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Measurement of non-axisymmetry in centres of advanced mergers of galaxies

Jog, Chanda J and Maybhate, Aparna (2006) Measurement of non-axisymmetry in centres of advanced mergers of galaxies. In: Monthly Notices Of The Royal Astronomical Society, 370 (2). pp. 891-901.

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We measure the non-axisymmetry in the luminosity distribution in the inner few kpc of the remnants of advanced mergers of galaxies with a view to understand the relaxation in the central regions. For this, we analyse the images from the Two-Micron All-Sky Survey (2MASS) archival data for a selected sample of 12 merging galaxies, which show signs of interaction but have a single nucleus. The central regions are fitted by elliptical isophotes whose centres are allowed to vary to get the best fit. The centres of isophotes show a striking sloshing pattern with a spatial variation of up to 20-30 per cent within the central 1 kpc. This indicates mass asymmetry and a dynamically unrelaxed behaviour in the central region. Next, we Fourier-analyse the galaxy images while keeping the centre constant and measure the deviation from axisymmetry in terms of the fractional Fourier amplitudes (A(1), A(2), etc.) as a function of radius. All the mergers show a high value of lopsidedness (up to A(1) similar to 0.2) in the central 5 kpc. The m = 2 asymmetry is even stronger, with values of A(2) up to similar to 0.3, and in three cases these are shown to represent bars. The corresponding values denoting non-axisymmetry in inner regions of a control sample of eight non-merger galaxies are found to be several times smaller. Surprisingly, this central asymmetry is seen even in mergers where the outer regions have relaxed into a smooth elliptical-like r(1/4) profile or a spiral-like exponential profile. Thus, the central asymmetry is long lived, estimated to be similar to 1 Gyr, and hence lasts for over 100 local dynamical time-scales. These central asymmetries are expected to play a key role in the future dynamical evolution of the central region of a merger, and can help in feeding of a central active galactic nucleus.

Item Type: Journal Article
Publication: Monthly Notices Of The Royal Astronomical Society
Publisher: RAS
Additional Information: Copyright of this article belongs to RAS.
Keywords: galaxies:evolution – galaxies:kinematics and dynamics – galaxies:interactions– galaxies:photometry – galaxies: structure.
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 31 Mar 2009 11:27
Last Modified: 19 Sep 2010 04:59
URI: http://eprints.iisc.ac.in/id/eprint/18066

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