Seminars in 2023


Prof. Daniel Schaerer/ Prof. Andreas Zezas/ Dr. Konstantinos Kovlakas.

Green Pea and Bluberry galaxies meeting

The group of Dr. Jiri Svoboda is organizing a meeting with a focus on Green-Pea and Blueberry galaxies. These are low-redshift and local Universe dwarf, compact, and highly star-forming galaxies with unique properties while they are considered to be the best local analogs of early Universe galaxies. Three general talks will be given during the morning session of the seminar by Prof. Daniel Schaerer, Prof. Andreas Zezas, and Dr. Konstantinos Kovlakas. >> 10:00 -- 10:45: Daniel Schaerer, University of Geneva: "Insights on the Lyman continuum escape and the hardness of the ionizing spectra of compact star-forming galaxies". >> 10:45 – 11:30: Andreas Zezas, University of Crete: "The X-ray emission of galaxies in the context of their stellar populations". >> 11:30 -- 12:15: Konstantinos Kovlakas, Institute of Space Sciences/Barcelona: "Theoretical X-ray scaling relations and constraints on the X-ray output of distant galaxies".


Michal Bílek

What is the origin of the different kinematic morphologies of early-type galaxies?

Early-type galaxies (i.e. elliptical and lenticular) are divided into slow and fast rotators according to the appearance of their maps of line-of-sight velocity. Fast rotators show clear ordered rotation, while slow are supported mostly by velocity dispersion. I will speak about our work on investigation of the origin of this diversity. Inspired by cosmological simulations, we assumed that galaxies first form as fast rotators and then mergers transform some of them to slow rotators. We investigated the correlations of a measure of rotational support with various properties of galaxies that are sensitive to mergers. These include stellar ages, the presence of tidal features, and kinematically distinct cores. Each of these parameters is sensitive to a different type of merger and has a different lifetime. The found correlations, or their lack, together with observations of high-redshift universe, are explained the easiest, if the rotation support of early-type galaxies was decreased by multiple minor wet mergers more than 10 Gyr ago.


Sergey Popov

Magnetic field evolution of neutron stars: are there magnetars in binary systems?

In the talk I briefly discuss the present day view on the magnetic field evolution of neutron stars and its main observational appearance. Then, I focus on the possibility to find magnetars in binary systems of different kind. Possible candidates include accreting neutron stars (in particular, ultra luminous X-ray sources), gamma-ray sources, and fast radio bursts. I present a scenario in which the existence of a highly magnetized neutron star in a high-mass X-ray binary is possible at an age of a few million years.


Dr. Paolo Serra

The MeerKAT Fornax Survey: ubiquitous HI tails and clouds in the Fornax cluster

I will show first science results from the MeerKAT Fornax Survey. Our goal is to perform a detailed study of the nearby Fornax galaxy cluster in order to understand how galaxies lose their cold gas and stop forming stars in low-mass clusters (Mvir < 1e+14 Msun). We are doing so through very deep (down to ~1e+18/cm^2) and high resolution (up to ~ 1kpc and 1 km/s) MeerKAT observations of HI gas in a 1x2 Mpc^2 region centred on Fornax. Our survey started in October 2020 and is now 50% complete. These first data focus on the central region of the Fornax cluster and reveal for the first time the ubiquitous presence of tails and clouds of HI. Some of the HI is clearly being removed from Fornax galaxies as they interact with one another, with the intra-cluster medium and/or with the large-scale gravitational potential. I will present a sample of galaxies with long, one-sided, star-less HI tails (of which only one was previously known) radially oriented within the cluster and with measurable internal velocity gradients. The properties of these tails represent the first unambiguous evidence of ram pressure shaping the distribution of HI in the Fornax cluster. I will also discuss additional results on the HI mass function and the HI content of dwarf galaxies in Fornax.


Prof. Jin Koda

Molecular cloud evolution as the first step for star formation and galaxy evolution

Molecular gas and clouds host virtually all star formation, and therefore, their formation and evolution are the first step leading to star formation and galaxy evolution. On the basis of broad observational data, I will discuss how molecular gas and clouds evolve in the Milky Way and nearby spiral galaxies. In particular, I will argue for a long cloud lifetime (>~100 Myr), as opposed to the recently-suggested short lifetime (<~10-30 Myr). Simply put, we see molecular gas but don't see much atomic gas within galactic disks, even in the inter-arm regions, and thus the gas stays molecular. In this picture, star formation does not occur at the onset of gravitational collapse from atomic gas to molecular clouds, but is triggered in the long-existing molecular clouds. This view contradicts the traditional picture of the spiral density-wave theory, which predicts a rapid gas phase transition -- from atomic to molecular and then to atomic -- through spiral arm passage. Instead, the gas evolves through the coagulation and fragmentation of molecular clouds. The consequences of this revised view of cloud evolution, star formation, and galaxy evolution will be outlined. Meeting ID: 85610437259 Password: 8810 Scheduled time: 18/05/2023 14:00 CEST (12:00 UTC) Duration: 120 minutes Meeting link:


Josefa Grossschedl

Revealing the star formation history of nearby star-forming regions in 3D space and time with Gaia

With the help of Gaia, we have started to gain a better understanding of our Solar Neighbourhood, especially with regards to the 3D spatial structure of the local interstellar medium (ISM) and the distribution of young stars. However, to better understand the origin and evolution of the nearby young structures, we also need to measure their 3D space motions, allowing us to trace-back the orbits of stellar clusters and molecular clouds, to study the orbits of the subregions in our Galaxy and also the relative space motions within the complexes. I will present a method to study the 3D properties of nearby star-forming regions and to analyze the 6D phase-space of the individual compounds (clusters & clouds), using Gaia DR3 and ancillary radial velocity (RV) data. This approach allows us to reconstruct their formation history, including past feedback processes. In particular, I will present recent results for the star-forming complexes Orion and Scorpio-Centaurus, and how massive stellar feedback can be quantified in these regions. This further allows us to study the interaction of stars with the ISM, and the formation and evolution of feedback driven bubbles (e.g., Orion-Eridanus-Superbubble or Local Bubble). With this information, the star-forming regions can be put into context with local large scale structures (e.g., Radcliffe Wave, Split or Gould Belt?), and local phenomena can be compared to features in external galaxies, where the "birds-eye-view" (e.g., from JWST imaging) potentially allows an improved understanding of our own Galaxy’s structure.


