The Study of Ring Structures in Galaxies

星系中的環狀結構

吳禹葶

指導教授 ： 江瑛貴

國立清華大學/理學院/物理學系/博士(2013年)

摘要

在本論文中，我們研究經由星系碰撞所產生的軸對稱和非軸對稱環狀星系的形成及演化。經由多體模擬，我們發現環狀星系可能是經由矮星系和盤狀星系的正面碰撞和非正面碰撞所產生。當矮星系及盤狀星系的相對速度較小時，或矮星系的質量較重時，可以形成密度反差(density contrast)較高的環。此外，當矮星系及盤狀星系碰撞的傾斜角(inclination angle)較大時，可以產生離心率較大的環；當兩星系的碰撞參數(impact parameter)較大時，盤狀星系的中心較易偏移。之後，我們研究環的徑向速度及方位速度。我們發現，當矮星系的質量較大時，會導致環的徑向速度較大。當矮星系及盤狀星系碰撞的傾斜角較大時，則會降低環的平均方位速度，並增加徑向速度及方位速度在環上的變化量。此外，當兩星系的碰撞參數較大時，也會增加環上徑向速度的變化量。最後，我們研究氣體在星系NGC 4911 和NGC 4921 的分佈。從兩星系氣體HI 和CO 的分佈，我們猜測這兩個星系可能在星系團中經歷過衝壓力(ram pressure)或是星系之間的交互作用。

關鍵字

環狀星系 ； 星系形成 ； 星系交互作用 ； 多體模擬

並列摘要

In this dissertation, we study the formation and evolution of axis-symmetric and asymmetric ring galaxies through the collision scenario. Head-on and non-axisymmetric collisions between the dwarf galaxy and the disk galaxy were performed through N-body simulations to address their origins. It was found that the simulations with smaller initial relative velocities between two galaxies, or in the cases with heavier dwarf galaxies, could produce rings with higher density contrasts. In addition, it was shown that the collisions with larger inclination angle could produce the elliptical rings with the larger eccentricity. The impact parameter has a significant positive correlation with the location of the disk center. Besides, we study the radial velocity and the azimuthal velocity of rings, and concluded that a positive correlation was found between the radial velocity of the ring and the dwarf’s mass. In addition, when the inclination angle of the galaxy pair is larger, the average azimuthal velocity of the ring is lower, but the variations of the radial velocity and the azimuthal velocity of the ring were larger. A positive correlation was also found between the impact parameter and the range of the radial velocity on the ring. Finally, we study the morphology of the gas within two Hi deficient disk galaxies, NGC 4911 and NGC 4921. From the Hi and CO data, these two galaxies might have experienced the ram pressure or the galactic interactions in the Coma Cluster.

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