Magnetically Regulated Gas Accretion in High-Redshift Galactic Disks

Details Magnetically Regulated Gas Accretion in High-Redshift Galactic Disks Magnetically Regulated Gas Accretion in High-Redshift Galactic Disks

2009-08-12

arxiv.org/abs/0908.1786v1

Astrophysical Journal Letters 702 (2009) L101-L104

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

12 pages, 3 figures, accepted to ApJL

Scientific paper

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

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