Neutral vs Ion Linewidths in Barnard 5: Evidence for Penetration by MHD Waves

Abstract

Dense cores are the final place where turbulence is dissipated. It has been proposed from theoretical arguments that the non-thermal velocity dispersion should be narrower both for molecular ions (compared to neutrals) and for transitions with higher critical densities. To test these hypotheses, we compare the velocity dispersion of N${}_2$H${}^{+}$ (1--0) (n${}_{\mathrm{crit}}$ = $6\times 10^4$ cm${}^{-3})andNH$_3$(n$_{\rm crit}=2\times10^3$cm$^{-3}), in the dense core Barnard 5. We analyse well resolved and high signal-to-noise observations of NH${}_3$ (1,1) and (2,2) obtained with combining GBT and VLA data, and N${}_2$H${}^{+}$ (1--0) obtained with GBT Argus, which present a similar morphology. % Surprisingly, the non-thermal velocity dispersion of the ion is systematically higher than that of the neutral by 20\%. The derived sonic Mach number, ${\mathcal{M}}_s={\sigma }_{\mathrm{NT}}/c_s$, has peak values ${\mathcal{M}}_{s,{\mathrm{N}}_2{\mathrm{H}}^{+}}=0.59$ and ${\mathcal{M}}_{s,{\mathrm{NH}}_3}=0.48$ for N${}_2$H${}^{+}$ and NH${}_3$, respectively. % This observed difference may indicate that the magnetic field even deep within the dense core is still oscillating, as it is in the turbulent region outside the core. The ions should be more strongly dynamically coupled to this oscillating field than the neutrals, thus accounting for their broader linewidth. If corroborated by further observations, this finding would shed additional light on the transition to quiescence in dense cores.

arXiv commentAccepted for publication in ApJ. 14 pages, 11 Figures

References in corpus (39)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Astropy: A Community Python Package for Astronomy
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• MAMBO Mapping of Spitzer c2d Small Clouds and Cores
• Dense Cores in Dark Clouds. XIV. N2H+(1-0) maps of dense cloud cores
• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• The Universality of Turbulence in Galactic Molecular Clouds
• Molecular ions in L1544. II. The ionization degree
• Observing the gas temperature drop in the high-density nucleus of L 1544
• SCUBA Polarization Measurements of the Magnetic Field Strengths in the L183, L1544, and L43 Prestellar Cores
• An ALMA study of the Orion Integral Filament: I. Evidence for narrow fibers in a massive cloud
• Direct observation of a sharp transition to coherence in Dense Cores
• The COMPLETE Survey of Outflows in Perseus
• Helical Fields and Filamentary Molecular Clouds II - Axisymmetric Stability and Fragmentation
• The Green Bank Ammonia Survey (GAS): First Results of NH3 mapping the Gould Belt
• On the frequency of N2H+ and N2D+
• Mapping Distances Across the Perseus Molecular Cloud Using CO Observations, Stellar Photometry, and Gaia DR2 Parallax Measurements
• Interstellar Turbulence: II. Energy Spectra of Molecular Regions in the Outer Galaxy
• Dense core formation in supersonic turbulent converging flows
• Probing the Turbulence Dissipation Range and Magnetic Field Strengths in Molecular Clouds
• ALMACAL IV: A catalogue of ALMA calibrator continuum observations
• EVLA Observations of the Barnard 5 Star-Forming Core: Embedded Filaments Revealed
• Droplets I: Pressure-Dominated Sub-0.1 pc Coherent Structures in L1688 and B18
• Probing the Magnetic Field with Molecular Ion Spectra
• Dense gas kinematics and a narrow filament in the Orion A OMC1 region using NH3
• The JCMT BISTRO Survey: The Magnetic Field In The Starless Core $\rho$ Ophiuchus C
• Alfvenic Turbulence Beyond the Ambipolar Diffusion Scale
• ALMA photometry of extragalactic radio sources
• A spider-like outflow in Barnard 5 - IRS 1: The transition from a collimated jet to a wide-angle outflow?
• Dissecting the super-critical filaments embedded in the 0.5 pc subsonic region of Barnard 5
• Multicomponent kinematics in a massive filamentary IRDC
• Ubiquitous $\mathrm{N}{\mathrm{H}}_3$ supersonic component in L1688 coherent cores
• Contraction Signatures Toward Dense Cores in the Perseus Molecular Cloud
• Probing the Turbulence Dissipation Range and Magnetic Field Strengths in Molecular Clouds. II. Directly Probing the Ion-neutral Decoupling Scale
• Observational Diagnostics for Two-Fluid Turbulence in Molecular Clouds As Suggested by Simulations
• Magnetic Field Structure of Dense Cores using Spectroscopic Methods
• Kinematics in Partially Ionised Molecular Clouds: Implications for the Transition to Coherence
• Reflection and dissipation of Alfvén waves in interstellar clouds
• Calibration of Argus and the 4mm Receiver on the GBT

Cited by in corpus (12)

• The Central 1000 au of a Pre-stellar Core Revealed with ALMA. II. Almost Complete Freeze-out
• An Interferometric View of H-MM1. I. Direct Observation of NH3 Depletion
• Probing the physics of star formation (ProPStar): I. First resolved maps of the electron fraction and cosmic-ray ionization rate in NGC 1333
• Flow of gas detected from beyond the filaments to protostellar scales in Barnard 5
• Transport of Protostellar Cosmic Rays in Turbulent Dense Cores
• Can we observe the ion-neutral drift velocity in prestellar cores?
• Three-dimensional magnetic fields of molecular clouds
• On the propagation of Alfvén waves in the dusty interstellar medium. Can we neglect dust inertia in molecular clouds?
• Probing the Physics of Star-Formation (ProPStar) III. No evidence for dissipation of turbulence down to 20 mpc (4 000 au) scale
• Deuterium fractionation in cold dense cores in the low-mass star forming region L1688
• Thermal damping of Weak Magnetosonic Turbulence in the Interstellar Medium
• Deuterium fractionation and CO depletion in Barnard 5