Latest talks

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


Video
Thursday November 16, 2017
Dr. David Sobral

Abstract

I will present new results regarding the first ~2 Gyrs of cosmic time using very wide-field Lyman-alpha (Lya) narrow-band surveys, including a large, matched Lya-Halpha survey to investigate how Lya and Lyman-continuum (LyC) photons escape from typical star-forming galaxies at high-redshift. We find that large Lya halos are ubiquitous in star-forming galaxies, and that the typical escape fraction of Lya and LyC photons is typically below a few percent. However, the escape fractions of Lya selected sources are significantly higher. We also find a much higher space density of very luminous Lyman-alpha emitters all the way from z~2 to z~7 than previously assumed, which we confirm spectroscopically with Keck, VLT and WHT. Many of our sources show high-ionisation lines in the rest-frame UV, and some have clear Lya blue wings. Our results also show that the steep drop in the Lya luminosity function into the epoch of re-ionisation happens only for the faint Lya emitters, while the bright ones likely ionise their own local bubbles very early on, and thus are visible at the earliest cosmic times. I will finish with new exciting ALMA detections of individual [CII] clumps at z~7 despite no dust continuum at the epoch of re-ionisation.


Video
Thursday November 2, 2017
Dr. Karsten Berger

Abstract

After a scientific career spanning over 10 years, in November 2014, I finally decided to leave scientific work behind and join a company. In this talk, I will describe the difficulties such a transition encompasses and focus on the knowledge I was able to transfer as well as the kind of skills I am now able to use in the company. I will also briefly discuss additional qualifications I obtained before moving to company work. Finally, I will introduce a collaboration between the company I currently work for "EFS GmbH" and the local university "Technische Hochschule Ingolstadt".


Video
Tuesday October 31, 2017
Dr. Martin Roth
AIP/InnoFSPEC

Abstract

Already a decade ago, the Advanced Camera for Surveys Nearby Galaxy Survey Treasury (ANGST) has provided spectacular images and photometry of individual stars in nearby galaxies, with the expectation to gain deep insight into star formation histories and the chemical evolution of galaxies. However, the known limitations of photometry have remained an obstacle to fully exploit the angular resolution of HST in analyzing resolved stellar populations in galaxies such as the sculptor group galaxy NGC300. We have selected NGC300 as the target of our MUSE GTO program at the VLT to explore the potential of IFUs for crowded field 3D spectroscopy, utilizing PSF-fitting techniques. With the input of stellar centroids obtained from the ANGST catalogue, we are demonstrating that the PampelMuse PSF-fitting tool is capable of extracting more than 500 spectra for individual stars of luminosity class I-III from a single MUSE pointing (1.5 h exposure time). These spectra are well deblended and allow for spectral type classification and the measurement of radial velocities. Next to stars of spectral types O…M, we find numerous carbon stars, blue emission line stars, LBV and symbiotic star candidates, and other rare objects. The excellent image quality and sensitivity of MUSE has also enabled the discovery of extremely faint HII regions, planetary nebulae, supernova remnants, and substructure of the diffuse ionized gas (DIG). 


Video
Monday October 30, 2017
Dr. Tom Broadhurst
Universidad del País Vasco

Abstract

I will describe cosmological simulations of Axion-like Dark Matter, motivated by string theory, providing  a well motivated cold dark matter alternative to the standard heavy particle interpretation. Standing de-Broglie scale waves and other interference effects are predicted within galaxies that we test with QSO lensing, pulsar timing and via stellar dynamics. Galaxy formation is delayed in this context relative to LCDM and examined with deep Hubble imaging of the earliest known galaxies.


Video
Thursday October 19, 2017
Prof. James Klimchuk
NASA Goddard Space Flight Center

Abstract

This fundamental question has challenged space scientists for decades. At temperatures of several million degrees, the corona is hundreds of times hotter than the solar surface, and heat cannot simply flow upward against the temperature gradient. (The same is true on other stars.) It is widely believed that the energy responsible for the extreme temperatures is extracted from stressed magnetic fields that permeate the corona. This likely occurs in the form of small impulsive energy bursts called nanoflares, but the details of how they work are still a matter of vigorous debate. Understanding these details is crucial, since the basic mechanisms are central to many phenomena--on the Sun, within the heliosphere, and throughout the universe. I will review our current understanding of the coronal heating problem from both the observational and theoretical perspectives.


