Applying a novel and universal action spectroscopic technique, called leak-out spectroscopy, this paper revisits the $v$₃ proton shuttle motion of the symmetric linear molecule He–H⁺–He. For this, a 4 K cryogenic ion trap apparatus has been combined with a high-resolution quantum cascade laser operating around 1300 cm^_-1. Seven rovibrational lines of this fundamental three-nucleus-four-electron system are recorded, demonstrating the suitability of the leak-out method for such fundamental hydrogen–helium cations. (Cologne)

Much of our understanding of how star formation works in nature comes from the analysis of molecular line observations. A major difficulty in interpreting these observations is the complex relationship between line emission and mass: different lines preferentially trace different physical regimes, depending on the chemistry of the molecule in question. Astrochemical modelling can be used to turn this difficulty into a strength, highlighting specific molecules as tracers of key physical processes, but to date models have often been highly idealised, ignoring the complex evolutionary pathways characteristic of turbulent molecular clouds. I will present results from the NEATH project, which combines state-of-the-art MHD simulations of molecular clouds with a large gas-grain chemical network to track the chemical evolution of important observational species such as HCN and N2H+. Compared to previous astrochemical modelling efforts, two key differences emerge: the simulated cloud masses are dominated by moderate density (~10^3 cm-3) material, so that all common ‘dense gas tracers’, with the notable exception of N2H+, are actually poor tracers of the high-density star-forming component of the clouds; and the highly non-linear evolution of the cloud material inverts many commonly-used chemical age diagnostics, with supposedly ‘late-forming’ molecules appearing well before their ‘early-forming’ counterparts.
(Cologne, Host Daniel Seifried)

(Cologne, Host Arshia Jacob)

(Cologne)

(Cologne)

(Cologne, Host Peter Schilke)

Luminous and ultra-luminous infrared galaxies (U/LIRGs) are powered by intense nuclear starbursts and active galactic nuclei (AGN). Often triggered by mergers, these systems represent galaxies undergoing rapid transformation and may offer a key window into the co-evolution of galaxies and their central supermassive black holes (SMBHs). However, the centres of these galaxies are frequently so deeply embedded in gas and dust that the processes driving this evolution remain largely hidden.

The most extremely obscured systems host Compact Obscured Nuclei (CONs) — among the most deeply embedded and rapidly evolving galactic nuclei known. These objects may harbour heavily buried and rapidly accreting SMBHs, potentially representing a missing link between gas-rich galaxy centres and luminous AGN.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), we have conducted high-resolution studies of deeply embedded nuclei in nearby U/LIRGs, including several CONs. ALMA’s sensitivity and angular resolution provide a unique view of the gas properties and kinematics in these dense environments. Our pc-scale observations of HCN (the CONfirm survey) and H₂O (the ALMA water maser study) trace inflows of low-angular-momentum gas and powerful outflows in galaxy centres, revealing how gas is transported to the nucleus and how feedback operates in these extreme environments.

These observations allow us to chart the evolutionary cycles of some of the most gas-rich galaxy centres known. I will present evidence for a new inflow-powered feedback cycle that may drive SMBH growth in extremely dust-obscured galaxies, as well as a new method for determining the luminosities of deeply buried AGN using millimetre continuum observations. Finally, I will show recent JWST observations of molecular absorption and ices in two nearby CONs, providing new insight into the physical conditions and hidden activity in these remarkable nuclei.
(Cologne, Host Peter Schilke)