SFB1601 Colloquium

Astronomical observations of molecules are buoyed by laboratory astrophysics investigations of a variety of processes. Observations of the interstellar medium need spectral line positions to find molecules, rates of reaction to explain to feed chemical models, and collisional (de)excitation rates to predict the abundance of molecules under the peculiar conditions of space. Laboratory astrophysics measurements or predictions can provide all this information using a wide variety of techniques. Given the strong link between rotational spectroscopy and astrochemistry through several microwave, millimeter, and sub-millimeter telescopes, the role of rotational spectroscopy can be expanded beyond its traditional role of providing spectral line positions in laboratory measurements. I will discuss new experiments that push rotational spectroscopy into the detection of products of reaction and validation of collisional (de)excitation rates all in support of astrochemistry.
(Cologne, Host: Stephan Schlemmer)

In my talk I will present recent results from state-of-the-art simulations of molecular clouds and star formation. I will focus on the interplay of magnetic fields, turbulence and chemistry and their effect on the structure evolution in clouds and the subsequent star formation process. Specifically, I will show how magnetic field lead to a stabilisation of clouds on larger scales, whereas on smaller scales gravity takes over. I will discuss how this effect is reflected in the chemical composition of the clouds and the structure of magnetic fields. Furthermore, I will present a novel analysis of the 3D morphology of substructures contained in the clouds, which show a intriguing transition from sheet-like structures to filamentary structures, in excellent agreement with recent observations. Lastly, I will connect the results of these simulations to actual observations by discussing synthetic observations created from the simulations. Specifically I will focus on dust polarisation maps and discuss what we can learn from them about the underlying 3D magnetic field structure and how accurately magnetic field properties can be inferred from such observations.

Star formation is ubiquitous in the Galaxy, but the physical and chemical conditions in star-forming sites might differ as a function of galactocentric radius. Due to the negative metallicity gradient, the efficiency of gas cooling and dust shielding decreases in more distant regions. A lower interstellar radiation field and a decrease in cosmic-ray fluxes lead to a decrease in gas heating and ultimately cause lower gas and dust temperatures in the outer Galaxy. The balance between these processes sets the physical conditions of the gas and dust and likely affects star-formation rates and efficiencies. In this talk, we will present the first research highlights of the recently completed APEX legacy survey “Outer Galaxy High Resolution Survey” (OGHReS), which covers 100 deg^2 in the 3rd Galactic quadrant in the 2-1 transition of CO and its rare isotopologues. We will discuss important characteristics of the structure of the outer Galaxy, highlighting the differences with the inner Galaxy. We observed that large-scale filaments in the outer Galaxy are fundamentally quiescent objects, with a mass one order of magnitude lower compared to similar size filaments in the inner Galaxy. Additionally, outer galaxy filaments are found exclusively in inter-arm regions, which might point towards a different formation mechanism with respect to the inner Galaxy. The most prominent filament in the outer Galaxy, Falcor, is the only exception, being a site of efficient star formation and a host of the hot core candidate. Finally, we will present preliminary results of the follow-up studies of selected  star-forming clumps in additional molecular and atomic lines, and discuss their gradients across the Milky Way. We will initiate the discussion to what extent the outer Galaxy can act as a laboratory of star formation in a low-metallicity environment, and propose the next steps necessary to interpret star formation in diverse ecosystems.

High-resolution spectroscopic measurements performed in the laboratory enable the determination of molecular parameters and the identification of molecular species in different environments. The detection of new species and an estimation of its density allow in a second step to constrain astrophysical/chemical models. Very precise laboratory measurements may also challenge our understanding of quantum chemistry and fundamental physics.

Several high-resolution spectrometers were built recently in Louvain-la-Neuve. Those instruments work in different spectral ranges, microwave, near-infrared and UV to measure different molecular systems such as isolated molecules, neutral van der Waals complexes and molecular ions. During this talk, we will introduce a buffer gas cooling cell (20K) which is combined to a cavity ringdown spectrometer working in the near-infrared range. The set-up is illustrated in Figure 1. This instrument has been specifically designed to obtain reference measurements on complex molecules such as CH₃OH probed in the overtone range. Our recent results concerning methanol will be shown and the tools developed to tackle the complex spectral signature will be detailed. Part of the complex spectral signature of methanol is also illustrated in Figure 1. Several potential upgrades of this instrument, for instance combining it with a home-built femtosecond laser to reach higher precision will be presented. Further, I will present action photodissociation spectroscopy measurements and the associated analysis concerning ionic species such as N₂O⁺. To finish, our results concerning the study of molecular aggregation at the molecular scale will be presented. 

Figure 1: The Experimental set-up combining a buffer gas cooling cell and a cavity ringdown spectrometer is presented in the upper panel. Laser light is injected in a high-finesse optical cavity and the lifetime of the photons inside this cavity is measured as a function of the laser frequency. The lower panel presents the spectrum of methanol measured in the 2OH overtone range at a temperature of 25 K. 

(Cologne, Host: Oskar Asvany)

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(Cologne)

Laboratory astrophysics bridges studies of atomic and molecular species in interstellar and circumstellar media and planetary atmospheres conducted through astronomical observations, and studies of these species or their analogues that we can create in the laboratory and probe in situ. Many laboratory experiments are devoted to studies of solid-state or surface reactions that lead to a greater complexity (comparing to the gas phase) of molecular species. Complex organic and prebiotic molecules can be formed through surface reaction pathways linking astrophysics/astrochemistry with the big scientific question – the origin of Life on Earth.In my talk, I will provide a brief introduction to laboratory astrophysics and to cosmic surfaces, will present a new view of cosmic dust grains, and will discuss results of experiments on the catalytic formation of molecules thereon.  

Schematic figure showing dust grains (in grey) mixed with ice molecules (in blue) and the main sources of their processing in astrophysical environments (from Potapov et al., Phys. Rev. Lett., 2020, 124,221103).

(Cologne, Host: Stephan Schlemmer)