Suppression of gravitational instabilities by dominant dark matter halo in low-surface-brightness galaxies

Ghosh, Soumavo and Jog, Chanda J (2014) Suppression of gravitational instabilities by dominant dark matter halo in low-surface-brightness galaxies. In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 439 (1). pp. 929-935.

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Abstract

The low-surface-brightness galaxies are gas rich and yet have a low star formation rate; this is a well-known puzzle. The spiral features in these galaxies are weak and difficult to trace, although this aspect has not been studied much. These galaxies are known to be dominated by the dark matter halo from the innermost regions. Here, we do a stability analysis for the galactic disc of UGC 7321, a low-surface-brightness, superthin galaxy, for which the various observational input parameters are available. We show that the disc is stable against local, linear axisymmetric and non-axisymmetric perturbations. The Toomre Q parameter values are found to be large (>> 1) mainly due to the low disc surface density, and the high rotation velocity resulting due to the dominant dark matter halo, which could explain the observed low star formation rate. For the stars-alone case, the disc shows finite swing amplification but the addition of dark matter halo suppresses that amplification almost completely. Even the inclusion of the low-dispersion gas which constitutes a high disc mass fraction does not help in causing swing amplification. This can explain why these galaxies do not show strong spiral features. Thus, the dynamical effect of a halo that is dominant from inner regions can naturally explain why star formation and spiral features are largely suppressed in low-surface-brightness galaxies, making these different from the high-surface-brightness galaxies.

Item Type:	Journal Article
Publication:	MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Publisher:	OXFORD UNIV PRESS
Additional Information:	copyright for this article belongs to OXFORD UNIV PRESS, GREAT CLARENDON ST, OXFORD OX2 6DP, ENGLAND
Keywords:	instabilities; galaxies: haloes; galaxies: individual: UGC 7321; galaxies: kinematics and dynamics; galaxies: spiral; galaxies: structure
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	26 May 2014 11:26
Last Modified:	27 May 2014 06:34
URI:	http://eprints.iisc.ac.in/id/eprint/48989

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