COSMOS中棒分数的演化：量化哈勃序列的组装
Evolution of the Bar Fraction in COSMOS: Quantifying the Assembly of the Hubble Sequence
摘要：
我们分析了COSMOS 2平方度视场中2,157个发光的正面螺旋星系中0.2<z<0.84以上的星系棒的红移依赖比例。我们的样本是一个数量级大于在任何以前的调查中使用的，是基于更深的成像数据比早期的广域研究高红移星系形态。我们发现，随着红移的增加，棒旋的分数迅速下降。然而在本星系中，大约65%的明亮螺旋星系包含棒（SB+SAB），在z ~0.84时，这一比例下降到大约20%。在这个红移范围内，强（SB）棒的比例从大约30%下降到10%以下。很明显，当宇宙是现在年龄的一半时，哈勃序列上的星系普查与现在的星系普查有着根本的不同。从我们的分析中也出现了理解这种现象的一个主要线索，它表明螺旋星系中的棒分数是恒星质量，综合颜色和凸起突出的强函数。在质量很大的明亮螺旋星系中，棒分数在z ~ 0.84范围内是恒定的，而对于质量较低的蓝色螺旋星系，当红移超过z=0.3时，棒分数显著下降。在高红移下，在以凸起为主的系统中，也有一种轻微的偏好，这可能是一个重要的线索，对棒，凸起和黑洞的共同演化。因此，我们的研究结果有重要的后果负责星系缩小的过程中，这表明，大质量星系成熟早在动力学意义上，而不仅仅是作为其恒星形成率的调节结果。
英文摘要：
We have analyzed the redshift-dependent fraction of galactic bars over 0.2<z<0.84 in 2,157 luminous face-on spiral galaxies from the COSMOS 2-square degree field. Our sample is an order of magnitude larger than that used in any previous investigation, and is based on substantially deeper imaging data than that available from earlier wide-area studies of high-redshift galaxy morphology. We find that the fraction of barred spirals declines rapidly with redshift. Whereas in the local Universe about 65% of luminous spiral galaxies contain bars (SB+SAB), at z ~0.84 this fraction drops to about 20%. Over this redshift range the fraction of strong (SB) bars drops from about 30% to under 10%. It is clear that when the Universe was half its present age, the census of galaxies on the Hubble sequence was fundamentally different from that of the present day. A major clue to understanding this phenomenon has also emerged from our analysis, which shows that the bar fraction in spiral galaxies is a strong function of stellar mass, integrated color and bulge prominence. The bar fraction in very massive, luminous spirals is about constant out to z ~ 0.84 whereas for the low mass, blue spirals it declines significantly with redshift beyond z=0.3. There is also a slight preference for bars in bulge dominated systems at high redshifts which may be an important clue towards the co-evolution of bars, bulges and black holes. Our results thus have important ramifications for the processes responsible for galactic downsizing, suggesting that massive galaxies matured early in a dynamical sense, and not just as a result of the regulation of their star formation rate.
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