Parsec-scale cosmic-ray ionisation rate in Orion

Abstract

Cosmic rays regulate the dynamics and the chemical processes in the densest and coldest regions of the ISM. Still, the determination of the cosmic-ray ionisation rate of H${}_2$ (${\zeta }_{{\mathrm{H}}_2}^{\mathrm{ion}}$) is plagued by uncertainties in the adopted chemical networks and the analysis techniques. This work aims to homogeneously estimate the ${\zeta }_{{\mathrm{H}}_2}^{\mathrm{ion}}$ at parsec scales towards the Orion Molecular Clouds OMC-2 and OMC-3, probing its variation across a whole star-forming region and a range of column densities never explored before. The most recent ${\zeta }_{{\mathrm{H}}_2}^{\mathrm{ion}}$ estimates are based on o$-$H${}_2$D${}^{+}$, whose abundance we proxy through CO depletion taking advantage of the existing correlation between the two parameters. We therefore employ observations of C${}^{18}$O (2$-$1), HCO${}^{+}$ (1$-$0) and DCO${}^{+}$ (3$-$2) towards OMC-2 and OMC-3 to determine the depletion factor, the deuteration fraction and, ultimately, a map of ${\zeta }_{{\mathrm{H}}_2}^{\mathrm{ion}}$ in these two regions. The depletion factors and deuteration fractions correlate with the total column density of H${}_2$, the N${}_2$H${}^{+}$ emission and the coldest fields across OMC-2 and OMC-3. The cosmic-ray ionisation rate shows values of ${\zeta }_{{\mathrm{H}}_2}^{\mathrm{ion}}\sim 5\times 10^{-18}-10^{-16}$~s${}^{-1}$, in agreement with previous o$-$H${}_2$D${}^{+}$-based estimates. In addition, it shows an overall decrease for increasing $N({\mathrm{H}}_2$), consistently with the predictions from theoretical models. Our approach provides results comparable with theoretical predictions and previous independent studies, confirming the robustness of the analytical framework and the viability of CO depletion as proxy for o$-$H${}_2$D${}^{+}$. By exploring the major limitations of the method, we suggest interferometric observations as mandatory to reliably constrain the ${\zeta }_{{\mathrm{H}}_2}^{\mathrm{ion}}$ also at parsec scales.

References in corpus (69)

