Galactic disc warps due to intergalactic accretion flows onto the disc

TL;DR

This paper proposes that intergalactic medium accretion onto galactic discs, through angular momentum transfer, can generate observed warps, aligning with galactic chemical evolution and observed azimuthal dependencies.

Contribution

It introduces a plausible mechanism where intergalactic accretion causes galactic warps via angular momentum transfer, supported by quantitative predictions matching observations.

Findings

Intergalactic accretion can produce warps consistent with observations.

The predicted infall rate aligns with chemical evolution models.

Azimuthal dependence of disc scaleheight supports the mechanism.

Abstract

The accretion of the intergalactic medium onto the gaseous disc is used to explain the generation of galactic warps. A cup-shaped distortion is expected, due to the transmission of the linear momentum; but, this effect is small for most incident inflow angles and the predominant effect turns out to be the transmission of angular momentum, i.e. a torque giving an integral-sign shaped warp. The torque produced by a flow of velocity ~100 km/s and baryon density ~10^{-25} kg/m^3, which is within the possible values for the intergalactic medium, is enough to generate the observed warps and this mechanism offers quite a plausible explanation. The inferred rate of infall of matter, ~1 M_sun/yr, to the Galactic disc that this theory predicts agrees with the quantitative predictions of chemical evolution resolving key issues, notably the G-dwarf problem. Sanchez-Salcedo (2006) suggests that this mechanism is not plausible because it would produce a dependence of the scaleheight of the disc with the Galactocentric azimuth in the outer disc, but rather than being an objection this is another argument in favour of the mechanism because this dependence is actually observed in our Galaxy.