Observations and chemical modeling of the isotopologues of formaldehyde and the cations of formyl and protonated formaldehyde in the hot molecular core G331.512-0.103

Abstract

In the interstellar cold gas, the chemistry of formaldehyde (H${}_2$CO) can be essential to explain the formation of complex organic molecules. On this matter, the massive and energetic protostellar object G331 is still unexplored and, hence, we carried out a comprehensive study of the isotopologues of H${}_2$CO and formyl cation (HCO${}^{+}$), and of protonated formaldehyde (H${}_2$COH${}^{+}$) through the APEX observations in the spectral window $\sim$159-356~GHz. We employed observational and theoretical methods to derive the physical properties of the molecular gas combining LTE and non-LTE analyses. Formaldehyde was characterized via 35 lines of H${}_2$CO, H${}_2^{13}$CO, HDCO and H${}_2$C${}^{18}$O. The formyl cation was detected via 8 lines of HCO${}^{+}$, H${}^{13}$CO${}^{+}$, HC${}^{18}$O${}^{+}$ and HC${}^{17}$O${}^{+}$. Deuterium was clearly detected via HDCO, whereas DCO${}^{+}$ remained undetected. H${}_2$COH${}^{+}$ was detected through 3 clean lines. According to the radiative analysis, formaldehyde appears to be embedded in a bulk gas with a wide range of temperatures ($T\sim$20-90 K), while HCO${}^{+}$ and H${}_2$COH${}^{+}$ are primarily associated with a colder gas ($T\lesssim$ 30 K). The reaction H${}_2$CO+HCO${}^{+}\to$ H${}_2$COH${}^{+}$ + CO is crucial for the balance of the three species. We used Nautilus gas-grain code to predict the evolution of their molecular abundances relative to H${}_2$ which values at time scales $\sim$10${}^3$ yr matched with the observations in G331: [H${}_2$CO] = (0.2-2) $\times$10${}^{-8}$, [HCO${}^{+}$] = (0.5-4) $\times$10${}^{-9}$ and [H${}_2$COH${}^{+}$] = (0.2-2) $\times$10${}^{-10}$. Based on the molecular evolution of H${}_2$CO, HCO${}^{+}$ and H${}_2$COH${}^{+}$, we hypothesized about the young lifetime of G331, which is consistent with the active gas-grain chemistry of massive protostellar objects.

24 pages, 8 figures, 8 tables. Accepted for publication in The Astrophysical Journal

References in corpus (23)

• The 2014 KIDA network for interstellar chemistry
• Modeling Complex Organic Molecules in dense regions: Eley-Rideal and complex induced reaction
• ExoMol line lists VIII: A variationally computed line list for hot formaldehyde
• SEPIA - a new single pixel receiver at the APEX Telescope
• Grain Surface Reactions in Molecular Clouds: The Effect of Cosmic Rays and Quantum Tunneling
• An ALMA Survey of H${}_2$CO in Protoplanetary Disks
• A systematic TMRT observational study of Galactic ${}^{12}$C/${}^{13}$C ratios from Formaldehyde
• A new look at sulphur chemistry in hot cores and corinos
• Decrease of the organic deuteration during the evolution of Sun-like protostars: the case of SVS13-A
• APECS - The Atacama Pathfinder Experiment Control System
• C18O, 13CO, and 12CO abundances and excitation temperatures in the Orion B molecular cloud: An analysis of the precision achievable when modeling spectral line within the Local Thermodynamic Equilibrium approximation
• Tunneling Rate Constants for H2CO+H on Amorphous Solid Water Surfaces
• Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde IV. The ALMA view of N113 and N159W in the LMC
• Impact of nonconvergence and various approximations of the partition function on the molecular column densities in the interstellar medium
• The connection between warm carbon chain chemistry and interstellar irradiation of star-forming cores
• Isocyanic acid (HNCO) in the Hot Molecular Core G331.512-0.103: Observations and Chemical Modelling
• Chemical composition in the IRAS 16562--3959 high-mass star-forming region
• Diffusive hydrogenation reactions of CO embedded in amorphous solid water at elevated temperatures ~70 K
• Glycolaldehyde formation mediated by interstellar amorphous ice: a computational study
• ALMA Observations of the massive molecular outflow G331.512-0.103 II: physical properties, kinematics, and geometry modeling
• Vacuum ultraviolet photodesorption and photofragmentation of formaldehyde-containing ices
• Chemical evolution of N2H+ in six massive star-forming regions
• A spectral survey of CH3CCH in the Hot Molecular Core G331.512-0.103

Cited by in corpus (1)

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