Sumanta Chakraborty

Plunging into a higher dimensional black hole

In this talk I will discuss the late inspiral and then the transition regime to the plunge phase of a secondary, less massive compact object into a more massive braneworld black hole, in the context of an extreme-mass-ratio inspiral. I will show how to arrive at approximate expressions for fluxes due to slowly evolving constants of motion, such as the energy and the angular momentum, in the presence of the tidal charge inherited from the higher spacetime dimensions for an extreme-mass-ratio system. These expressions for fluxes are further used to introduce dissipative effects while modeling the inspiral to the plunge phase through the transition regime. Within this setup, I will provide a qualitative understanding of how the additional tidal charge present in the braneworld scenario may affect the timescale of the late inspiral to the plunge, in particular, by enhancing the time scale of the transition regime.


Amin Mosallanezhad

The properties of outflow generated from accretion flows

Black hole astrophysics is a rapidly growing field of study that has captured the attention of many researchers in recent years. The extreme physical conditions of black holes make them a fascinating subject of research. Black holes play a fundamental role in many active phenomena in the universe, such as active galactic nuclei, stellar-mass black holes, ultra-luminous X-ray sources, gamma-ray bursts, and stellar and galactic jets. Moreover, black hole astrophysics is closely related to other crucial topics in astrophysics. Observational evidence has established a strong correlation between the mass of the black hole and the luminosity, stellar velocity dispersion, or stellar mass in the galaxy spheroid. This correlation suggests that central supermassive black holes (SMBHs) play a critical role in the formation and evolution of galaxies. Active galactic nuclei (AGN) emit intense radiation, jets, and wind, which can spread from the interior of the galaxy to the spatial scale of the dark matter halo outside the galaxy. These outputs can interact with the interstellar medium, affecting the temperature, density, and spatial distribution of these gases, and ultimately impacting the formation of stars in the galaxy and even leading to the extinction of the galaxy. At the extra-galactic scale, the nuclear output of these active galaxies can interact with the gas in the ring galaxy medium and the galaxy's halo, thereby affecting the gas supply of the galaxy's outer gas to the galaxy, which in turn will also affect the star formation and galaxy evolution.


Alberto Urena

Ultra High Energy Cosmic Ray (UHECR) propagation modelling and comparison with experimental data

I will go through all the details of how UHECR propagation is calculated. For this it is needed to assume some kind of source with some distribution in the universe, and then follow the different mechanisms for energy losses and deviations that take place on the UHECR way to Earth. I will make particular emphasis on the assumptions needed and how realistic we can make them. Then I will present a way of comparing the result of these simulations with data obtained for the Pierre Auger Observatory (PAO) and Telescope Array (TA) through harmonic space auto- and cross-correlations.


Leandro Abaora

Signatures from clusters of stellar black holes in supercritical AGNs

Active galactic nuclei (AGNs) are powered by accretion onto supermassive black holes (SMBHs) with masses in the range 10^6—10^9 Msun. These SMBHs are fed by accretion disks radiating from the IR/optical bands to the X-rays. Different types of objects can orbit the SMBHs, including massive stars, neutron stars, clouds from broad- and narrow-line regions, and X-ray binaries. Isolated stellar mass black holes (BHs of ~10 Msun) should also be present in large numbers within the central parsec of the galaxies. These BHs are expected to form a cluster around the SMBH as a result of the enhanced star formation rate in the inner galaxy and black hole migration caused by gravitational dynamical friction. In this talk, we will explore the possibility of detecting electromagnetic signatures of a central cluster of BHs in a supercritical AGN, that is, an AGN where the accretion rate onto the central SMBH is greater than the Eddington rate. In these supercritical nuclei, the accretion disk launches powerful winds that interact with the objects orbiting the SMBH. Isolated BHs can capture matter from this dense wind, leading to the formation of small accretion disks around them. If jets are produced in these non-stellar microquasars, they might be sites of particle acceleration up to relativistic energies. These particles, in turn, should cool by different radiative processes. Therefore, the wind of the SMBH can eventually illuminate the BHs through the production of nonthermal radiation.


Paula Kornecki

Non-thermal emission in Star Forming Galaxies

Star-forming galaxies (SFGs) are weak but fascinating gamma-ray emitters. These sources harbor star-forming regions, which serve as "cribs" for particle acceleration and the production of cosmic rays (CRs). These CRs produce non-thermal radiation and give rise to a strong correlation between the star formation rate (SFR) and the radio/gamma-ray luminosity. A linear scaling between the SFR and the number of CR acceleration sites, such as supernova remnants and star clusters, coupled with particle escape, can explain this correlation. However, the nature of the CR transport processes, along with the interstellar medium conditions of the galaxies, remains poorly understood. In this presentation, I will conduct a multi-wavelength investigation of these galaxies, focusing on the gamma-ray energy range and the prospects of the next-generation Cherenkov Telescopes. We will also discuss how we can gain insights from the observed non-thermal luminosity-SFR correlation in different energy ranges.

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