Formation of Disks of Galaxies and Polar-ring Galaxies

星系可分为两大类：椭圆星系和盘星系。后一种类型的星系是由组成恒星的旋转运动支持的，而前一种类型是由它们的随机运动支持的。盖氏盘由中央隆起和旋转薄盘组成。极环星系是一种特殊的星系，它具有一个旋转盘，其旋转轴与主盘的旋转轴正交，而第二个盘被认为是由伙伴星系碰撞产生的下落气体形成的。在早期宇宙盘状星系形成过程中，这些奇特的星系可能是研究盘状星系形成过程的一个很好的目标。由于天气条件恶劣，没有科学的结果。然而，我们获得了明亮的Sa（r！）星系NGC 7742，它有一个明亮突出的核环。通过使用HST档案数据，我们发现该星系的盘在其表面光度学上仅显示出几个百分比的圆对称性偏差。由于盘的Lindblad共振，可形成核环，并有少量的椭圆形不对称。

Galaxies have been classified into two basic categories, elliptical Galaxies and disk galaxies. The latter type of galaxies are supported by rotational motion of constituent stars, while the former type by their random motion. The disk Galaxies consist of a cental bulge and a rotational thin disk. However, no clear understanding is given for their formation mechanisms and which system was firstly formed from proto galaxy clouds.Polar ring galaxies are identified as peculiar galaxies with a rotating disk with rotation axis prthogonal to that of the main disk, where the second disk are believed to be form from infalling gas from colliding partner galaxies. These peculiar galaxies may be a nice targets to study formation process of disks during formation process of disk galaxies in the early universe.We have tried to observe several polar ring galaxies at Okayama Astrophysical Observatory. Due to poor wheather condition, no scientific results have been obtained. However, we obtained nice spectra of a bright Sa (r! ) galaxy NGC 7742, which has a bright prominent nuclear ring. By using HST archival data on this galaxy, we found the disk of the galaxy shows only a few percent deviation from circular symmetry on its surface photometry. Nuclear ring could be formed due to Lindblad resonance of the disk with a small amound of oval asymmmetry.