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z=0时蓝色恒星质量序列上的E/S0 Galerkin：衰落的合并还是未来的螺旋？

E/S0 Galaxies on the Blue Color-Stellar Mass Sequence at z=0: Fading Mergers or Future Spirals?

S. J. Kannappan, J. M. Guie, A. J. Baker

备注：
AJ, submitted, revised, 21 pages with 15 figures (one in two parts, one color); full resolution version available at http://www.physics.unc.edu/~sheila/kgb.pdf
发表信息：
Astron.J.138:579,2009
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摘要：

我们确定了人口的形态定义的E/S 0星系躺在蓝色序列在本时代。我们使用三个样本分析了恒星质量大于10^8 Msun的蓝色序列E/S 0，认为单个天体可能向上朝着红色序列演化，也可能向下朝着蓝色序列演化。蓝色序列E/S 0星系随着恒星质量的减小而变得更加常见，在“关闭质量”M_s ~ 1-2 x 10^11 Msun附近，E/S 0的含量小于2%，在“双峰质量”M_b ~ 3 x 10^10 Msun附近，E/S 0的含量增加到>5%，在“阈值质量”M_t ~ 4-6 x 10^9 Msun以下，E/S 0的含量急剧增加到>20-30%。蓝序E/S 0 s在M_t以下的强烈出现与先前报道的两个序列上所有类型星系在M_t以下的平均原子气体分数的全球增加相吻合，这表明冷气体的可用性可能是蓝序E/S 0 s存在的基础。环境分析表明，许多亚M_b蓝序列E/S 0存在于低至中等密度环境中。在质量-半径和质量-西格玛标度关系中，蓝序E/S 0与红序E/S 0比晚型星系更相似，但它们代表了一个过渡类。虽然其中一些，特别是在M_b到M_s的高质量范围内，类似于可能会消失在红色序列上的主要合并残留物，但大多数低于M_b的蓝色序列E/S 0显示出盘和/或假隆起形成的迹象，这可能会被同伴相互作用增强。我们认为，亚M_b蓝序E/S 0在恒星质量和浓度上占据了一个“最佳点”，既有丰富的气体，又有最佳的恒星形成效率，这可能使大螺旋盘的形成成为可能。[删节]

英文摘要：

We identify a population of morphologically defined E/S0 galaxies lying on the blue sequence at the present epoch. Using three samples, we analyze blue-sequence E/S0s with stellar masses >10^8 Msun, arguing that individual objects may be evolving either up toward the red sequence or down into the blue sequence. Blue-sequence E/S0 galaxies become more common with decreasing stellar mass, comprising <2% of E/S0s near the "shutdown mass" M_s ~ 1-2 x 10^11 Msun, increasing to >5% near the "bimodality mass" M_b ~ 3 x 10^10 Msun, and sharply rising to >20-30% below the "threshold mass" M_t ~ 4-6 x 10^9 Msun. The strong emergence of blue-sequence E/S0s below M_t coincides with a previously reported global increase in mean atomic gas fractions below M_t for galaxies of all types on both sequences, suggesting that the availability of cold gas may be basic to blue-sequence E/S0s' existence. Environmental analysis reveals that many sub-M_b blue-sequence E/S0s reside in low to intermediate density environments. In mass-radius and mass-sigma scaling relations, blue-sequence E/S0s are more similar to red-sequence E/S0s than to late-type galaxies, but they represent a transitional class. While some of them, especially in the high-mass range from M_b to M_s, resemble major-merger remnants that will likely fade onto the red sequence, most blue-sequence E/S0s below M_b show signs of disk and/or pseudobulge building, which may be enhanced by companion interactions. We argue that sub-M_b blue-sequence E/S0s occupy a "sweet spot" in stellar mass and concentration, with both abundant gas and optimally efficient star formation, which may enable the formation of large spiral disks. [abridged]

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