COLORS AND COLOR GRADIENTS IN BULGES OF GALAXIES
COLORS AND COLOR GRADIENTS IN BULGES OF GALAXIES
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星系核球中的颜色和颜色梯度
DOI：
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发表时间：
1993
期刊：
影响因子：
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通讯作者：
R. Peletier
中科院分区：
文献类型：
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作者：
M. Balcells;R. Peletier
我们对45个早型旋涡星系的完整光选样品进行了U、B、R和I波段的表面测光，以研究旋涡星系球的颜色和颜色梯度。在半短轴上的楔形开口中，已经确定了U-R、B-R、U-B和R-I的颜色分布。基于几个标准，如颜色轮廓的平滑度，没有灰尘带，以及中心颜色，我们定义了一个18个物体的子样本，其颜色基本上不受灰尘的影响。我们相信这样的颜色是适合于推断的性质的恒星人口的凸起。我们发现，突出的颜色主要是蓝色比椭圆。这个结果甚至在将球拱与相同光度的椭圆星系比较时也成立，并且表明球拱比老椭圆星系更年轻和/或更贫金属。大多数的凸起都达不到太阳的金属丰度。凸起主要显示负颜色梯度（向外变蓝）。对于明亮的凸起（M（R）Bulge - 20），明显的颜色梯度的存在表明了不同的形成机制。对于这些物体，盘的存在可能严重影响了凸起的径向人口分布。
We have obtained surface photometry in U, B, R, and I for a complete optically selected sample of 45 early-type spiral galaxies, to investigate the colors and color gradients of spiral bulges. Color profiles in U-R, B-R, U-B, and R-I have been determined in wedges opening on the semiminor axes. Based on several criteria, like the smoothness of the color profiles, the absence of dust lanes, and the central colors, we have defined a subsample of 18 objects whose colors are largely unaffected by dust. We believe such colors are suitable for inferring properties of the stellar populations of bulges. We find that the colors of bulges are predominantly bluer than those of ellipticals. This result holds even when bulges are compared to ellipticals of the same luminosity, and indicates that bulges are younger and/or more metal poor than old elliptical galaxies. Most bulges do not reach solar metallicities. Bulges show predominantly negative color gradients (bluer outward). For bright bulges (M(R)Bulge - 20), the existence of pronounced color gradients suggests a different formation mechanism. For these objects, the presence of the disk may have severely affected the radial population distribution in the bulge.