• The SIMBAD astronomical database
• A computer program for fast non-LTE analysis of interstellar line spectra
• Cold Dark Clouds: The Initial Conditions for Star Formation
• The distance to the Orion Nebula
• A KInetic Database for Astrochemistry (KIDA)
• Systematic Molecular Differentiation in Starless Cores
• Our astrochemical heritage
• Probing the evolutionary status of starless cores through N2H+ and N2D+ observations
• Cosmic-ray ionization of molecular clouds
• Investigating the Cosmic-Ray Ionization Rate in the Galactic Diffuse Interstellar Medium through Observations of H3+
• High-resolution wide-band Fast Fourier Transform spectrometers
• Complete Depletion in prestellar cores
• An ALMA study of the Orion Integral Filament: I. Evidence for narrow fibers in a massive cloud
• Abundant H2D+ in the pre-stellar core L1544
• Chemistry in Infrared Dark Cloud Clumps: a Molecular Line Survey at 3 mm
• Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion
• Survey of ortho-H2D+(1_{1,0}-1_{1,1}) in dense cloud cores
• The cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions
• The Green Bank Ammonia Survey (GAS): First Results of NH3 mapping the Gould Belt
• Chemical evolution in the early phases of massive star formation. I
• The JCMT BISTRO Survey: The magnetic field strength in the Orion A filament
• Protostars: Forges of cosmic rays?
• Disruption of the Orion Molecular Core 1 by the stellar wind of the massive star ${\theta }^1$ Ori C
• Impact of low-energy cosmic rays on star formation
• Gravitational collapse of the OMC-1 region
• HCN/HNC intensity ratio: a new chemical thermometer for the molecular ISM
• Astrochemistry of Sub-Millimeter Sources in Orion: Studying the Variations of Molecular Tracers with Changing Physical Conditions
• New extended deuterium fractionation model: assessment at dense ISM conditions and sensitivity analysis
• Mapping Large-Scale CO Depletion in a Filamentary Infrared Dark Cloud
• Benchmarking spin-state chemistry in starless core models
• Searching for massive pre--stellar cores through observations of N2H+ and N2D+
• SOLIS II. Carbon-chain growth in the Solar-type protocluster OMC2-FIR4
• Cosmic-ray acceleration in young protostars
• Galactocentric variation of the gas-to-dust ratio and its relation with metallicity
• The Central 300 pc of the Galaxy probed by infrared spectra of H${}_3^{+}$ and CO: part I. Predominance of warm and diffuse gas and high H${}_2$ ionization rate
• The Ionization Fraction in Dense Molecular Gas II: Massive Cores
• Cosmic rays in molecular clouds probed by H${}_2$ rovibrational lines -- Perspectives for the James Webb Space Telescope
• Resolved Depletion Zones and Spatial Differentiation of N2H+ and N2D+
• Chemical evolution in the early phases of massive star formation II: Deuteration
• SOLIS IV. Hydrocarbons in the OMC-2 FIR 4 region, a probe of energetic particle irradiation of the region
• Characterizing the line emission from molecular clouds. Stratified random sampling of the Perseus cloud
• Deuterium fractionation and the degree of ionisation in massive clumps within infrared dark clouds
• High angular resolution observations towards OMC-2 FIR 4: Dissecting an intermediate-mass protocluster
• The cosmic-ray ionisation rate in the pre-stellar core L1544
• The core population and kinematics of a massive clump at early stages: an ALMA view
• Survey of ortho-H${}_2$D${}^{+}$ in high-mass star-forming regions
• Non-thermal emission from cosmic rays accelerated in HII regions
• Identification of prestellar cores in high-mass star forming clumps via ${\mathrm{H}}_2{\mathrm{D}}^{+}$ observations with ALMA
• A new proxy to estimate the cosmic-ray ionisation rate in dense cores
• First ALMA maps of cosmic ray ionisation rate in high-mass star-forming regions
• Chemical modeling of Infrared Dark Clouds: the Role of Surface Chemistry
• Nobeyama 45-m Mapping Observations toward Orion A.I. Molecular Outflows
• On the size of the CO-depletion radius in the IRDC G351.77-0.51
• The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). VI. The core-scale CO-depletion
• The chemical structure of young high-mass star-forming clumps: (II) parsec-scale CO depletion and deuterium fraction of $\mathrm{HC}{\mathrm{O}}^{+}$
• The 3D structure of CO depletion in high-mass prestellar regions
• Characterizing the line emission from molecular clouds. II. A comparative study of California, Perseus, and Orion A
• A timeline for massive star-forming regions via combined observation of o-H${}_2$D${}^{+}$ and N${}_2$D${}^{+}$
• Expanding CO Shells in the Orion A Molecular Cloud
• X-ray embedded stars as driving sources of outflow-driven turbulence in OMC1-S
• Fast deuterium fractionation in magnetized and turbulent filaments
• Abundance ratios of OH/CO and HCO+/CO as probes of the cosmic ray ionization rate in diffuse clouds
• Infall/Expansion Velocities in the Low-Mass Dense Cores L492, L694-2, and L1521F: Dependence on Position and Molecular Tracer
• OMC-2 FIR 4 under the microscope: Shocks, filaments, and a highly collimated jet at 100 au scales
• Emergence of high-mass stars in complex fiber networks (EMERGE). I. Early ALMA Survey: observations and massive data reduction
• APEX observations of ortho-H${}_2$D${}^{+}$ towards dense cores in the Orion B9 filament
• Variations of the HCO${}^{+}$, HCN, HNC, N${}_2$H${}^{+}$ and NH${}_3$ deuterium fractionation in high-mass star-forming regions
• Magnetic field structure of OMC-3 in the far infrared revealed by SOFIA/HAWC+
• The ionization fraction in OMC-2 and OMC-3

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• The impact of attenuation on cosmic-ray chemistry: I. Abundances and chemical calibrators in molecular clouds
• Carbon chain diversity in L1544 and IRAS 16293-2422: an astrochemical pathfinder study for the SKAO
• Chemistry of Dark Molecular Clouds
• CO Depletion in Infrared Dark Clouds
• Deuterium fractionation and CO depletion in Barnard 5