosmological simulations are probing dwarf galaxy formation from LMC-mass scales down into the regime of the ultra-faints for the first time.  I will highlight some of the first predictions at the low-mass edge of galaxy formation, and highlight the importance of realistic star formation when interpreting the dark matter content of dwarf galaxies.

    Host: Ryan Leaman

  • Monday October 23: Chirag Modi - "Scaling simulation-based inference for the next generation of cosmological surveys"

    Abstract:
    Simulation-based inference (SBI) is a promising approach to leverage cosmological simulations and extract information from the non-Gaussian, non-linear scales that cannot be modeled analytically. However, scaling SBI to the volumes and resolutions probed by the next generation of galaxy clustering surveys can be computationally prohibitive.  This is exacerbated by the fact that if we do not use accurate high fidelity simulations, SBI is susceptible to model misspecification. I will begin by putting this in context with discussing the sensitivity of SBI on the various components of cosmological simulations: gravity model, halo-finder and the galaxy-halo distribution models (halo-occupation distribution, HOD). Then, to overcome this computational bottleneck, I will present a new framework for cosmological analysis called Hybrid simulation-based inference (HySBI). HySBI combines perturbative methods (PT) on large scales with conditional SBI on small scales, thus learning the small-scale likelihood for a wide range of statistics using only small-volume simulations and drastically reduces computational costs. As a proof-of-principle, I will show results of using HySBI to constrain cosmological parameters on dark matter density fields using both the power spectrum and wavelet coefficients, finding promising results that significantly outperform classical PT methods. Finally, I will discuss a roadmap for the next steps necessary to implement HySBI on actual survey data, including consideration of bias, systematics, and customized simulations.

    Host: Oliver Hahn

  • Monday October 30: Paola Testa - "Observational signatures of coronal heating mechanisms in solar active regions"

    Abstract
    The details of the physical mechanisms responsible for heating the solar outer atmosphere to millions of degrees are still poorly understood. 
    Recent high resolution observations of the solar atmosphere (e.g., with SDO, Hinode, IRIS, SST) provide new powerful diagnostics of the coronal heating mechanisms. I will discuss how these new observations have enabled significant advances in our understanding of coronal heating properties in active regions. 
    I will especially focus on how high spatial, spectral, and temporal resolution coordinated observations of the chromosphere, transition region and corona, when coupled with state-of-the-art (1D/3D) models, can provide tight constraints on heating properties.


    Host: Manuel Guedel

  • Monday November 6: John Tobin - "The cradles of star and planet formation: disks, multiplicity, and stellar masses of low to intermediate-mass protostars"

    Abstract:  

    The formation of disks and multiple star systems are integral parts of the star and planet formation process. Most stellar mass must be accreted through a disk, disks are the future sites of planet formation, and disks will also give rise to companion stars. Large surveys of protostars in the nearby star forming regions are being conducted (with resolutions as fine as 5 au) to characterize the disk radii, disk masses, disk structure, and the frequency of multiplicity throughout the protostellar phase. The measured multiplicity properties will be discussed, along links back to their formation mechanisms. Protostellar disks appear to be systematically more massive that the proto-planetary disks, but have substructure less frequently than proto-planetary disks. Protostar mass measurements are beginning to become available for many 10s of sources, enabling their measurements to be compared to predictions for mass functions. Thus, the combined results from surveys of protostars bring us closer to unlocking the physics driving various aspects of star and planet formation.

    Host: Alvaro Hacar

  • Monday November 13: Sergio Torres Flores - "The role of galaxy interactions in compact groups of galaxies"

    Abstract:

    Compact groups of galaxies are associations of three to six galaxies, located in a very small volume, where the separation between them is of the order of the diameters of the galaxies. Given that, galaxy-galaxy interactions and mergers are a common phenomena in compact groups of galaxies, transforming these systems into ideal laboratories to study galaxy evolution. Indeed, these strong interaction events can transform the morphological, kinematical and physical properties of galaxies. In this context, in this talk I will present a morphological analysis developed for a sample of galaxies located in 340 compact groups. We found a peculiar galaxy population, which has a smaller effective radius than galaxies located in less dense environments, indicating that the environment is playing a relevant role in the evolution of galaxies in compact groups. In addition, I will present a MUSE analysis on the merging compact group HCG 31, where we found perturbed kinematics and perturbed metallicity distributions. Finally, I will present some recent results associated with a search for vertical perturbations in local galaxies, which are typically associated with galaxy-galaxy interactions events. Thanks to the use of 3D Fabry-perot data, we found vertical perturbations which are consistent with high resolution simulations.

