Magnetic fields in star forming environments: how does field strength affect gas on spiral arm and cloud scales?

TL;DR

This study uses MHD simulations to explore how magnetic field strength influences star formation, cloud structure, and magnetic alignment on galactic and cloud scales, revealing that stronger fields suppress star formation and alter cloud orientations.

Contribution

It provides new insights into the impact of magnetic field strength on star formation efficiency, cloud alignment, and the magnetic criticality in galactic environments through detailed MHD modeling.

Findings

Magnetic fields suppress star formation by up to 50%.

Cloud alignment shifts from parallel to perpendicular with increasing field strength.

Magnetic criticality varies with measurement direction, affecting interpretation.

Abstract

We investigate star formation from subparsec to kpc scales with magnetohydrodynamic (MHD) models of a cloud structure and a section of galactic spiral arm. We aim to understand how magnetic fields affect star formation, cloud formation and how feedback couples with magnetic fields on scales of clouds and clumps. We find that magnetic fields overall suppress star formation by $\sim$10% with a weak field (5 $\mu$G), and $\sim50$% with a stronger field (50 $\mu$G). Cluster masses are reduced by about 40% with a strong field but show little change with a weak field. We find that clouds tend to be aligned parallel to the field with a weak field, and become perpendicularly aligned with a stronger field, whereas on clump scales the alignment is more random. The magnetic fields and densities of clouds and clumps in our models agree with the Zeeman measurements of the Crutcher relation $B-\rho$ in the weaker field models, whilst the strongest field models show a relation which is too flat compared to the observations. In all our models, we find both subcritical and supercritical clouds and clumps are present. We also find that if using a line of sight (1D) measure of the magnetic field to determine the critical parameter, the magnetic field, and thereby also criticality, can vary by a factor of 3-4 depending on whether the direction the field is measured along corresponds to the direction of the ordered component of the magnetic field.