EFFECTIVE Q CRITERION FOR DISK STABILITY IN AN EXTERNAL POTENTIAL

Jog, Chanda J (2014) EFFECTIVE Q CRITERION FOR DISK STABILITY IN AN EXTERNAL POTENTIAL. In: ASTRONOMICAL JOURNAL, 147 (6).

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Abstract

standard Q criterion (with Q > 1) describes the stability against local, axisymmetric perturbations in a disk supported by rotation and random motion. Most astrophysical disks, however, are under the influence of an external gravitational potential, which can significantly affect their stability. A typical example is a galactic disk embedded in a dark matter halo. Here, we do a linear perturbation analysis for a disk in an external potential and obtain a generalized dispersion relation and the effective stability criterion. An external potential, such as that due to the dark matter halo concentric with the disk, contributes to the unperturbed rotational field and significantly increases its stability. We obtain the values for the effective Q parameter for the Milky Way and for a low surface brightness galaxy, UGC 7321. We find that in each case the stellar disk by itself is barely stable and it is the dark matter halo that stabilizes the disk against local, axisymmetric gravitational instabilities. Thus, the dark matter halo is necessary to ensure local disk stability. This result has been largely missed so far because in practice the Q parameter for a galactic disk is obtained using the observed rotational field that already includes the effect of the halo.

Item Type:	Journal Article
Publication:	ASTRONOMICAL JOURNAL
Publisher:	IOP PUBLISHING LTD
Additional Information:	Copyright for this article belongs to the IOP PUBLISHING LTD, TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND
Keywords:	galaxies: individual (Milky Way, UGC 7321); galaxies: kinematics and dynamics; galaxies: structure; hydrodynamics
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	24 Jun 2014 05:18
Last Modified:	24 Jun 2014 11:52
URI:	http://eprints.iisc.ac.in/id/eprint/49292

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