Vorträge, Seminare, Ereignisse

Abstract
Massive stars are important in many astrophysical contexts. They dominate the energy and momentum budget of the interstellar medium and they enrich their surroundings with newly processed chemical elements, which constitute the building blocks of planets and life. Most massive stars are found in close binary systems and will interact with their companion during their lifetime, resulting in a variety of exotic products including X-ray binaries and gravitational wave sources. However, it is very challenging to understand the formation mechanism of massive stars and the origin of their high multiplicity because of their very short formation timescales, large distances, and them being embedded in their natal clouds. Additionally, more than half of all stars and planetary systems form in massive star forming regions where they are exposed to intense UV radiation from the nearby massive stars. Thanks to the unprecedented capabilities of JWST, we can now study the physical and chemical properties of proto-planetary disks in massive star-forming regions. 

In this colloquium I will present recent results concerning the formation of massive stars, including the disk and photospheric properties of pre-main sequence stars and the evidence of migration as the formation mechanism for massive binaries. I will also present the results of the XUE collaboration, exploring the impact of external UV radiation on the disk structure, warm disk chemistry, and dust mineralogy, all of which are important for planet formation models and exoplanet atmosphere composition.

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The Herschel surveys have enabled the detection of numerous dusty luminous sub-millimetre galaxies in the early universe. Follow-up observations of these sources are essential to determine their nature and the physical properties of their interstellar medium\; reliable measurements of their redshifts are therefore crucial to explore the molecular and atomic gas of these objects. We will here present the results of a Large Program (z-GAL), using NOEMA, aimed at a comprehensive 3 and 2-mm spectroscopic redshift survey of a large (~135 sources) sample of the brightest (S_{500 ?m}>\;80 mJy) galaxies selected from the Herschel H-ATLAS and HerMES surveys, which probe the peak of cosmic evolution (2<\;z<\;4). The results highlight the nature of the sources, including lenses, hyper-luminous galaxies, and proto-clusters. We will describe the main results of the survey, report on recently obtained complementary data, using NOEMA, ALMA and the VLA, addressing aspects of feedback activity in selected sources, and present a serendipitous discovery of a remarkable gravitationally amplified galaxy.

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Star clusters are the one of the most useful places in the universe for studies of stellar and galactic evolution. Formed when stars collapse from the same molecular cloud into a cluster, star clusters offer a unique way to study stars of a homogeneous age and chemical composition across a range of masses. In the age of the Gaia satellite, the census of star clusters in our galaxy has exploded in size - but not without also presenting a number of challenges that require new machine-learning based techniques to solve. In this talk, I will present my work so far aiming to improve many aspects of the census of galactic star clusters in the age of Gaia. After an introduction to the field, I will start by discussing our published catalogue of over 7000 clusters, which represents the largest homogeneous unduplicated catalogue of Milky Way star clusters to date. I will discuss our recently published update to the original catalogue that measures the largest ever sample of cluster masses to better define them observationally, including many surprising results like that most clusters in the galaxy appear to have the same initial mass function - but only after first correcting for selection effects. I will discuss our ongoing work on the sample’s completeness and variable star content. Finally, I will discuss future avenues for research, including upcoming data releases like Gaia DR4 and the LSST.

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KoCo Signature Speaker

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Giant low surface brightness galaxies (gLSBGs) have the largest discs in the Universe with the radii up to 130 kpc. The formation of such enormous discs is a stress-test for the hierarchical galaxy formation paradigm and without clarifying it we cannot paint a coherent picture of galaxy evolution. In the talk I will give the answers to the following questions. How rare are gLSBGs? What are the formation scenarios of gLSBGs? And how does it all correspond to the results of modern cosmological simulations? These answers are based on both in-depth study of 8 gLSBGs, including the results of our deep spectroscopic and photometric observations, HI data collected in the framework of our observing programs and complemented by archival datasets. Finally, we used deep optical images from HSC Subaru Strategic Program and publicly available redshift catalogs, estimated the volume density of gLSBGs in the local Universe and compared it to state-of- the-art numerical simulations.

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