Structure, Dynamics and Deuterium Fractionation of Massive Pre-Stellar Cores

Abstract

High levels of deuterium fraction in N${}_2$H${}^{+}$ are observed in some pre-stellar cores. Single-zone chemical models find that the timescale required to reach observed values ($D_{\mathrm{frac}}^{{\mathrm{N}}_2{\mathrm{H}}^{+}}\equiv {\mathrm{N}}_2{\mathrm{D}}^{+}/{\mathrm{N}}_2{\mathrm{H}}^{+}\gtrsim 0.1$) is longer than the free-fall time, possibly ten times longer. Here, we explore the deuteration of turbulent, magnetized cores with 3D magnetohydrodynamics simulations. We use an approximate chemical model to follow the growth in abundances of N${}_2$H${}^{+}$ and N${}_2$D${}^{+}$. We then examine the dynamics of the core using each tracer for comparison to observations. We find that the velocity dispersion of the core as traced by N${}_2$D${}^{+}$ appears slightly sub-virial compared to predictions of the Turbulent Core Model of McKee & Tan, except at late times just before the onset of protostar formation. By varying the initial mass surface density, the magnetic energy, the chemical age, and the ortho-to-para ratio of H${}_2$, we also determine the physical and temporal properties required for high deuteration. We find that low initial ortho-to-para ratios ($\lesssim 0.01$) and/or multiple free-fall times ($\gtrsim 3$) of prior chemical evolution are necessary to reach the observed values of deuterium fraction in pre-stellar cores.

arXiv comment20 pages, 18 figures; accepted for publication in ApJ

References in corpus (36)

• The Formation of Massive Stars from Turbulent Cores
• Athena: A New Code for Astrophysical MHD
• Competitive accretion in embedded stellar cluster
• Physical Conditions in Regions of Star Formation
• The Energy Dissipation Rate of Supersonic, Magnetohydrodynamic Turbulence in Molecular Clouds
• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• Molecular ions in L1544. II. The ionization degree
• Radiation-Hydrodynamic Simulations of Collapse and Fragmentation in Massive Protostellar Cores
• Cosmic-ray ionization of molecular clouds
• Molecular Cloud Evolution II. From cloud formation to the early stages of star formation in decaying conditions
• Investigating the Cosmic-Ray Ionization Rate in the Galactic Diffuse Interstellar Medium through Observations of H3+
• Collapse of massive magnetized dense cores using radiation-magneto-hydrodynamics: early fragmentation inhibition
• The Interplay of Magnetic Fields, Fragmentation and Ionization Feedback in High-Mass Star Formation
• Gravitational Collapse in Turbulent Molecular Clouds. II. Magnetohydrodynamical Turbulence
• Collapse, outflows and fragmentation of massive, turbulent and magnetized prestellar barotropic cores
• Chemical modeling of L183 (= L134N) : an estimate of the ortho/para H2 ratio
• Importance of the Initial Conditions for Star Formation - I. Cloud Evolution and Morphology
• Dynamics and Depletion in Thermally Supercritical Starless Cores
• The Fragmentation of Magnetized, Massive Star-Forming Cores with Radiative Feedback
• Mid-Infrared Extinction Mapping of Infrared Dark Clouds II. The Structure of Massive Starless Cores and Clumps
• The Dynamics of Massive Starless Cores with ALMA
• Magnetic fields during the early stages of massive star formation - I. Accretion and disk evolution
• Radiation-Hydrodynamic Simulations of Massive Star Formation with Protostellar Outflows
• Deuteration as an evolutionary tracer in massive-star formation
• Star Cluster Formation in Turbulent, Magnetized Dense Clumps with Radiative and Outflow Feedback
• Radiation Feedback, Fragmentation, and the Environmental Dependence of the Initial Mass Function
• Infall through the evolution of high-mass star-forming clumps
• Magnetic fields during the early stages of massive star formation - II. A generalised outflow criterion
• Mapping Large-Scale CO Depletion in a Filamentary Infrared Dark Cloud
• The Deuterium Fractionation Timescale in Dense Cloud Cores: A Parameter Space Exploration
• An Ordered Bipolar Outflow from a Massive Early-Stage Core
• The Deuterium Fraction in Massive Starless Cores and Dynamical Implications
• A Virialized Filamentary Infrared Dark Cloud
• Widespread deuteration across the IRDC G035.39-00.33
• Accretion and Diffusion Timescales in Sheets and Filaments
• Dynamics, CO depletion, and deuterium fractionation of the dense condensations within the fragmented prestellar core Orion B9-SMM 6

Cited by in corpus (10)

• Identification of prestellar cores in high-mass star forming clumps via ${\mathrm{H}}_2{\mathrm{D}}^{+}$ observations with ALMA
• Zooming in to Massive Star Birth
• 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
• Deuterium fractionation and H2D+ evolution in turbulent and magnetized cloud cores
• Fast deuterium fractionation in magnetized and turbulent filaments
• Chemical post-processing of magneto-hydrodynamical simulations of star-forming regions: robustness and pitfalls
• Deuterium Chemodynamics of Massive Pre-Stellar Cores
• Digging into the Interior of Hot Cores with ALMA (DIHCA). V. Deuterium Fractionation of Methanol
• Fire from Ice - Massive Star Birth from Infrared Dark Clouds