Recent Talks

We describe how a simple class of out of equilibrium, rotating and asymmetrical mass distributions evolve under their self-gravity to produce a quasi-planar spiral structure surrounding a virialized core, qualitatively resembling a spiral galaxy. The spiral structure is transient, but can survive tens of dynamical times, and further reproduces qualitatively noted features of spiral galaxies as the predominance of trailing two-armed spirals and large pitch angles. As our models are highly idealized, a detailed comparison with observations is not appropriate, but generic features of the velocity distributions can be identified to be potential observational signatures of such a mechanism. Indeed, the mechanism leads generically to a characteristic transition from predominantly rotational motion, in a region outside the core, to radial ballistic motion in the outermost parts. Such radial motions are excluded in our Galaxy up to 15 kpc, but could be detected at larger scales in the future by GAIA. We explore the apparent motions seen by external observers of the velocity distributions of our toy galaxies, and find that it is difficult to distinguish them from those of a rotating disc with sub-dominant radial motions at levels typically inferred from observations. These simple models illustrate the possibility that the observed apparent motions of spiral galaxies might be explained by non-trivial non-stationary mass and velocity distributions without invoking a dark matter halo or modification of Newtonian gravity. In this scenario the observed phenomenological relation between the centripetal and gravitational acceleration of the visible baryonic mass could have a simple explanation.

We will introduce the ERASMUS+ program that offers mobility exchanges between IAC, Czech, and Slovak research institutes and universities. The major part of the talk will be focused on giving information about the involved institutes in CZ and SK (Astronomical Institute of Czech Academy of Sciences, Department of Theoretical physics and astrophysics of Masaryk University, Astronomy department of Comenius University in Bratislava and Astronomical Institute of Slovak Academy of Sciences) and research topics investigated here, that span from hot Be stars, exoplanets, star clusters and relativistic astrophysics to meteoroids and interplanetary matter. All institutions open wide possibilities for collaboration in contemporary astrophysics but also in instrument development.

Galactic Archeology is today a vibrant field of research. The adoption and launch of the Gaia astrometric satellite by ESA has resulted in many spectroscopic Galactic surveys that aim to complement the Gaia data with information (for the fainter Gaia stars) about stellar elemental abundances, radial velocities, and stellar parameters. This results in multi-dimensional data sets which will allow us to put the Milky Way stellar populations into a much broader galactic context, eg by comparing with models and galaxies at large look-back times. In this talk I will review a selection of recent exciting developments in Galactic Archeaology found via on-going surveys as well as look to the future and see what surveys like 4MOST and WEAVE will bring.  The proposed surveys will be put into a wider context of past, on-going and future spectroscopic surveys and how this can all be combined to understand the Milky Way as a galaxy.

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.

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".

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). 

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.

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.

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.

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.