Found 22 talks width keyword galactic structure

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Wednesday July 16, 2008
Dr. Gyula Jozsa
Netherlands Institute for Radio Astronomy, the Netherlands

Abstract

Warps of disk galaxies are ubiquitous. In almost every disk galaxy a bending of the disk occurs where the stars fade away and hence where the dark matter halo becomes dominant. A clear understanding of this phenomenon has not been reached yet. Analysing H I observations of a small sample of symmetric, warped disk galaxies we found that they exhibit a two-disk structure, the warp being the transition from the inner flat disk to an outer, inclined one. At the transition radius, the rotation curve changes. This points towards symmetric warps being a long-lived phenomenon reflecting an internal change in the structure of the Dark Matter halo.
While warps usually occur where the stellar disks fade, examples of extreme warps are known that commence already at the centre of galaxies. One is present in the neutral gas disk of the "Spindle Galaxy "NGC 2685, formerly thought of as being a two-ringed polar ring galaxy. Utilising deep HI observations, we found that the two-ringed appearance is due to projection effects and that it rather possesses one coherent,extremely warped HI disk. Our success in fitting a tilted-ring model to the HI component, and, with that, assuming circular orbits of the tracer material, and the shape of the fitted rotation curve hint towards a rather spherical shape of the overall potential.

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Thursday June 19, 2008
Prof. Ronald Buta
University of Alabama, USA

Abstract

Bars are important engines for the evolution of structure in galaxies. Bars can cause secular evolution of both the gas and stellar distributions in galaxies, and recently it has been suggested that bars may be recurrent features, forming, dissolving, and reforming over a Hubble time. Models also have suggested that the strength of bars depends on how effectively the bar can transfer angular momentum to outer halo material. Evaluating current models requires an effective way of quantifying the strengths of bars. In my presentation, I will describe recent attempts to use gravitational torques implied by near-infrared images as a means of quantifying both bars and spirals in disk galaxies. I will also describe some of the recent findings based on Fourier analysis of early-type galaxy bars.

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