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arXiv 0907.4766astro-ph.CO
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论局域宇宙中致密大质量红序星系的存在

On the Dearth of Compact, Massive, Red Sequence Galaxies in the Local Universe

Edward N Taylor, Marijn Franx, Karl Glazebrook, Jarle Brinchmann, Arjen van der Wel, Pieter G van Dokkum

摘要:

利用斯隆数字巡天(SDSS;数据发布7)的数据,我们已经进行了一个搜索的本地类似的非常紧凑,巨大的,静止的星系已被确定在z > 2。我们发现,不完整性是这样的紧凑的星系,特别是低红移(z < ~0.05)的SDSS光谱目标选择算法的结果关注。我们已经确定了63个0.066 < z < 0.12的大质量红色序列星系,它们比中等大小-质量关系小2倍或更多。与维里定理的预期一致,这些星系的质量-速度色散关系的中值偏移为0.12 dex。我们没有发现任何星系的大小和质量可以与z ~ 2观测到的星系相比,这意味着同动数密度(在固定大小和质量下)减少了5000倍以上。这一结果不能用不完整性来解释:在0.066 < z <0.12时,对于在高红移下看到的大小和质量的星系,SDSS光谱样本通常应该是~75%完整,尽管对于非常小的星系,它可能低至~ 20%。为了证实SDSS中没有这种致密的大质量星系不是光谱选择效应,我们也在SDSS光度表中寻找这样的星系,使用光度红移。虽然我们确实发现了对大质量紧凑星系的偏见的迹象,但这种分析表明,SDSS光谱样本在我们考虑的范围内最多缺少几个物体。接受高红移的结果,很明显,大质量星系必须在z<2的范围内经历显著的结构演化,才能与在本地宇宙中看到的人口相匹配。我们的研究结果表明,一个高度随机的机制,如主要的合并不能成为这种强大的规模演变的主要驱动力。

英文摘要:

Using data from the Sloan Digital Sky Survey (SDSS; data release 7), we have conducted a search for local analogs to the extremely compact, massive, quiescent galaxies that have been identified at z > 2. We show that incompleteness is a concern for such compact galaxies, particularly for low redshifts (z < ~0.05) as a result of the SDSS spectroscopic target selection algorithm. We have identified 63 massive red sequence galaxies at 0.066 < z < 0.12 that are smaller than the median size-mass relation by a factor of 2 or more. Consistent with expectations from the virial theorem, the median offset from the mass-velocity dispersion relation for these galaxies is 0.12 dex. We do not find any galaxies with sizes and masses comparable to those observed at z ~ 2, implying a decrease in the comoving number density (at fixed size and mass) by a factor of > 5000. This result cannot be explained by incompleteness: at 0.066 < z <0.12, the SDSS spectroscopic sample should typically be ~75% complete for galaxies with the sizes and masses seen at high redshift, although for the very smallest galaxies it may be as low as ~20%. To confirm that the absence of such compact massive galaxies in SDSS is not a spectroscopic selection effect, we have also looked for such galaxies in the SDSS photometric catalog, using photometric redshifts. While we do find signs of a bias against massive, compact galaxies, this analysis suggests that the SDSS spectroscopic sample is missing at most a few objects in the regime we consider. Accepting the high redshift results, it is clear that massive galaxies must undergo significant structural evolution over z<2 in order to match the population seen in the local universe. Our results suggest that a highly stochastic mechanism like major mergers cannot be the primary driver of this strong size evolution.

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