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Effect of dark matter halo on global spiral modes in galaxies

Ghosh, Soumavo and Saini, Tarun Deep and Jog, Chanda J (2016) Effect of dark matter halo on global spiral modes in galaxies. In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 456 (1). pp. 943-950.

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Official URL: http://dx.doi.org/10.1093/mnras/stv2652

Abstract

Low surface brightness (LSB) galaxies form a major class of galaxies, and are characterized by low disc surface density and low star formation rate. These are known to be dominated by dark matter halo from the innermost regions. Here, we study the role of the dark matter halo on the grand-design, m = 2, spiral modes in a galactic disc by carrying out a global mode analysis in the WKB approximation. The Bohr-Sommerfeld quantization rule is used to determine how many discrete global spiral modes are permitted. First, a typical superthin, LSB galaxy UGC 7321 is studied by taking only the galactic disc, modelled as a fluid; and then the disc embedded in a dark matter halo. We find that both cases permit the existence of global spiral modes. This is in contrast to earlier results where the inclusion of dark matter halo was shown to nearly fully suppress local, swing-amplified spiral features. Although technically global modes are permitted in the fluid model as shown here, we argue that due to lack of tidal interactions, these are not triggered in LSB galaxies. For comparison, we carried out a similar analysis for the Galaxy, for which the dark matter halo does not dominate in the inner regions. We show that here too the dark matter halo has little effect, hence the disc embedded in a halo is also able to support global modes. The derived pattern speed of the global mode agrees fairly well with the observed value for the Galaxy.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the 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
Depositing User: Id for Latest eprints
Date Deposited: 10 Feb 2016 06:06
Last Modified: 10 Feb 2016 06:06
URI: http://eprints.iisc.ac.in/id/eprint/53219

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