Vorträge, Seminare, Ereignisse

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H II regions, ionized nebulae associated to massive star formation, exhibit a wealth of emission lines that are the fundamental basis for estimating the chemical composition of the Universe. Heavy element abundances are particularly important because they regulate the cooling of the interstellar gas and are essential to the understanding of several phenomena such as nucleosynthesis, star formation and chemical evolution. For more than 80 years, however, a discrepancy of a factor of around two between heavy-element abundances derived with collisional excited lines (CELs) and recombination lines (RLs) has thrown our absolute abundance determinations into doubt.  The widely observed CELs are ~10,000 times brighter than RLs but exponentially dependent on temperature. Which of the lines (if any) gives the correct heavy-element abundances?
In this colloquium, I will talk about the solution we found for this problem, recently published in Nature. The best available deep optical spectra of star forming regions show evidence of the presence of temperature inhomogeneities within the gas. These inhomogeneities are concentrated in the highly ionized gas and cause the abundance discrepancy problem. This work implies that most metallicity determinations, those based on CELs, must be revised as they may be severely underestimated. The evidence indicates that this effect could be greater in regions of lower metallicity, such as the JWST high-z galaxies. Fortunately, since the temperature inhomogeneities are concentrated in the highly ionized areas of the nebulae, it is possible to correctly determine metallicities using CELs, following the proposed empirical relations.

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In the era of multi wavelength surveys of unprecedented sensitivity and spatial resolution, we are now able to map star cluster formation from the very early phases (deeply embedded in their natal giant molecular clouds) as well as study their feedback on the interstellar medium not only in the local universe but across cosmic times. Gravitational telescopes and JWST capabilities have opened a new window for cluster studies in young galaxies. I will present our initial NIRCam imaging studies of star clusters and stellar clumps conducted in lensed galaxies between redshift 1 and 6 in the fields of A2744 and SMACS0723. Our results show a rapid evolution of stellar clump stellar densities and broad age ranges that help us to reconstruct the conditions where proto-globular clusters (proto-GCs) formed. We find evidence pointing toward proto-GC formation taking place in reionisation-era galaxies, hence, becoming important candidates to aid reionisation. However, these studies are limited to rest-frame optical wavelengths. The local universe remains a fundamental laboratory for understanding how rapid star clusters can emerge from their natal giant molecular clouds, thus whether they can leak copious amount of ionising photons. I will showcase some key results obtained from our initial JWST observations of the FEAST (Feedback in Emerging extrAgalactic Star clusTers, #1783) sample of nearby galaxies. Combinations of NIR and MIR colors as well as MIR emission lines like Br_alpha and the 3.35 micron PAH band help us to fully map the star clusters from deeply embedded phases to late stages, when AGB stars dominate their colors. We find that the emergence phase is mostly missed in HST optical-NIR studies and last about 4 Myr in our study case, NGC628. I will then present recent results obtained from the analyses of FUV-optical spectroscopy along with HST imaging which help us to understand how stellar feedback in star clusters determine the rapid evolution of HII regions and regulates the star formation cycle within galaxies. These studies, conducted in the local universe, remain a fundamental laboratory for understanding cluster formation and evolution in rapidly evolving galaxies 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://zoom.us/j/94202622849pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 Professor Adamo is available for meetings by arrangement with her host, Kathryn Kreckel (Kathryn.Kreckel@uni-heidelberg.de).

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Abstract to be announced. 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://zoom.us/j/94202622849pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 Prof. Nierenberg is available for meetings by arrangement with her hosts, Robert Schmidt (rschmidt@uni-heidelberg.de) and Joachim Wambsganss (jkw@ari.uni-heidelberg.de).

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Multiple stellar populations in star clusters is a widespread phenomenon. They are observed to come in (at least) two flavours: either as multiple star formation episodes observed in young star clusters, or as multiple chemical abundance patterns observed in most old globular clusters, as well as in some intermediate-age star clusters. I will present a novel approach explaining why some clusters experience multiple star formation episodes, and how this approach allows the chemical evolution of a star cluster to be decoupled from the shape of its star formation history. This decoupling has the tremendous advantage of explaining the great diversity observed in star cluster properties, from ‘jagged’ star formation histories to smooth ones and from chemically-homogeneous clusters to inhomogeneous ones.

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Abstract to be announced. 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://zoom.us/j/94202622849pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 Prof. Wolfire is available for meetings by arrangement with his host, Melanie Chevance (chevance@uni-heidelberg.de).

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The Vera C. Rubin Observatory is approaching first light in mid-2024. Equipped with what is considered to be the world’s largest CCD camera, the Rubin Observatory will begin scanning the entire visible southern sky every few days. During its ten-year mission, billions of objects will be discovered, and the stream of alerts from difference image analysis will provide on the order of tens of millions of alerts each night. In order to compare and assess the impact on the various science objectives, extensive operational simulations are performed to help optimize the observing strategy. In the context of the microlensing subgroup of the Rubin LSST Transients and Variable Stars Science Collaboration (TVS), we show how the microlensing science case has been treated and what we can expect from different observing strategies. We will also highlight the work done as part of the ARI in-kind contribution and the opportunities for future ARI researchers.

