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arXiv 0802.0877astro-ph
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斯隆数字巡天中星系的形状

The shapes of galaxies in the Sloan Digital Sky Survey

Nelson D. Padilla, Michael A. Strauss

摘要:

我们确定的螺旋和椭圆星系的基本形状在斯隆数字巡天数据发布6从观测到的分布投影星系的形状,考虑到尘埃消光和变红的影响。我们假设螺旋和椭圆的基本形状可以很好地近似为三轴椭球。椭圆星系的数据与扁球体一致,光度与椭圆率之间存在相关性:Mr ~ -18椭圆星系的短轴与中轴之比平均值为0.41 ± 0.03,Mr ~-22.5椭圆星系的短轴与中轴之比平均值为0.76 ± 0.04。椭圆星系的轴比几乎没有依赖于星系的颜色,这意味着可以忽略不计的尘埃光学厚度。螺旋星系的形状有很大的变化,颜色表明尘埃的存在。在SDSS-DR 6中,旋涡星系的内部形状与平均厚度直径比为(21+-2)%,表面椭圆率e为ln(e)=-2.33+-0.79的扁平盘一致。在模型中不包括灰尘的影响,会导致磁盘系统地变圆高达60%。更明亮的螺旋星系往往比光度较低的螺旋星系有更厚更圆的盘。对于较大的星系来说,椭圆星系和螺旋星系都倾向于更圆。旋涡星系边缘r带尘埃消光E_0的边缘值,对于中色星系为E_0 ~ 0.45等,对于g-r>0.9的星系为E_0=1等,对于半光半径<2kpc/h的明亮和最致密的星系为E_0=1.9等。

英文摘要:

We determine the underlying shapes of spiral and elliptical galaxies in the Sloan Digital Sky Survey Data Release 6 from the observed distribution of projected galaxy shapes, taking into account the effects of dust extinction and reddening. We assume that the underlying shapes of spirals and ellipticals are well approximated by triaxial ellipsoids. The elliptical galaxy data are consistent with oblate spheroids, with a correlation between luminosity and ellipticity: the mean values of minor to middle axis ratios are 0.41+-0.03 for Mr ~ -18 ellipticals, and 0.76+-0.04 for Mr ~-22.5 ellipticals. Ellipticals show almost no dependence of axial ratio on galaxy colour, implying a negligible dust optical depth. There is a strong variation of spiral galaxy shapes with colour indicating the presence of dust. The intrinsic shapes of spiral galaxies in the SDSS-DR6 are consistent with flat disks with a mean and dispersion of thickness to diameter ratio of (21+-2)%, and a face-on ellipticity, e, of ln(e)=-2.33+-0.79. Not including the effects of dust in the model leads to disks that are systematically rounder by up to 60%. More luminous spiral galaxies tend to have thicker and rounder disks than lower-luminosity spirals. Both elliptical and spiral galaxies tend to be rounder for larger galaxies. The marginalised value of the edge-on r-band dust extinction E_0 in spiral galaxies is E_0 ~ 0.45 magnitudes for galaxies of median colours, increasing to E_0=1 magnitudes for g-r>0.9 and E_0=1.9 for the luminous and most compact galaxies, with half-light radii <2kpc/h.

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