Wednesday Colloquium


"Searching for exceptional gravitational-wave sources in the upcoming LIGO/Virgo/KAGRA observing run"

Marek Szczepańczyk (LIGO-Virgo)

Multi-messenger Gravitational-Wave Astrophysics is the new venue for discovery; it is one of the most exciting areas in Science. The gravitational-wave observations by LIGO/Virgo/KAGRA challenge our understanding of the Universe and allow testing theories at an unprecedented level. While predicted, the first binary black hole merger and an intermediate-mass black hole are one of the exceptional sources observed so far that triggered a lot of research on their properties. The gravitational-wave detectors have significantly improved recently, and we expect daily detections in the upcoming 1.5 years' observing run. It's an excellent opportunity for discovery. I will present the preparation to observe new exceptional gravitational-wave sources. I will explain the searches, specifically those in real-time, that are crucial for multi-messenger observations. Finally, I will describe some lessons learned from the previous observing runs and the near-future prospects.


"Galaxy mergers: where are they and what are they good for?"

William Pearson (National Center for Nuclear Research, Warsaw)

Galaxy mergers underpin our current understanding of how the Universe has grown and evolved. As dark matter halos grow hierarchically, the galaxies that they host also merge. These mergers can radically change the morphologies of the interacting galaxies, throwing the material around and create and destroy finer structures. This disruption can also trigger enhanced star-formation events, and enhanced AGN activity. However, exactly when these changes occur, and how powerful they can be, is hotly contested. Thus, large samples of merging galaxies are needed to study these changes in more detail. There are a number of different ways of identifying galaxy mergers; from simply looking at the images to using the latest machine learning techniques. Through this seminar, we will look at different techniques and how we can use them to identify galaxy mergers. We will see how the more advanced techniques will allow us to explore parameter spaces that are often overlooked and find galaxy mergers in surprising ways. This talk will also discuss the ongoing and future directions of merger studies. How we can get around the truth problem: what exactly is a galaxy merger? What kinds of science we can do with merger classifications that we have now and the classifications we will be making in the next few years?


"Probing the baryon cycle of low-metallicity dwarf galaxies"

Nanni Ambra (National Center for Nuclear Research, Warsaw)

The chemical enrichment of galaxies is determined by different physical processes: stellar birth and evolution, dust growth and destruction, large-scale galactic inflows and outflows of material. Understanding the interplay of such processes is essential in order to study the build-up of metals and dust across the cosmic time, and to interpret the available and future observations (e.g. from Spitzer, JWST, ALMA). In this talk, I will review the main uncertainties affecting dust evolution in the interstellar medium of galaxies. I will then present the results of an investigation focused on low-metallicity local dwarf galaxies that takes into account recent observational constrains on their outflow efficiency, as well as other observables, i.e. metallicity, gas fraction, dust-to-stellar mass ratio, specific star formation rate, age of the main stellar population. Such a richness of information allows us to study in details the baryon cycle in these systems. In particular, I will show how the comparison between model predictions with observations allows us to identify the most relevant physical processes driving baryon evolution in local dwarf galaxies. For the first time, we also test the results for different initial mass functions of the stars, i.e. Chabrier and top-heavy.


"Time-dependent modeling of particle acceleration and cooling in blazars"

Anton Dmytriiev (North-West University, South Africa)

Flaring states of blazars are ideally suited to study the extreme physics of relativistic outflows. A thorough understanding of particle acceleration and cooling mechanisms operating in blazar jets can be achieved via physical modeling of varying multi-band flaring emission from radio up to gamma-ray range. The majority of the numerical codes developed for this task use a simplified continuous-loss description for the inverse Compton particle cooling. Such an approximation is however no longer valid in the Klein-Nishina (KN) regime. In our study, we explore the importance of non-continuous Compton cooling losses and their effect on the blazar electron spectrum and broad-band spectral energy distribution (SED) for typical physical conditions during blazar gamma-ray flares. We find that the non-continuous cooling can lead to a significant modification of the shape of the electron spectrum and SED, especially during flaring states of FSRQs characterized by high Compton dominance.


"Proto-neutron star evolution and neutrino interactions in hot and dense matter"

Micaela Oertel (LUTH, Meudon)

Neutrinos play an important role in compact star astrophysics: neutrino-heating is one of the main ingredients in core-collapse supernovae, neutrino-matter interactions determine the composition of matter in binary neutron star mergers and have among others a strong impact on conditions for heavy element nucleosynthesis and neutron star cooling is dominated by neutrino emission except for very old stars. Many works in the last decades have shown that in dense matter medium effects considerably change the neutrino-matter interaction rates, whereas many astrophysical simulations use analytic approximations which are often far from reproducing more complete calculations. In this talk I will present a scheme which allows to incorporate improved rates into simulations and show as an example results for the evolution of a proto-neutron star.