Magnetic Fields and Galactic Star Formation Rates

TL;DR

This study investigates how magnetic fields influence star formation in giant molecular clouds within a galaxy, revealing that magnetic strength can significantly suppress star formation, though internal feedback also plays a key role.

Contribution

The paper presents high-resolution simulations showing the impact of magnetic fields on GMC fragmentation and star formation rates, highlighting effects of different magnetic strengths.

Findings

Magnetic fields can significantly suppress star formation in GMCs.

Strong magnetic fields alter cloud fragmentation and dense clump formation.

Internal feedback mechanisms are also crucial in regulating star formation.

Abstract

The regulation of galactic-scale star formation rates (SFRs) is a basic problem for theories of galaxy formation and evolution: which processes are responsible for making observed star formation rates so inefficient compared to maximal rates of gas content divided by dynamical timescale? Here we study the effect of magnetic fields of different strengths on the evolution of giant molecular clouds (GMCs) within a kiloparsec patch of a disk galaxy and resolving scales down to $\simeq0.5\:{\rm{pc}}$. Including an empirically motivated prescription for star formation from dense gas ($n_{\rm{H}}>10^5\:{\rm{cm}^{-3}}$) at an efficiency of 2\% per local free-fall time, we derive the amount of suppression of star formation by magnetic fields compared to the nonmagnetized case. We find GMC fragmentation, dense clump formation and SFR can be significantly affected by the inclusion of magnetic fields, especially in our strongest investigated $B$-field case of $80\:{\rm{\mu}}$G. However, our chosen kpc-scale region, extracted from a global galaxy simulation, happens to contain a starbursting cloud complex that is only modestly affected by these magnetic fields and likely requires internal star formation feedback to regulate its SFR.