Recent Talks

We employ a Bayesian method to infer stellar parameters from the PARSEC  v1.2S library of stellar evolution models and test the accuracy of these theoretical predictions. Detached eclipsing binaries are ideal for testing. We employ a compilation of 165 detached eclipsing binary systems of our galaxy and the Magellanic clouds with reliable metallicities and measurements for the mass and radius to 2 per cent precision for most of them. We complement the analysis with 107 stars that are closer than 300 pc, for which we adopted solar metallicity. The applied Bayesian analysis relies on a prior for the initial mass function and flat priors for age and metallicity, and it takes on input the effective temperature, radius, and metallicity, and their uncertainties, returning theoretical predictions for other stellar parameters of the binaries. Our research is mainly based on the comparison of dynamical masses with the theoretical predictions for the selected binary systems. We determine the precision of the models. Also, we derive distances for the binaries, which are compared with trigonometric parallaxes whenever possible. We discuss the effects of evolution and the challenges associated with the determination of theoretical stellar ages.

Black holes are a fundamental ingredient in our current understanding of galaxy formation. In the absence of their feedback, state-of-the-art numerical simulations fail to match the observed properties of massive galaxies. Effectively, within a Lambda Cold Dark Matter Universe, black holes reconcile cosmology and galaxy formation theories by regulating baryonic processes. However, despite of this widely-accepted and fundamental role, evidence of black hole regulated star formation remains elusive. I will present our observational efforts to characterize and understand the interplay between black hole activity and star formation, based on detailed stellar populations analyses. Our observations show that black hole and stellar population properties are tightly related, calling for a rich and complex observational framework where star formation, black holes and chemical enrichment evolve coupled in time.

Only once in a generation is there the opportunity to reveal the basic properties of a new galaxy type for the first time. With the advent of more sensitive instruments in the current large telescopes, an entirely new universe is being revealed, as it had never been seen before. And it is a challenging one, a low-luminosity universe that is populated by a myriad of new galaxies that are classified into new fancy families: the ultra-compact dwarfs (UCDs), the compact ellipticals (cEs) and the ultra-diffuse galaxies (UDGs). 

Despite some attempts to characterize and understand such galaxies, a recurrent topic prevails: what are they really? Are they intrinsic objects, i.e. were they formed as we see them now?; or were they initially other types of galaxies that have later evolved due to external interactions, which shaped them into what we see now? In the case of cEs, we have been lucky enough to catch some of them 'in the act', being stripped by a larger galaxy. However, at the same time, some of them have been found to be completely isolated and with no signs of interaction. In this talk, I will discuss the different pathways for cE formation and the expectations from their super massive black holes. I will also show how a similarly detailed study for all the faint families together can provide crucial clues for the galaxy evolution paradigm.

The Vlasov-Poisson system is the mean field limit of the classical N-body problem as N goes to infinity. First considered in plasma physics, it has been also used as an approach to describe self-gravitating systems. We will review the basic properties of this model, examine its catalog of stationary solutions and discuss its usefulness to describe galaxies.

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).