• C5: HYACINTH – A New Model for Molecular Hydrogen and Carbon Chemistry in Cosmological Simulations (Prachi Khatri)

    C5: HYACINTH – A New Model for Molecular Hydrogen and Carbon Chemistry in Cosmological Simulations (Prachi Khatri)

    Modelling the molecular gas content of galaxies is a highly non-linear, multi-scale problem in astrophysics. On one hand, it is necessary to simulate galaxies in realistic environments as they are affected by outflows and gas accretion from the cosmic web. On the other hand, molecular-cloud chemistry is regulated by conditions on sub-parsec scales.

    To overcome this challenge, we have developed a new sub-grid model, HYACINTH – HYdrogen And Carbon chemistry in the INTerstellar medium in Hydro simulations – that can be embedded into cosmological simulations of galaxy formation to calculate the non-equilibrium abundances of molecular hydrogen and its carbon-based tracers, namely, CO, C, and C+ on the fly. Our model captures the effects of the ‘microscopic’ (i.e., unresolved) density structure on the ‘macroscopic’ (i.e., resolved) chemical abundances in cosmological simulations using a variable probability distribution function of sub-grid densities within each resolution element. 

    The chemical abundances from HYACINTH are in good agreement with observations of nearby and high-redshift galaxies. We are now running a suite of cosmological galaxy formation simulations with HYACINTH that will allow us to address fundamental questions regarding the contribution of different galaxies to the global H2 budget and the reliability of different molecular gas tracers across ISM conditions and galaxy environments at high redshifts (z ≳ 3).

    The paper describing the model has been accepted for publication in A&A. 
    DOI: 10.1051/0004-6361/202449640

    Figure caption: Column density maps of different species in a pre-simulated galaxy (from Tomassetti et al. 2015) post-processed with HYACINTH. The first two panels show the distribution of total and molecular hydrogen from the simulation, while the other panels show the species obtained in post-processing. CO is concentrated in regions with the highest N(H2), while C and C+ are more widespread; C+ even extends out to regions lacking a significant amount of H2and closely mirrors the total gas distribution.

  • A4: First Measurements of the rotational Spectrum of Phosphabutyne (Sven Thorwirth, Luis Bonah) 

    A4: First Measurements of the rotational Spectrum of Phosphabutyne (Sven Thorwirth, Luis Bonah) 

    Many places in space are too far away to learn about them by sending spacecraft there. So they cannot be examined directly but instead, we can learn about them by analyzing their emitted light.
    Due to quantum mechanics, each molecule has a set of characteristic transition lines that uniquely identify it. When these transition lines are found in the emitted spectrum, we can be sure that the respective molecule appears in the observed object.
    However, to identify molecules in space, we first have to understand their characteristic patterns in the laboratory. We do so by measuring the rotational spectrum of the molecules in our experiment and then fitting quantum mechanical models to them. These models can then be used by astronomers to identify the molecules in space and also to infer the physical conditions of the corresponding regions in space. For example, the temperature can be deduced from intensity relations, the pressure from the lineshape, and the molecule’s abundance can be inferred from its intensity.
    Here, we measured the pure rotational spectrum of phosphabutyne (C2H5CP) for the first time and analyzed its vibrational ground state as well as its three singly 13C-substituted isotopologues. This will allow astronomers to search for phosphabutyne in space and determine the prevailing conditions of the corresponding regions. The figure shows a section of the measured broadband spectrum on top, highlighting the pattern repeating with the total angular momentum quantum number J, while the zoom-in on the bottom highlights the very good agreement between the calculated and measured spectrum, especially when applying a small shift of 126 MHz.
    This work was performed in collaboration with Jean-Claude Guillemin (University Rennes) and Michael E. Harding (KIT).

  • A6/B2: First detection of ionized carbon in a high latitude cloud raises new questions (Nicola Schneider, Volker Ossenkopf-Okada)

    A6/B2: First detection of ionized carbon in a high latitude cloud raises new questions (Nicola Schneider, Volker Ossenkopf-Okada)

    What is the structure and chemical composition of gas that may feed future star formation? Before interstellar gas turns dense enough to form new stars it is not fully molecular yet but in some so far unknown transitional state. A special case of such gas clouds are given by high-latitude clouds representing material that may fall onto the plane of the Milky Way.
    In a recently accepted paper by Nicola Schneider and collaborators we reported results from SOFIA/upGREAT observations of a number of diffuse and high latitude clouds in the Milky Way, in particular the Draco, Spider, Polaris and Musca clouds. In only one of them, the Draco cloud, we detected emission of ionized carbon in spite of it being neither the densest cloud nor the one irradiated the strongest by known sources.
    When trying to model the emission of all observations in terms of an astrochemical model of a photon-dominated region it turns out, that the model is not able to simultaneously explain the strength of the continuum emission from dust and the ionized carbon line. The ionized carbon detection and also the non-detections suggest a very low impinging UV field well below what is actually observed taking all the known stars in the environment. For the Draco cloud we can explain the difference by the additional energy from a shock that is produced when the cloud is hitting the interstellar gas of the Milky Way and some shielding of the cloud by interstellar dust in atomic gas. However, for the other clouds, we do not have a consistent explanation yet.
    The paper combined the results from a fruitful collaboration between the CRC 1601 subprojects B2 and A6.

    Figure caption: Schematic illustration of the illumination of a high-latitude cloud by UV radiation from stars in the plane of the Milky Way. The orange cylinder along the path between star and cloud indicates the dust column which attenuates the UV-field.