Events, Seminars, Talks

Abstract
The interstellar medium of galaxies from the local to high-redshift Universe is pervaded with dust. Yet, the dominant dust formation and evolution mechanisms remain poorly constrained. Stellar sources such as asymptotic giant branch stars and supernovae are known dust producers, but the efficient dust destruction by supernova shocks could impose the need for an additional dust production source accounting for dust grains forming in situ in the ISM.   In this talk, I will review recent observational and numerical efforts that scrutinise the efficiency of supernova dust formation and destruction processes, and other dust production sources. I will also give an extensive overview of new exciting JWST observations of nearby supernovae, including the detection of a puzzling newly identified dusty structure that dominates the mid-infrared emission in the central regions of Cassiopeia A.  Thanks to the combined strengths of JWST and ALMA, we start probing the rise of metals and dust in the early Universe, where supernovae are thought to play an important role. Modelling the chemical build-up of metals and dust in these first galaxies, and in galaxies in the nearby Universe, gives us a unique perspective on the contributions of different dust sources and sinks, and on the baryonic cycling of dusty material in and out of galaxies. I will conclude my talk with a summary of exciting new observational inferences of dust across cosmic time. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 During her visit to Heidelberg, Professor de Looze will be available for meetings by arrangement with her host, Kathryn Kreckel(Kathryn.kreckel@uni-heidelberg.de).

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Studying the AGN feedback effect on the cold molecular gas of their host galaxies is key to understanding its impact on the local star formation. I will present a study of the CO(2-1) emission line distribution and kinematics in a sample of four local Seyfert galaxies with luminosities L_AGN ~ 10^44 erg/s. They were observed with ALMA, using a spatial resolution of ~100 – 400 pc, and covering up to ~10 kpc radii. Comparing the CO(2-1) observations with imaging data of [O III]lambda5007 emission lines from HST, we find that the ionized gas is generally observed in regions deficient in molecular gas, which we interpret to be caused by the AGN radiation partially destroying it. Although the kinematics of the cold molecular gas is dominated by rotation, all Seyfert galaxies present regions with double peaks in CO(2-1), which trace clouds with more complex motions. In particular, for NGC 3281 and NGC 6860, the cold molecular gas outflows were detected at the edges of their bipolar [O III] emission, surrounding it. I will also discuss my ongoing project to analyze the complex kinematics of the ionized gas in high-redshift radio galaxies (z ~ 3) obtained with JWST.

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The need for understanding the winds of Wolf-Rayet (WR) stars cannot be understated: the light of these stars, their mass-loss rates, ionization capabilities and ultimately their further evolution is all greatly affected by the behaviour of their wind. Despite WR-star winds being notoriously difficult to model, advancements on this matter have been made. One approach is using non-LTE, co-moving frame computations with the Potsdam Wolf-Rayet (PoWR) code where now hydrodynamic consistency throughout the wind domain is enforced. While already applied multiple times for the regime of hot, hydrogen-free WR stars, we now present their first wide-range application in the regime of nitrogen-rich late-type WN stars that still contain hydrogen in their spectra (WNLh type). A newly generated temperature sequence of these WNLh-star models reveals a sudden change in the wind regimes: Below 30 kK, the mass-loss rates increase significantly, while the terminal wind velocity drops strongly, accompanied with large changes in the emergent model spectra. This discontinuous behaviour greatly resembles the well-known bi-stability jump in B-supergiants. Examining the models, we discover that our obtained regime change does not correspond to the switch from Fe IV to Fe III as expected, but is linked to the higher ionization switch of Fe V to Fe IV, therefore also coinciding with higher stellar temperatures. Hence, this bi-stable behaviour occurs both due to a different cause and in a different temperature regime as the "classical" case for B-supergiants, making it a different phenomenon altogether; a new bi-stability jump for Wolf-Rayet stars.

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We aim to trace the evolution of eight edge-on star-forming disc galaxies through the analysis of stellar population properties of their (thin and thick) discs. We use Multi-Unit Spectroscopic Explorer (MUSE) observations and full-spectrum fitting to produce spatially resolved maps of ages, metallicities and [Mg/Fe] abundances and extract the star formation histories of stellar discs. Our maps show thick discs that are on average older, more metal-poor and more ?-enhanced than thin discs. However, age differences between thin and thick discs are small (around 2 Gyr) and the thick discs are younger than previously observed in more massive and more quiescent galaxies. Both thin and thick discs show mostly sub-solar metallicities, and the vertical metallicity gradient is milder than previously observed in similar studies. [Mg/Fe] differences between thick and thin discs are not sharp. The star formation histories of thick discs are extended down to recent times, although most of the mass in young stars was formed in the thin discs. Our findings show thick discs that are different from old thick discs previously observed in more massive galaxies or more quiescent galaxies. We propose that thick discs in these galaxies did not form quickly at high redshift, but slowly in an extended time. The thin discs were formed also slowly, but with a larger mass fraction at very recent times.

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Fast inward migration of planetary cores embedded in gaseous disks is a common problem in the current planet formation paradigm. Even though dust is ubiquitous in protoplanetary disks, its dynamical role in the migration history of planetary embryos has not been considered until recently. In this talk, I will show that a planetesimal embedded in a dusty disk leads to an asymmetric dust-density distribution that can exert a net torque under conditions relevant to planetary embryos up to several Earth masses. Building on the results or a large suite of numerical simulations for measuring this dust torque under a wide range of conditions, I will present the first study showing that dust torques can have a significant impact on the migration and formation history of planetary embryos. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 During his visit to Heidelberg, Prof. Pessah will be available for meetings by arrangement with his host, Maria Bergemann (bergemann@mpia.de).

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Even small-aperture (amateur) telescopes are indespensible for astronomical research. This way, deep exposures of galaxies in the local universe reveal a complexity of substructures. Here I will show selected highlights from a dedicated campaign, the HERON survey, that allowed us to investigate the formation channels of galaxies with some peculiar morphologies such as boxy halos.

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The interstellar medium plays a central role in the galaxy evolution process; it is the reservoir that fuels galaxy growth via star formation, the repository of material formed by these stars, and a sensitive tracer of internal and external processes that affect entire galaxies (e.g. accretion and feedback). In this overview talk, I will discuss how observations of the interstellar medium are shedding light on the vast range of physics and scales at play in the star formation and galaxy evolution processes, using results from recent observing campaigns with (sub)mm/radio facilities (IRAM, ALMA, JCMT, APEX) as well as large optical spectroscopic surveys (DESI). By connecting these observations with theory and simulations, a picture emerges where galaxy evolution is driven by gas availability on galactic- and molecular cloud-scales and the efficiency of the star formation process out of this gas, depending on local conditions in the interstellar medium. These results highlight the multi-scale nature of star formation and galaxy evolution, and help draw a path forward to understand mass assembly in the Universe. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 During her visit to Heidelberg, Prof. Saintonge will be available for meetings by arrangement with her host, Dominika Wylezalek (dominika.wylezalek@uni-heidelberg.de).

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Globular clusters are not the simple stellar populations we used to think they were. The vast majority of them consists of two main populations, dubbed the 1P (pristine) and 2P (polluted) populations, with distinct light-element chemical abundances. How multiple stellar populations unfold remains a riddle. A decade of observations has shown unambiguously that the fraction of 1P stars in clusters, F_1P, is a decreasing function of their present-day mass. That is, the multiple-stellar-population phenomenon is exacerbated in massive clusters. The present-day distribution of Galactic globular clusters in the (mass, F_1P) space must therefore hold clues regarding the formation of their multiple stellar populations. In this talk, I will decipher this distribution, detailing the processes and parameters shaping it.

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