PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar

(Abridged) We investigate the impact of radiative feedback from massive stars on their natal cloud and focus on the transition from the HII region to the atomic PDR (crossing the ionisation front (IF)), and the subsequent transition to the molecular PDR (crossing the dissociation front (DF)). We use high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science Program. The NIRSpec data reveal a forest of lines including, but not limited to, HeI, HI, and CI recombination lines, ionic lines, OI and NI fluorescence lines, Aromatic Infrared Bands (AIBs including aromatic CH, aliphatic CH, and their CD counterparts), CO2 ice, pure rotational and ro-vibrational lines from H2, and ro-vibrational lines HD, CO, and CH+, most of them detected for the first time towards a PDR. Their spatial distribution resolves the H and He ionisation structure in the Huygens region, gives insight into the geometry of the Bar, and confirms the large-scale stratification of PDRs. We observe numerous smaller scale structures whose typical size decreases with distance from Ori C and IR lines from CI, if solely arising from radiative recombination and cascade, reveal very high gas temperatures consistent with the hot irradiated surface of small-scale dense clumps deep inside the PDR. The H2 lines reveal multiple, prominent filaments which exhibit different characteristics. This leaves the impression of a "terraced" transition from the predominantly atomic surface region to the CO-rich molecular zone deeper in. This study showcases the discovery space created by JWST to further our understanding of the impact radiation from young stars has on their natal molecular cloud and proto-planetary disk, which touches on star- and planet formation as well as galaxy evolution.Comment: 52 pages, 30 figures, submitted to A&

Etude de la réactivité de CO2 et d'OCS vis-à-vis de métaux de transition par spectroscopie en matrice à basse température

BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Theoretical description of interstellar ices from a multimethod approach

National audienceEven if the ISM remains a cold environment with only few energy available, dynamics effects cannot be neglected since the surface state may be significantly altered due to thermal energy dissipation. It is possible to carry electronic structure calculations on reduced and distorted structures that may reproduce somehow a thermally relaxed surface. Classical molecular dynamics based on a semi-empirical potential remains a method of choice to account for explicit dynamical effects and for large scale surfaces. Within the classical description of the intermolecular forces, only physisorption is accessible. This limitation can be overcome through the combination of dynamics/force field simulations and Self-consistent charge density functional tight binding (SCC-DFTB) calculations. This will be illustrated in the case of the adsorption of PAHs on crystalline and amorphous ices. We will present a complete description of PAH-ice interaction in the ground electronic state at low temperature, providing the binding energies and barrier heights necessary to the on-going improvement of astrochemical models

Theoretical description of interstellar ices from a multimethod approach

National audienceEven if the ISM remains a cold environment with only few energy available, dynamics effects cannot be neglected since the surface state may be significantly altered due to thermal energy dissipation. It is possible to carry electronic structure calculations on reduced and distorted structures that may reproduce somehow a thermally relaxed surface. Classical molecular dynamics based on a semi-empirical potential remains a method of choice to account for explicit dynamical effects and for large scale surfaces. Within the classical description of the intermolecular forces, only physisorption is accessible. This limitation can be overcome through the combination of dynamics/force field simulations and Self-consistent charge density functional tight binding (SCC-DFTB) calculations. This will be illustrated in the case of the adsorption of PAHs on crystalline and amorphous ices. We will present a complete description of PAH-ice interaction in the ground electronic state at low temperature, providing the binding energies and barrier heights necessary to the on-going improvement of astrochemical models

Infrared matrix- isolation and theoretical studies of interactions between CH3I and water