    Host: Bodo Ziegler

  • Monday November 27: Scott Lucchini - "Properties of the Magellanic Corona Model for the formation of the Magellanic Stream"

    AbstractWhen viewing the Large and Small Magellanic Clouds (LMC, SMC) in HI 21-cm emission, we see much more than the galaxies themselves. The Magellanic Stream, a massive structure comprised of intertwined, multiphase, gaseous filaments, trails behind the Clouds covering over 200 degrees on the sky. While previous models of the Stream's formation have shown us that many of its properties can be reproduced through interactions between the Magellanic Clouds, two puzzles remain - the large amount of ionized gas associated with the Magellanic System, and the high mass of the LMC. To solve both these outstanding discrepancies simultaneously, we introduce the Magellanic Corona. This warm, ionized circumgalactic medium should surround the LMC as it interacts with the SMC and the Milky Way. Recent observations detecting the Magellanic Corona around the LMC today provide further evidence for a high LMC mass and this leads to strong implications for the history of the Magellanic Clouds. I will present simulations of the formation of the Magellanic Stream including the Magellanic Corona in which we are able to account for both the neutral and ionized components of the Stream while also reproducing the present-day positions and velocities of the LMC and the SMC in their motion around the Milky Way. Upon inclusion of the Magellanic Corona, we find a new family of orbital histories for the Clouds that result in the neutral Stream being significantly closer than previous models predicted. I will present these new models and discuss some of the many implications of this new paradigm for the Magellanic Stream.

    Host: Cameren Swiggum

  • Monday December 4: John Peacock - "Galaxy formation in other universes"

    Abstract:

    The outstanding puzzle of fundamental cosmology is the cosmological constant: an effective vacuum density that is tiny by comparison with predictions based on quantum physics. In 1987, Steven Weinberg suggested that this puzzle might be resolved by observer selection: natural large values for the vacuum density would suppress cosmological structure formation, so there would be no star formation in galaxies, and hence no observers. I will describe recent attempts to investigate this idea in detail, taking hydrodynamical simulation codes that succeed in modelling galaxy formation in our observed universe, and applying them to cosmologies with much larger cosmological constants. I will also contrast the simulation results with the predictions of a simplified analytic model for cosmic star formation. Different approaches to this problem yield somewhat different answers, but are in qualitative agreement: raising the cosmological constant does reduce the global efficiency of star formation, meaning that such models are less likely to be experienced by observers. But this suppression is relatively slow, so that cosmological constants more than 10 times the observed value would still form stars efficiently. Thus our observed universe has a vacuum density that is small compared with the value that would be typical in Weinberg’s model, and the question is whether this could be a statistical fluctuation that is not too rare.

    Host: Oliver Hahn

  • Monday December 11: Claudia Paladini - "Stellar surfaces through the looking-glass"

     

    Abstract

    Stellar convection plays an important role in many astrophysical processes, including energy transport, pulsation, dynamos and winds onevolved stars. A direct characterization of convective structures in terms of size, contrast, and life-span is quite challenging because stars are still pretty far and convective patterns are small. Most of our knowledge about stellar convection comes from studying the Sun. On the surface of our star a couple of millions of convective cells are observed, each one with a size of about 2000 km. Following predictions dating back to the ’70, the surface of evolved stars (or a Sun at later evolutionary stage) is expected to be populated by only a few large convective cells several tens of thousand times the size of the solar ones. Such predictions were confirmed at the end of last decade  by direct observations of the stellar surface of the low mass Asymptotic Giant Branch Stars pi1 Gruis. More recently the models are being challenged when it comes to more massive objects like the Red Supergiants. In this talk I will review the recent results obtained using high angular resolution techniques to resolve the surface of stars, and I will discuss the various scenarios used to interpret the images. Are we really looking at convection? 

