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: The Astronomical Journal, 147 (6).

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Abstract

The 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:	The Astronomical Journal
Publisher:	The American Astronomical Society
Additional Information:	Copyright for this article belongs to the American Astronomical Society
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	27 May 2014 07:31
Last Modified:	27 May 2014 07:31
URI:	http://eprints.iisc.ac.in/id/eprint/49155

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