Some Aspects of Rotation and Magnetic Field Morphology in the Infrared Dark Cloud G34.43+00.24

TL;DR

This study models how the rotation of infrared dark cloud G34.43+00.24 can generate and amplify magnetic fields of several hundred micro-Gauss, aligning with observations and revealing a power-law relationship between magnetic field strength and density.

Contribution

The paper demonstrates that cloud rotation can produce the observed magnetic field strengths in IRDCs through numerical modeling, highlighting the role of dynamics in magnetic field amplification.

Findings

Magnetic field strengths of several hundred micro-Gauss are consistent with observations.

Magnetic field strength increases with density approximately as a power-law with an index of 0.45.

Rotational motions can significantly amplify magnetic fields in IRDCs.

Abstract

The infrared dark clouds (IRDCs) are molecular clouds with relatively greater values in their magnetic field strengths. For example, the IRDC G34.43+00.24 (G34) has magnetic field strength of the order of a few hundred micro-Gauss. In this study, we investigate if the dynamic motions of charged particles in an IRDC such as G34 can produce this magnetic field strength inside it. The observations show that the line-of-sight velocity of G34 has global gradient. We assume that the measured global velocity gradient can correspond to the cloud rotation. We attribute a large-scale current density to this rotating cloud by considering a constant value for the incompleteness of charge neutrality and the velocity differences between the positive and negative particles with very low ionization fractions. We use the numerical package FISHPACK to obtain the magnetic field strength and its morphology on the plane-of-sky within G34. The results show that the magnetic field strengths are of the order of several hundred micro-Gauss, and its morphology in the plane-of-sky is somewhat consistent with the observational results. We also obtain the relationship between magnetic field strength and density in G34. The results show that with increasing density, the magnetic field strength increases approximately as a power-law function. The amount of power is approximately equal to 0.45, which is suitable for molecular clouds with strong magnetic fields. Therefore, we can conclude that the dynamical motion of IRDCs, and especially their rotations, can amplify the magnetic field strengths within them.