星系彎曲(galactic warp)是一種普遍存在於星系中的現象，自四十年前首次發現，
至今仍是一個重要的研究課題。學者們提出各種可能的假說及數值模型，以了解星系彎曲產生的機制。
我們根據Sparke(2002)的觀點，以重力作用為模擬的重點，
並希望進一步仔細分析討論Jiang與Binney(1999)的宇宙暗流(cosmic infall)模型。
因此我們建立了簡單的動力學模型，來模擬不同條件下星系彎曲的形成。
在這些模型中，我們使用不同函數形式與質量的宇宙暗流，並討論內盤(inner disc)質量增加，
對形成星系彎曲的影響。之後則進一步討論另一種亦在星系中相當普遍的
結構–旋臂(spiral arm)–與星系彎曲之間的關聯。我們發現，
內盤質量增加對星系彎曲的形成並無明顯的助益，
但可能是形成高速雲(high velocity clouds)的原因。
而宇宙暗流則與星系彎曲的形成有關，不同的宇宙暗流分佈函數與總質量，
可造成不同振幅的星系彎曲。
至於旋臂與星系彎曲，兩者分別是同一個三維非球對稱結構，在不同二維平面上的投影；
因此它們的形態演化與演化速率，彼此間有密切的關係。

The warping of galactic discs is a general
phenomenon for disc galaxies
and it has been an important subject for four decades since its
first discovery.
Sparke (2002)gives an argument
showing that the warps are a gravitational phenomenon.
We thus follow this line and focus on the gravity here,
and we wish to further explore the parameter spaces
for the model proposed by Jiang & Binney (1999).
We try
different types
of cosmic infall with different total mass and
also study the effect of disc accretion.
Then we study the relation between warps and spiral arms.
We find that the mass accretion along the galactic plane is not
helpful for the formation of warps but could be a good way to produce
halo stars and high velocity clouds.
On the other hand, all three types of cosmic infall we introduce
could produce warps with different amplitudes and shapes at different time.
These results reconfirm that warps is a halo phenomenon and
closely related to the tilted non-axisymmetric
component of halo.
Warps and spiral arms are projections on different two-dimensional plane of the same non-axisymmetric structure in three-dimensional space.

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