Neutral versus Ion Line Widths in Barnard 5: Evidence for Penetration by Magnetohydrodynamic Waves

Dense cores are the final place where turbulence is dissipated. It has been proposed from theoretical arguments that non-thermal velocity dispersion should be narrower both for molecular ions (compared to neutrals) and transitions with higher critical densities. To test these hypotheses, we compare of N$_2$H$^+$ (1--0) (n$_{\rm crit}$ = $6\times10^4$ cm$^{-3}) NH$_3$ crit}=2\times10^3$ cm$^{-3}), in dense core Barnard 5. We analyse well resolved high signal-to-noise observations (1,1) (2,2) obtained combining GBT VLA data, Argus, which present a similar morphology. % Surprisingly, ion systematically than neutral by 20\%. The derived sonic Mach number, $\mathcal{M}_s \sigma_{\rm NT}/c_s$, peak values $\mathcal{M}_{s, {\rm N_2H^+}} 0.59$ NH}_3} 0.48$ NH$_3$, respectively. This observed difference may indicate magnetic field even deep within still oscillating, as it turbulent region outside core. more strongly dynamically coupled this oscillating neutrals, thus accounting their broader linewidth. If corroborated further observations, finding would shed additional light on transition quiescence cores.