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arXiv 0708.2631astro-ph
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由Sloan数字巡天观测得到的早型星系的内禀轴比分布

Intrinsic Axis Ratio Distribution of Early-type Galaxies From Sloan Digital Sky Survey

Taysun Kimm, Sukyoung K. Yi

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9 pages, 11 figures, Accepted for publication in ApJ
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摘要：

利用Sloan数字巡天数据Release 5研究了早型星系的内禀轴比分布。我们在$0.05 \leq z \leq 0.06$建立了一个3,922个目视检查的早期类型星系的体积有限的样本，仔细考虑由星系等照度线的大小和光度引起的采样偏差。我们试图去项目所观察到的ARD成三维类型（扁圆，扁长，和三轴），这是在三轴性方面进行分类。我们证实，没有线性组合的$randomly$分布轴比的三种类型可以重现所观察到的ARD。然而，使用高斯本征分布，我们发现了与扁圆、长轴和三轴（两个轴比中的三轴）的优选平均轴比的数据的合理拟合，其中扁圆、长轴和三轴类型的分数为\textrm{O:P:T} =0.29^{ \pm 0.09}：0.26^{ \pm 0.11}：0.45^{ \pm 0.13} $. We have also found that the luminous sample ($-23.3 < M_r \leq-21.2 $) tends to have more triaxials than the less luminous ($-21.2 < M_r <-19.3 $）样品确实。扁圆星系在亮度较低的星系中相对较多。有趣的是，两个光度类别中三轴类型的轴比的偏好非常相似。我们没有发现任何显着的影响，本地星系数密度的ARD。我们发现，结果可能会受到严重影响的数据选择和类型分类方案的细节。警告和星系形成的影响进行了讨论。

英文摘要：

Using Sloan Digital Sky Survey Data Release 5, we have investigated the intrinsic axis ratio distribution (ARD) for early-type galaxies. We have constructed a volume-limited sample of 3,922 visually-inspected early-type galaxies at $0.05 \leq z \leq 0.06$ carefully considering sampling biases caused by the galaxy isophotal size and luminosity. We attempt to de-project the observed ARD into three-dimensional types (oblate, prolate, and triaxial), which are classified in terms of triaxiality. We confirm that no linear combination of $randomly$-distributed axis ratios of the three types can reproduce the observed ARD. However, using Gaussian intrinsic distributions, we have found reasonable fits to the data with preferred mean axis ratios for oblate, prolate, and triaxial (triaxials in two axis ratios), $μ_o=0.44, μ_p=0.72, μ_{t,β}=0.92, μ_{t,γ}=0.78$ where the fractions of oblate, prolate and triaxial types are \textrm{O:P:T}=0.29^{\pm0.09}:0.26^{\pm0.11}:0.45^{\pm0.13}$. We have also found that the luminous sample ($-23.3 < M_r \leq -21.2$) tends to have more triaxials than the less luminous ($-21.2 < M_r <-19.3$) sample does. Oblate is relatively more abundant among the less luminous galaxies. Interestingly, the preferences of axis ratios for triaxial types in the two luminosity classes are remarkably similar. We have not found any significant influence of the local galaxy number density on ARD. We show that the results can be seriously affected by the details in the data selection and type classification scheme. Caveats and implications on galaxy formation are discussed.

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