Chemical modeling of internal photon-dominated regions surrounding deeply embedded HC/UCHII regions

Abstract

We aim to investigate the chemistry of internal photon-dominated regions surrounding deeply embedded hypercompact and ultracompact HII regions. We search for specific tracers of this evolutionary stage of massive star formation that can be detected with current astronomical facilities. We modeled hot cores with embedded HC/UCHII regions, by coupling the astrochemical code Saptarsy to a radiative transfer framework obtaining the spatio-temporal evolution of abundances as well as time-dependent synthetic spectra. In these models where we focused on the internal PDR surrounding the HI region, the gas temperature is set to the dust temperature and we do not include dynamics thus the density structure is fixed. We compared this to hot molecular core models and studied the effect on the chemistry of the radiation field which is included in the HII region models only during the computation of abundances. In addition, we investigated the chemical evolution of the gas surrounding HII regions with models of different densities at the ionization front, different sizes of the ionized cavity and different initial abundances. We obtain the time evolution of synthetic spectra for a dozen of selected species as well as ratios of their integrated intensities. We find that some molecules such as C, N2H+, CN, and HCO do not trace the inner core and so are not good tracers to distinguish the HII/PDR regions to the HMCs phase. On the contrary, C+ and O trace the internal PDRs, in the two models starting with different initial abundances, but are unfortunately currently unobservable with the current achievable spatial resolution because of the very thin internal PDR (r < 100 AU). In addition, we find that the abundance profiles are highly affected by the choice of the initial abundances, hence the importance to properly define them.

References in corpus (34)

• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• Structure of Stationary Photodissociation Fronts
• A model for atomic and molecular interstellar gas: The Meudon PDR code
• Non-thermal desorption from interstellar dust grains via exothermic surface reactions
• A three-phase chemical model of hot cores: the formation of glycine
• Evolution of Massive Protostars with High Accretion Rates
• Polycylcic Aromatic Hydrocarbons (PAH's) in dense cloud chemistry
• H II regions: Witnesses to massive star formation
• Chemistry in Disks. IV. Benchmarking gas-grain chemical models with surface reactions
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• Evolution of electronic structure of doped Mott insulators - reconstruction of poles and zeros of Green's function
• Surface chemistry in the interstellar medium - I - H2 formation by Langmuir-Hinshelwood and Eley-Rideal mechanisms
• The physical and chemical structure of Sagittarius B2, I. Three-dimensional thermal dust and free-free continuum modeling on 100 au to 45 pc scales
• A Unified Monte Carlo Treatment of Gas-Grain Chemistry for Large Reaction Networks. II. A Multiphase Gas-Surface-Layered Bulk Model
• The interstellar gas-phase chemistry of HCN and HNC
• A new modified-rate approach for gas-grain chemical simulations
• Understanding Spatial and Spectral Morphologies of Ultracompact H II Regions
• Molecule survival in magnetized protostellar disk winds. I. Chemical model and first results
• Modelling Herschel observations of hot molecular gas emission from embedded low-mass protostars
• The HNC/HCN Ratio in Star-Forming Regions
• Abundances and Isotope Ratios in the Magellanic Clouds: The Star Forming Environment of N113
• Multidimensional chemical modelling, II. Irradiated outflow walls
• Different evolutionary stages in massive star formation. Centimeter continuum and H2O maser emission with ATCA
• Submillimeter continuum observations of Sagittarius B2 at subarcsecond spatial resolution
• Dust dynamics and evolution in expanding HII regions. I. Radiative drift of neutral and charged grains
• A New Determination of the Binding Energy of Atomic Oxygen on Dust Grain Surfaces: Experimental Results and Simulations
• Deciphering the ionized gas content in the massive star forming complex G75.78+0.34
• Deuteration around the ultracompact HII region Mon R2
• Reversal of infall in SgrB2(M) revealed by Herschel/HIFI observations of HCN lines at THz frequencies
• From forced collapse to H ii region expansion in Mon R2: Envelope density structure and age determination with Herschel
• Evolution of complex organic molecules in hot molecular cores: Synthetic spectra at (sub-)mm wavebands
• The dynamical influence of cooling in the envelope of prestellar and protostellar cores
• The first CO+ image: Probing the HI/H2 layer around the ultracompact HII region Mon R2
• The warm CO gas along the UV-heated outflow cavity walls: a possible interpretation for the Herschel/PACS CO spectra of embedded YSOs

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