A simple model of magnetically induced warps

TL;DR

This paper presents a simple magnetic model to explain galactic warps, deriving a formula that matches observed warp curves and suggests magnetic fields influence galaxy morphology.

Contribution

It introduces a straightforward formula for warp curves based on magnetic hypotheses, linking magnetic field properties to observable galaxy warps.

Findings

The model reproduces the warp curve of NGC 5907.

Fitting warp curves can estimate magnetic field strength and direction.

The proposed magnetic field distribution is consistent with boundary conditions.

Abstract

Assuming the magnetic hypothesis for the formation of warps, we deduce a very simple formula for the warp curve in an idealized scenario. According to this formula the warp rises as the third power of radius in the innermost warped region, reaches the maximum slope at intermediate radii and has an asymptotic slope coincident with the direction of the extragalactic magnetic field. In most cases, however, the galaxy's limited size prevents the observation of the full curve. Even though the model is highly simplified, it basically reproduces real warp curves, in particular the 21 cm warp curve of NGC 5907. If the magnetic model were considered to be correct, the fitting of warp curves could allow rough estimations of the strength and direction of the magnetic field. We also propose a magnetic field distribution for the outermost part of the galaxy, matching the boundary conditions of being azimuthal inside, and constant at infinity. We use this magnetic field distribution to show that the assumptions made to obtain the warp curve with our simple model cannot introduce important errors.