Video
Wednesday October 18, 2017
Dr. Salvatore Cielo
IAP

Abstract

Mechanical feedback by jets from Active Galactic Nucei (AGN) is a key process in galaxies and galaxy clusters: the energy input from the jets (in literature often addressed as radio-mode feedback) is crucial in determining the properties of the hot gas (especially in cool-core galaxy clusters), as well as inflating the large cavities we observe in the X-ray gas. The interaction of AGN outflows (both jets and radiation) with cold gas in galactic environment  (quasar-mode feedback) can instead impact the cosmic star formation rate, as well as power galaxy-wide atomic and molecular outflows. Finally, AGN can affect its own proximity, regulating central gas accretion and giving rise to (sometimes) self-sustained feeding/feedback cycles.

I will follow the interaction of AGN with intergalactic and interstellar gas from large to small scales (radio-mode) with the use of numerical simulations. As radio-mode feedback, I will discuss the properties and the energetics​ of the hot gas bubbles inflated by multiple jet events in a galaxy ​cluster, with the aid of synthetic but realistic X-ray observations. On galactic scales, I will discuss the mechanical coupling of jets and radiation with a clumpy galactic disc, show how AGN can trigger dense and fast outflows, and briefly describe the impact on galactic star formation.


I will finally discuss "backflows" --- i.e. galaxy-wide gas circulation patterns that "flow back" to the circum-nuclear region --- as a mechanism for AGN self-regulation. I will show, complementing the simulations with a small-scale analytical model, how backflows are able to convey large amounts of cold gas to the central region, that can boost the AGN power by even a factor of ten.


Video
Monday October 16, 2017
Dr. Ruben Sanchez
The Royal Observatory Edinburgh

Abstract

MOSAIC is the proposed visible and near-infrared multi-object spectrograph (MOS) for ESO’s forthcoming ELT.  The instrument is currently in the initial project stage known as Phase A. When operational MOSAIC will give the ELT the ability to obtain spectra for large samples of faint astronomical sources which are simply out of reach of ESO’s current facilities--from stars at the very heart of the Milky Way, out to the most distant galaxies at the edge of the observable Universe. I will discuss the top science cases for MOSAIC and identify the key technical requirements for each case. I will then present the instrument concept design and architecture that comply with these requirements, and will end by outlining the next steps for the project.


Video
Tuesday October 10, 2017
Dr. Andrea Negri
IAC

Abstract

I will review my past and current research, mainly focussed on  the interactions between stellar dynamics, hot ISM, AGN feedback, black hole accretion in early-type galaxies. In particular, I have investigated the evolution of the X-ray hot halo and star formation in early type-galaxies, their correlation with galaxy shape and kinematics to explain the X-ray observed under-luminosity of flat objects and fast-rotators,their cold gas content and kinematics. Moreover I studied the effects due to AGN radiative and mechanical feedback, including positive feedback in a large sample of simulated ETGs, and the consequences of the BH sub-grid physics commonly employed in cosmological hydrodynamical simulations. Currently, I am mainly interested in both quasar and radio mode feedback and their effects on BH accretion rate and star formation. At the same time, I am working on the EAGLE and C-EAGLE simulations, studying the evolution of galaxy luminosity function with redshift. Due to large observational community at the Institute, future projects will involve the production of synthetic observations in different bands and spectral signatures from cosmological zoom-in simulations, in order to be compared with real observations.


Video
Tuesday October 3, 2017
Dr. Julio Carballo
Pontificia Universidad Católica de Chile

Abstract

The assembly history of the stellar halo of our Galaxy might be encoded in the kinematics, metallicities, ages and spatial distribution of the tidal streams, remnants of accreted galaxies. Globular clusters have also played an important role in the study of the processes that led to the formation of our Galaxy. Moreover, the dual Galactic globular cluster system is considered a manifestation of its hierarchical formation in the context of the Lambda-CDM scenario. Wide-field imaging and spectroscopy are crucial tools to unveil the remnants of their progenitor dwarf galaxies, already assimilated by the Milky Way. In this talk, I will summarize the evidence on the presence of accreted globulars in the Galactic halo, gathered during the last decades. I will also present our results probing that the surroundings of Galactic globular clusters are still one of the best places to detect and characterize tidal streams in the Milky Way halo. 


Video
Wednesday September 20, 2017
Dr. Rien van de Weygaert
Kapteyn Astronomical Institute, The Netherlands

Abstract



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