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The onset of warps in Spitzer observations of edge-on spiral galaxies

Saha, Kanak and de Jong, Roelof and Holwerda, Benne (2009) The onset of warps in Spitzer observations of edge-on spiral galaxies. In: Monthly Notices of the Royal Astronomical Society, 396 (1). pp. 409-422.

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We analyse warps in the nearby edge-on spiral galaxies observed in the Spitzer/Infrared Array Camera (IRAC)4.5-mu m band. In our sample of 24 galaxies, we find evidence of warp in 14 galaxies. We estimate the observed onset radii for the warps in a subsample of 10 galaxies. The dark matter distribution in each of these galaxies are calculated using the mass distribution derived from the observed light distribution and the observed rotation curves. The theoretical predictions of the onset radii for the warps are then derived by applying a self-consistent linear response theory to the obtained mass models for six galaxies with rotation curves in the literature. By comparing the observed onset radii to the theoretical ones, we find that discs with constant thickness can not explain the observations; moderately flaring discs are needed. The required flaring is consistent with the observations. Our analysis shows that the onset of warp is not symmetric in our sample of galaxies. We define a new quantity called the onset-asymmetry index and study its dependence on galaxy properties. The onset asymmetries in warps tend to be larger in galaxies with smaller dis scalelengths. We also define and quantify the global asymmetry in the stellar light distribution, that we call the edge-on asymmetry in edge-on galaxies. It is shown that in most cases the onset asymmetry in warp is actually anticorrelated with the measured edge-on asymmetry in our sample of edge-on galaxies and this could plausibly indicate that the surrounding dark matter distribution is asymmetric.

Item Type: Journal Article
Publication: Monthly Notices of the Royal Astronomical Society
Publisher: Wiley Interscience
Additional Information: Copyright of this article belongs to Wiley Interscience.
Keywords: galaxies:kinematics and dynamics;galaxies:spiral;galaxies: structure
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 14 Dec 2009 06:11
Last Modified: 19 Sep 2010 05:36
URI: http://eprints.iisc.ac.in/id/eprint/21110

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