    Host: Josef Hron

     

     

  • Monday January 8: Quentin Changeat - "Atmospheric variability in an exoplanet"

    Abstract: 


    Observations of exoplanet atmospheres have not yet been able to infer weather patterns. While those are predicted from theoretical modeling, such signatures are difficult to observe due to the low SNR from past instruments and the lack of repeated observations. In a recent study, we utilize repeated observations of an ultra-hot Jupiter, WASP-121b, to study the variability of its atmosphere. Crucially, we detect significant differences between the observations. The observed variability manifests as: i) shift of the 'hotspot' offset between two phase-curves and ii) varying spectral signatures in the transits and eclipses. In this presentation, we will see how constraints inferred from modern atmospheric retrievals can be used to inform high-resolution dynamics calculations of weather patterns on ultra-hot Jupiters. The presented simulations are tailored to WASP-121b atmosphere, showing that the observed variability is consistent with quasi-periodic weather patterns.

    Host: Simon Schleich

  • Monday January 22: Edwin Kite - "Mars Climate Evolution: Is Small Planetary Size Fatal For Long-term Habitability?"

    AbstractThe surface of Mars appears sterile today, but was habitable in the past. What are the necessary and sufficient conditions for this environmental catastrophe? I will review the constraints on the last 3.5 billion years of Mars' long-term drying trend, and models to explain those observations. New data suggests important roles loss of non-CO2 greenhouse forcing, and also a renewed focus on carbonate formation. I will conclude by suggesting methods by which humans could restore habitability to Mars' surface in the near future.

    HostManuel Guedel

  • Monday January 29: Giuseppina Battaglia - "The properties of satellite galaxies in the context of their orbits around the Milky Way"

    Abstract

    The Local Group hosts about 100 dwarf galaxies, i.e. galaxies with stellar masses at least one order of magnitude lower than that of the Milky Way. As the smallest galaxies and the most dark matter dominated ones that we can observe in detail, Local Group dwarf galaxies are widely considered as precious systems to shed light on the processes that drive galaxy formation and evolution at small halo masses. Nonetheless, the majority of Local Group dwarf galaxies are found in the surrounding of a much larger system, i.e. the Milky Way or M31; this makes the knowledge of the orbits around the host a crucial piece of information for investigating the role of environment in shaping the dwarf galaxies' properties. In this talk I will present results from recent works, in which the exquisite astrometric data from the (early) third release of data from the ESA Gaia mission were used to provide probabilities of membership and systemic proper motions for Local Group dwarf galaxies. I will then discuss the orbital properties determined for the sub-set of about 50 dwarf galaxies found within 500 kpc from the Milky Way in the context of dwarf galaxies's group infall, tidal disruption from the Milky Way, and possible impact on the dwarfs star formation histories, as well as discuss some of the possibilities that clean samples of member stars from Gaia data are offering. Finally, I will briefly introduce the plans for the upcoming Galactic Archaelogy surveys with the WEAVE instrument, mounted at the prime focus of the William Herschel telescope.
    Host: Ryan Leaman
     
     
  • Monday February 5: Eros Vanzella - "Exploring the distant Universe with cosmic telescopes"

    AbstractThe search for the first galaxies and stars and the role they played during the cosmic hydrogen reionization is now entering an exciting era, particularly with the unprecedented capabilities offered by the James Webb Space Telescope (JWST). With improved angular resolution compared to the Hubble Space Telescope and extended wavelength coverage, JWST, positioned at the focal point of cosmic lenses (telescopes exploiting strong gravitational lensing), allows us to explore new regimes characterized by low luminosity, small size, and large distances. JWST marks a transformative moment in the study of the distant Universe, witnessing new high redshift domain and
    delving into parsec-scale star-formation processes at cosmological distances and eventually probing the formation of globular clusters.

     

    Host: Glenn van de Ven