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Rotational action spectroscopy is an experimental method in which rotational spectra of molecules, typically in the microwave to sub-mm-wave domain of the electromagnetic spectrum (B1–1000 GHz), are recorded by action spectroscopy. Action spectroscopy means that the spectrum is recorded not by detecting the absorption of light by the molecules, but by the action of the light on the molecules, e.g., photon-induced dissociation of a chemical bond, a photon-triggered reaction, or photodetachment of an electron. Typically, such experiments are performed on molecular ions, which can be well controlled and mass-selected by guiding and storage techniques. Though coming with many advantages, the application of action schemes to rotational spectroscopy was hampered for a long time by the small energy content of a corresponding photon. Therefore, the first rotational action spectroscopic methods emerged only about one decade ago. Today, there exists a toolbox full of different rotational action spectroscopic schemes which are summarized in this review.

DOI: 10.1039/d1cp03975j

We showed that the fraction of [CII] - HII Region related emission varies a lot for any given line-of-sight, and it can be as high as 70% of the total observed[CII] emission. Those results were then used to predict the [N/H] elemental abundance in the GC (a value poorly constraint  in the GC). Our results showed that it should be much larger ~x7.5 than what is measured in the Galactic Disk, and nearly x2.3 larger than previous measurements int he Arched Filaments. 

Radiative and mechanical feedback of massive stars regulates star formation and galaxy evolution. Positive feedback triggers the creation of new stars by collecting dense shells of gas, while negative feedback disrupts star formation by shredding molecular clouds. Although key to understanding star formation, their relative importance is unknown. Here, we report velocity-resolved observations from the SOFIA (Stratospheric Observatory for Infrared Astronomy) legacy program FEEDBACK of the massive star-forming region RCW 120 in the [CII] 1.9-THz fine-structure line, revealing a gas shell expanding at 15 km/s. Complementary APEX (Atacama Pathfinder Experiment) CO J = 3-2 345-GHz observations exhibit a ring structure of molecular gas, fragmented into clumps that are actively forming stars. Our observations demonstrate that triggered star formation can occur on much shorter time scales than hitherto thought (<0.15 million years), suggesting that positive feedback operates on short time periods.

Science Advances

Uni Köln

Molecular ions have long been considered key intermediates in the evolution of molecular complexity in the interstellar medium. However, owing to their reactivity and transient nature, ions have historically proved challenging to study in terrestrial laboratory experiments. In turn, their detection and characterization in space is often contingent upon advances in the laboratory spectroscopic techniques used to measure their spectra. In this Review, we discuss the advances over the past 50 years in laboratory methodologies for producing molecular ions and probing their rotational, vibrational and electronic spectra. We largely focus this discussion around the widespread H₃⁺ cation and the ionic products originating from its reaction with carbon atoms. Finally, we discuss the current frontiers in this research and the technical advances required to address the spectroscopic challenges that they represent.

Nature Reviews Physics

We present numerical simulations of molecular clouds formation including the chemical evolution of H2 and CO. We discuss the spatial resolution required to obtain numerically converged chemical abundances.

https://doi.org/10.1093/mnras/stz052

We present dust polarisation radiative transfer simulations obtained with POLARIS of simulations of magnetised molecular clouds. We discuss the accuracy of actual polarisation observations and the origin of depolarisation in molecular clouds.

https://doi.org/10.1093/mnras/sty2831

We present molecular cloud simulations including radiative stellar feedback. We discuss the reduction of the star formation efficiency and the dispersal of molecular clouds due to stellar feedback.

https://doi.org/10.1093/mnras/sty2938

To date, infrared interferometry at best achieved contrast ratios of a few times 10−4 on bright targets. GRAVITY, with its dual-field mode, is now capable of high contrast observations, enabling the direct observation of exoplanets. We demonstrate the technique on HR 8799, a young planetary system composed of four known giant exoplanets.

https://doi.org/10.1051/0004-6361/201935253

We measure for the first time the overall extent within which stars in distant galaxies were born. At all cosmic epochs, star formation in massive galaxies preferentially takes place in their central region, indicating that we are witnessing the final assembly of their stellar bulges. Few galaxies have a more compact star-forming extent, and all of them produce stars at a much higher rate than the average. This suggests a different mechanism triggering their star formation activities, such as the merger of two gas-rich disks.

https://doi.org/10.1051/0004-6361/201935178

The IRAM/GISMO 2 millimeter survey in the COSMOS field provides a unique view on star formation at the time when the Universe was only two billion years old. It reveals a significant population of extreme galaxies. Compared to the Milky-Way, they are about three times more massive, and form about 1000 times more stars per year. The sheer existence of these galaxies, soon after the Big-Bang, challenges current galaxy formation models.

https://iopscience.iop.org/article/10.3847/1538-4357/ab1912