Promotionskolloquium
Yaoting Yan	SCHEDULED

MPIfR

My thesis investigates the influence of stellar objects onto the interstellar medium (ISM), following two lines of research, determining isotope ratios over much of the Milky Way and observing interstellar ammonia masers. Isotope abundance ratios provide a powerful tool to probe stellar nucleosynthesis, to evaluate the composition of stellar ejecta and to constrain the chemical evolution of the Milky Way. Molecular maser lines are signposts of star formation, probing the excitation and kinematics of very compact regions in the close environment of young stellar objects and providing useful targets for trigonometric parallax measurements. In the first part of this talk, I will present our observations of the J = 2-1 and 3-2 rotational transitions of various rare isotopologic variants of carbon monosulfide (CS), namely C33S, C34S, C36S, 13CS, 13C33S, and 13C34S, toward a large sample of 110 high-mass star-forming regions (HMSFRs) with the IRAM 30-meter telescope. With accurate distances obtained from trigonometric parallaxes, we confirm the previously identified 12C/13C and 32S/34S gradients as a function of Galactocentric distance. There is no 34S/33S gradient, but ratios are well below the values commonly reported in earlier publications. For the first time, we report positive gradients of 32S/33S, 34S/36S, 33S/36S and 32S/36S in our Galaxy. The Galactic 12C/13C gradients derived based on measurements of CN, C18O, and H2CO are in agreement with our results from C34S and indicate that chemical fractionation has little effect on 12C/13C ratios. The measured 34S/33S ratios as a function of Galactocentric radius indicate that 33S has a nucleosynthesis origin similar to that 34S. Interstellar 34S/33S values near the solar neighborhood suggest that the solar system ratio is, as perhaps also the 18O/17O ratio, peculiar. Our measurements support that 36S is a purely secondary nucleus; however, we note that data for lines containing this isotope are still sparse, particularly in the inner Galaxy. The predicted 12C/13C ratios from the latest Galactic chemical evolution (GCE) models are in good agreement with our results, while our 32S/34S and 32S/36S ratios show larger differences at larger Galactocentric distances. 32S/33S ratios show an offset across the entire inner 12 kpc of the Milky Way. All of this can serve as a guideline for further refinements of GCE models. The rest parts of this talk I will focus on ammonia (NH3) masers in our Galaxy. With the Effelsberg 100-m telescope, we discovered widespread non-metastable NH3 maser emission toward 17 high mass star forming regions (HMSFRs) in the Milky Way. This doubles the number of known non-metastable ammonia masers in our Galaxy. These maser lines arise from energy levels between 342 K up and 1449 K above the ground state and this probe the hot dense immediate neighborhoods of newly formed stars. With our higher angular resolution interferometric measurements from the Karl G. Jansky Very Large Array (JVLA), we determined detailed locations for maser spots emitted in multiple non-stable transitions toward a variety of regions. We greatly increase the number of detections in the Galaxy in all the lines targeted. The detected maser spots are not resolved by our JVLA observations. Lower limits to the brightness temperature are >400 K and reach values up to several 10^5 K, manifesting the lines' maser nature. In view of the masers' velocity differences with respect to adjacent hot molecular cores and/or ultra-compact (UC) H II regions, it is argued that all the measured ammonia maser lines may be associated with shocks caused either by outflows or by the expansion of UCH II regions.

	Special Colloquium
Ainara Saiz Perez	SCHEDULED

University of Wuerzburg

The accretion of matter and the formation of relativistic jets in the vicinity of supermassive black holes are closely associated with the acceleration of particles to non-thermal distributions, but the mechanisms behind the coupling of relevant physical processes are not yet fully understood. M87*, the only source for which the black hole horizon scales and jet emission have been spatially resolved, may provide us with an insight into these physical mechanisms. We specifically aim to understand the role and importance of non-thermal particles in the structures observed by mm-VLBI techniques. For this purpose, we carried out general relativistic magnetohydrodynamic (GRMHD) simulations of a jet launching scenario, modelled after M87*. We followed up with radiative transfer calculations, accounting for the synchrotron emission of particles in a hybrid distribution, thermal in the accretion disk and non-thermal in the jet. The non-thermal particles are injected in regions subject to magnetic reconnection, following distributions modelled after particle-in-cell simulations. We find that non-thermal particles may play a crucial role in understanding the images of black hole environments on event horizon scales.

	Special Colloquium
Dr. Elena Shablovinskaya	SCHEDULED

Instituto de Estudios Astrofísicos, Universidad Diego Portales, Chile

Mm emission has been observed as an excess in the SED of RQ AGN. Observations with ALMA have confirmed that mm emission originates from the central, very compact nuclear region (≤ 1 pc) and remains unresolved even at 0.1". While the origin of this emission is still debated, the observed mm spectra and the tight correlation between X-ray and mm emissions suggest that it is a self-absorbed synchrotron emission coming from the accretion disk X-ray corona. Although this mechanism is the most preferable, the absence of correlated variability between high-resolution ALMA mm observations (100 GHz) and X-ray bands (2–10 keV), as recently found in observations of IC 4329A, a nearby unobscured RQ AGN, raises the question about the origin of compact mm emission again. In this talk, I will present the latest results of the investigation of compact mm emission in RQ AGN, including the surprisingly high mm variability, which exceeds that in X-rays. I will also discuss the possible mechanisms for variability in the compact, corona-size region where the mm emission originates, as well as the very first attempts to define the mm origin using ALMA mm polarimetry.

	Main Colloquium
Prof. Dr. Leon Koopmans	SCHEDULED

Groningen University

Observations of the first luminous cosmic structures, with ground and space-based optical and infrared telescopes, are slowly lifting the veil on the complex physical processes that governed the Epoch of Reionization and Cosmic Dawn. These observations, most recently with JWST reaching redshift well into the Cosmic Dawn, however, are only the tip of the iceberg: islands in a sea of neutral hydrogen. I will review the current status of the LOFAR Epoch of Reionization Key-Science Program, presenting our latest improved power-spectrum limits on the 21-cm signal of neutral hydrogen, the constraints it sets on the high-redshift IGM, and present several breakthroughs in our understanding of the data itself, which will be crucial for the future SKA. I will also show the latest results from the NenuFAR Cosmic Dawn Key-Science Program, which aims to measure the 21-cm signal during the Cosmic Dawn. I will place these results in context of SKA and our plans to push towards 21-cm cosmology of the Dark Ages using space-based receivers, such as ALO, currently a pre-phase-A concept for a radio telescope to be placed on the lunar farside by ESA's Argonaut landers.