旋涡星系随倾角的分布(英文)

DISTRIBUTION OF SPIRAL GALAXIES ON VIEWING ANGLES

研究了RC3星系表中旋涡星系随倾角的分布。结果表明 :在 0°～ 80°之间 ,Sa ,Sab ,Scd和Sd星系随倾角的实际分布与Monte -Carlo随机分布在 3σ内吻合较好 ;对Sb和Sbc星系几乎吻合 ;但对Sc星系却相差甚远。由以上的结果分析可知 :在RC3星系表中 ,一些较侧向的旋涡星系 ,等光视短轴的值受核球的影响较大 ;同时 ,Sc星系的实际分布与Monte -Carlo随机分布相差甚远的一个原因可能是由于Hubble分类本身引起的 ,因为Hubble分类是在星系图像上进行 ,而旋臂的缠卷松紧程度却受倾角的影响。这样 ,一些较侧向的Sc星系就会被错分类到早型星系中。结果还直接表明 :如果星系分类只是在图像上进行 ,则各类星系的光度函数就会出现偏差。

This paper presents the normalized inclination distributions for the spiral galaxies in RC3. The results show that, except for the bin of 81°～90° , in which the apparent minor isophotal diameters that are used to obtain the inclinations, are affected by the central bulges, the distributions for Sa, Sab, Scd and Sd are well consistent with those from the Monte-Carlo simulation of random inclinations within 3σ, and Sb and Sbc almost, but Sc is different. One reason that the difference between the real distribution and the Monte-Carlo simulation distribution for Sc may be that, some quite inclined spirals, the arms of which are inherently loosely wound on the galactic plane and should be classified to Sc galaxies, have been incorrectly classified to the earlier ones, because the tightness of spiral arms, which is one of the criteria of the Hubble classification in RC3, is different between on the galactic plane and on the tangent plane of the celestial sphere. Our result also implies that there might exist biases in the luminosity functions of individual Hubble types if spiral galaxies are only classified visually.