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Abstract to be announced. 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://zoom.us/j/94202622849pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09

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To measure the extragalactic distances and consequently infer the Hubble constant (H0), several standard candles have been tested over the past decades. In this time of Hubble tension, Type-II Cepheids (T2Cs) could provide an alternative window to establish the first rung of the distance ladder in contrast to Classical Cepheids (CCs). In this regard, T2C’s Period-Luminosity (PL) & Period-Wesenheit (PW) relations show marginal to no metallicity dependence based on the spectral windows used. Hence, they may provide independent means to compute H0 and also could be advantageous distance indicators for the systems which are deprived of CCs. However, these Population-II pulsating stars were never thoroughly tested for distance estimation. In this talk, I will therefore assert the potency of T2Cs as a new avenue for the calibration of the extragalactic distance scale as compared to CCs & Tip of the Red Giant Branch (TRGB). To test this, we considered LMC as an anchor galaxy & M31 as a benchmark galaxy. In order to derive the robust PL/PW relations in the gri bands, we employed the bayesian probabilistic method which is more immune to outliers than the classical methods used in past literature studies. After further analysis to derive the final distances, we compared the results from T2Cs with CCs, TRGB and the CC’s precise results from HST photometry (Li & Riess 2021). On this account, we show that T2Cs can be used as accurate and precise probes of the extragalactic distance scale. Thus, they would be an excellent candidate for future JWST observations.

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Neutral hydrogen in the filaments of the cosmic web may be observable through emission of the Lyman-alpha line. Although luminous Lyman-alpha emitters are already an established tracer of the matter distribution in the high-redshift universe, the implications of the faint Lyman-alpha glow within the cosmic web, away from luminous emitters, are yet to be explored. In this talk, I will discuss the nature of large-scale, diffuse Lyman-alpha filaments and their detectability with recent integral field spectrographs such as VLT-MUSE, K-CWI, and HET-VIRUS. To explore this, we combine recent cosmological magnetohydrodynamical galaxy formation simulations with explicit calculation of the Lyman-alpha radiative transfer. We find that observable filaments are illuminated by Lyman-alpha photons that are emitted from the circumgalactic medium of intermediate-mass halos, rather than from the filaments themselves. These photons then escape and scatter within their surrounding, substantially boosting the Lyman-alpha signal from diffuse filaments. Our work provides a reference model for Lyman-alpha filaments, and demonstrates the importance and complexities of Lyman-alpha radiative transfer across spatial scales.

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Neutral hydrogen in the filaments of the cosmic web may be observable through emission of the Lyman-alpha line. Although luminous Lyman-alpha emitters are already an established tracer of the matter distribution in the high-redshift universe, the implications of the faint Lyman-alpha glow within the cosmic web, away from luminous emitters, are yet to be explored. In this talk, I will discuss the nature of large-scale, diffuse Lyman-alpha filaments and their detectability with recent integral field spectrographs such as VLT-MUSE, K-CWI, and HET-VIRUS. To explore this, we combine recent cosmological magnetohydrodynamical galaxy formation simulations with explicit calculation of the Lyman-alpha radiative transfer. We find that observable filaments are illuminated by Lyman-alpha photons that are emitted from the circumgalactic medium of intermediate-mass halos, rather than from the filaments themselves. These photons then escape and scatter within their surrounding, substantially boosting the Lyman-alpha signal from diffuse filaments. Our work provides a reference model for Lyman-alpha filaments, and demonstrates the importance and complexities of Lyman-alpha radiative transfer across spatial scales.

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The Hipparcos satellite project of the European Space Agency was dedicated to measuring the accurate positions of more than 100,000 stars. Doing so from space represented a fundamentally new discipline in space science. After the publication of the scientific results from the Hipparcos mission in 1997, ESA adopted the Gaia mission, a follow-on and vastly more advanced star-mapping satellite, in 2000. Gaia was launched in 2013 and continues to operate from its advantageous location at the Sun-Earth Lagrange point, L2. Gaia is measuring the positions of more than two billion stars in our Galaxy with extreme accuracy, and is contributing profoundly to many areas of astronomy. The talk will explain why the measurement of star positions is of such scientific importance, recall its history, and present some of the many areas of astronomy that are being impacted by these latest state-of-the-art measurements. 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://zoom.us/j/94202622849pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 Professor Perryman is available for meetings by arrangement with his host, Ulrich Bastian (bastian@ari.uni-heidelberg.de)

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The interstellar medium (ISM) in galaxies is ionised and heated by shock waves caused by stellar winds of massive stars and by supernova explosions. The combination of these effects can create large structures in the ISM called superbubbles, filled with hot, low-density plasma. Supernova remnants (SNRs) also act as recycling centres, which return elements processed in stars to the ISM. In addition, particles are accelerated to relativistic energies in the strong interstellar shocks. The emission from hot plasma is best studied in soft X-rays. I will present studies of SNRs and the hot phase of the ISM in our Galaxy and the nearby galaxies and discuss the physics of hot plasma, the evolution and energetics of SNRs and superbubbles, and their impact on star formation. 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://zoom.us/j/94202622849pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 Professor Sasaki is available for meetings by arrangement with her hosts, Kathryn Kreckel (Kathryn.Kreckel@uni-heidelberg.de) and Ralf Klessen (klessen@uni-heidelberg.de).

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Abstract to be announced. 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://zoom.us/j/94202622849pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 Professor de Koter is available for meetings by arrangement with his host, Maria Ramirez-Tannus (ramirez@mpia.de).

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MPIA signature speaker at KoCo

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MPIA signature speaker at KoCo

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