English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The standard Q criterion (with Q > 1) describes the local stability of a discsupported by rotation and random motion. Most astrophysical discs, however, areunder the influence of an external gravitational field which can affect theirstability. A typical example is a galactic disc embedded in a dark matter halo.Here we do a linear perturbation analysis for a disc in an external field, andobtain a generalized dispersion relation and a modified stability criterion. Anexternal field has two effects on the disc dynamics: first, it contributes tothe unperturbed rotational field, and second, it adds a tidal field term in thestability parameter. A typical disruptive tidal field results in a highermodified Q value and hence leads to a more stable disc. We apply these resultsto the Milky Way, and to a low surface brightness galaxy UGC 7321. We find thatin each case the stellar disc by itself is barely stable and it is the darkmatter halo that stabilizes the disc against local, axisymmetric gravitationalinstabilities. This result has been largely missed so far because in practicethe value for Q for a galactic disc is obtained in a hybrid fashion using theobserved rotational field that is set by both the disc and the halo, and henceis higher than for a pure disc.

Q criterion for disc stability modified by external tidal field