The truncation of stellar discs: The magnetic hypothesis

¹ Departamento de Física Teórica y del Cosmos, Universidad de Granada, Spain e-mail: estrella@ugr.es
² Kapteyn Institute, Landleven 12, 9747 AD Groningen, The Netherlands e-mail: jjimenez@astro.rug.nl

Corresponding author: E. Battaner, battaner@ugr.es

Received: 10 January 2002
Accepted: 19 March 2002

Abstract

We propose a hypothesis of the truncation of stellar discs based on the magnetic model of the rotation curve of spiral galaxies. Once the disc had formed and acquired its present structure, approximately, three balanced forces were acting on the initial gas: gravity and magnetic forces, inwards, and centrifugal force. When stars are formed from this gas, the magnetic force is suddenly suppressed. Gravitation alone cannot retain the newly-formed stars and at birth places beyond a certain galactocentric radius they escape to intergalactic space. This radius is the so-called “truncation radius”, which is predicted to be at about 4–5 disc radial scale lengths, in promising agreement with observations.