Magnetically Regulated Gas Accretion in High-Redshift Galactic Disks

TL;DR

This paper explores how magnetic fields influence gas accretion in high-redshift galactic disks, potentially causing clumpy star formation by supporting infalling gas until a threshold mass triggers rapid star formation.

Contribution

It introduces a model where magnetic tension regulates gas accretion and star formation, highlighting the importance of magnetic fields in galaxy evolution at high redshift.

Findings

Magnetic pressure can support infalling gas, leading to clumpy star formation.

Threshold mass for gas collapse aligns with observations from galaxy surveys.

Magnetic effects are crucial for realistic simulations of galaxy accretion.

Abstract

Disk galaxies are in hydrostatic equilibrium along their vertical axis. The pressure allowing for this configuration consists of thermal, turbulent, magnetic and cosmic ray components. For the Milky Way(MW) the thermal pressure contributes ~10% of the total pressure near the plane, with this fraction dropping towards higher altitudes. Out of the rest, magnetic fields contribute ~1/3 of the pressure to distances of ~3kpc above the disk plane. In this letter we attempt to extrapolate these local values to high redshift, rapidly accreting, rapidly star forming disk galaxies and study the effect of the extra pressure sources on the accretion of gas onto the galaxies. In particular, magnetic field tension may convert a smooth cold-flow accretion to clumpy, irregular star formation regions and rates. The infalling gas accumulates on the edge of the magnetic fields, supported by magnetic tension. When the mass of the infalling gas exceeds some threshold mass, its gravitational force cannot be balanced by magnetic tension anymore, and it falls toward the disk's plane, rapidly making stars. Simplified estimations of this threshold mass are consistent with clumpy star formation observed in SINS, UDF, GOODS and GEMS surveys. We discuss the shortcomings of pure hydrodynamic codes in simulating the accretion of cold flows into galaxies, and emphasize the need for magneto-hydrodynamic simulations