Lopsided spiral galaxies

Jog, Chanda J and Combes, Francoise (2009) Lopsided spiral galaxies. In: Physics Reports, 471 (2). pp. 75-111.

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Abstract

The light distribution in the disks of many galaxies is ‘lopsided’ with a spatial extent much larger along one half of a galaxy than the other, as seen in M101. Recent observations show that the stellar disk in a typical spiral galaxy is significantly lopsided, indicating asymmetry in the disk mass distribution. The mean amplitude of lopsidedness is 0.1, measured as the Fourier amplitude of the m=1 component normalized to the average value. Thus, lopsidedness is common, and hence it is important to understand its origin and dynamics. This is a new and exciting area in galactic structure and dynamics, in contrast to the topic of bars and two-armed spirals (m=2) which has been extensively studied in the literature. Lopsidedness is ubiquitous and occurs in a variety of settings and tracers. It is seen in both stars and gas, in the outer disk and the central region, in the field and the group galaxies. The lopsided amplitude is higher by a factor of two for galaxies in a group. The lopsidedness has a strong impact on the dynamics of the galaxy, its evolution, the star formation in it, and on the growth of the central black hole and on the nuclear fuelling. We present here an overview of the observations that measure the lopsided distribution, as well as the theoretical progress made so far to understand its origin and properties. The physical mechanisms studied for its origin include tidal encounters, gas accretion and a global gravitational instability. The related open, challenging problems in this emerging area are discussed.

Item Type:	Journal Article
Publication:	Physics Reports
Publisher:	Elsevier Science
Additional Information:	Copyright of this article belongs to Elsevier Science.
Keywords:	Galaxies:Kinematics and dynamics; Galaxies:ISM;Galaxies: Spiral;Galaxies:Structure;Galaxies:Individual:M101.
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	28 Aug 2009 15:46
Last Modified:	19 Sep 2010 05:30
URI:	http://eprints.iisc.ac.in/id/eprint/19873

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