International audienceGaseous methyl iodine (CH3I) is naturally emitted in the atmosphere over oceans through the algae and phytoplankton activities. The fate of naturally emitted CH3I is of great interest because of the oxidizing properties of iodine and its impact on the catalytic destruction of the ozone layer. Additionally, CH3I is one of the gaseous species that can be produced in the case of severe nuclear accident, so, its radiological impact requires knowledge about its behavior in the atmosphere. Water is one of the major species in the atmosphere, which is responsible for atmospheric aerosol nucleation and cloud condensation nuclei. Water can also act as a reactive medium leading to secondary product formation. The study of the interaction between methyl iodine and water at the molecular scale is contributing for a better understanding of the fate of such halogen alkyl into the atmosphere. Here the micro-hydration of CH3I was investigated using cryogenic matrix experiments which were supported by theoretical DFT calculations. A large excess of water regarding CH3I was used in order to mimic atmospheric conditions. Dimers and trimers of CH3I were observed despite the high water amount in the initial mixture. This may be explained by the low affinity of CH3I with water. Considering the concentration of CH3I used in the experiments, the aggregates are likely formed in the gas phase. The interaction between CH3I and H2O molecules studied for the first time experimentally and supported by DFT calculations highlights that, in the atmosphere, gaseous methyl iodine and water will likely form aggregates of water and CH3I polymers instead of (CH3I)m-(H2O)n hetero complexes. However, mixed CH3I:H2O complexes 1:1, 1:2 and 1:3 (see Figure) have been observed , whereas 2:1 and 2:2 complexes appear as minor species

Infrared matrix- isolation and theoretical studies of interactions between CH3I and water

International audienceGaseous methyl iodine (CH3I) is naturally emitted in the atmosphere over oceans through the algae and phytoplankton activities. The fate of naturally emitted CH3I is of great interest because of the oxidizing properties of iodine and its impact on the catalytic destruction of the ozone layer. Additionally, CH3I is one of the gaseous species that can be produced in the case of severe nuclear accident, so, its radiological impact requires knowledge about its behavior in the atmosphere. Water is one of the major species in the atmosphere, which is responsible for atmospheric aerosol nucleation and cloud condensation nuclei. Water can also act as a reactive medium leading to secondary product formation. The study of the interaction between methyl iodine and water at the molecular scale is contributing for a better understanding of the fate of such halogen alkyl into the atmosphere. Here the micro-hydration of CH3I was investigated using cryogenic matrix experiments which were supported by theoretical DFT calculations. A large excess of water regarding CH3I was used in order to mimic atmospheric conditions. Dimers and trimers of CH3I were observed despite the high water amount in the initial mixture. This may be explained by the low affinity of CH3I with water. Considering the concentration of CH3I used in the experiments, the aggregates are likely formed in the gas phase. The interaction between CH3I and H2O molecules studied for the first time experimentally and supported by DFT calculations highlights that, in the atmosphere, gaseous methyl iodine and water will likely form aggregates of water and CH3I polymers instead of (CH3I)m-(H2O)n hetero complexes. However, mixed CH3I:H2O complexes 1:1, 1:2 and 1:3 (see Figure) have been observed , whereas 2:1 and 2:2 complexes appear as minor species

Infrared matrix- isolation and theoretical studies of interactions between CH3I and water

International audienceGaseous methyl iodine (CH3I) is naturally emitted in the atmosphere over oceans through the algae and phytoplankton activities. The fate of naturally emitted CH3I is of great interest because of the oxidizing properties of iodine and its impact on the catalytic destruction of the ozone layer. Additionally, CH3I is one of the gaseous species that can be produced in the case of severe nuclear accident, so, its radiological impact requires knowledge about its behavior in the atmosphere. Water is one of the major species in the atmosphere, which is responsible for atmospheric aerosol nucleation and cloud condensation nuclei. Water can also act as a reactive medium leading to secondary product formation. The study of the interaction between methyl iodine and water at the molecular scale is contributing for a better understanding of the fate of such halogen alkyl into the atmosphere. Here the micro-hydration of CH3I was investigated using cryogenic matrix experiments which were supported by theoretical DFT calculations. A large excess of water regarding CH3I was used in order to mimic atmospheric conditions. Dimers and trimers of CH3I were observed despite the high water amount in the initial mixture. This may be explained by the low affinity of CH3I with water. Considering the concentration of CH3I used in the experiments, the aggregates are likely formed in the gas phase. The interaction between CH3I and H2O molecules studied for the first time experimentally and supported by DFT calculations highlights that, in the atmosphere, gaseous methyl iodine and water will likely form aggregates of water and CH3I polymers instead of (CH3I)m-(H2O)n hetero complexes. However, mixed CH3I:H2O complexes 1:1, 1:2 and 1:3 (see Figure) have been observed , whereas 2:1 and 2:2 complexes appear as minor species