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arXiv 1209.4084astro-ph.CO
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中等红移处的猝灭恒星形成:绿谷质量通量密度的减小

Quenching star formation at intermediate redshifts: downsizing of the mass flux density in the green valley

Thiago S. Gonçalves, D. Christopher Martin, Karín Menéndez-Delmestre, Ted Wyder, Anton Koekemoer

摘要:

星系性质的双峰性在低和高红移时都被观察到,在蓝色星云中的恒星形成星系和红色序列中的被动演化物体之间有明显的区别;没有具有中间性质的星系表明恒星形成的淬灭和随后的种群之间的转变必须迅速发生。在本文中,我们提出了一个研究超过100过境星系在所谓的“绿谷”在中等红移(z ~ 0.8)。通过使用凯克望远镜的DEIMOS仪器进行非常深的光谱学分析,我们能够推断出这些天体的恒星形成历史,并测量宇宙年龄为当前年龄一半时从蓝色云过渡到红色序列的恒星质量通量密度。我们的研究结果表明,这个过程发生得更快,过去的星系质量更大,这表明红色序列的大质量末端首先形成的是一种自上而下的情况。这代表了缩小的另一个方面,质量通量密度在最近向更小的星系移动。

英文摘要:

The bimodality in galaxy properties has been observed at low and high redshift, with a clear distinction between star-forming galaxies in the blue cloud and passively evolving objects in the red sequence; the absence of galaxies with intermediate properties indicates that the quenching of star formation and subsequent transition between populations must happen rapidly. In this paper, we present a study of over 100 transiting galaxies in the so-called "green valley" at intermediate redshifts (z ~ 0.8). By using very deep spectroscopy with the DEIMOS instrument at the Keck telescope we are able to infer the star formation histories of these objects and measure the stellar mass flux density transiting from the blue cloud to the red sequence when the universe was half its current age. Our results indicate that the process happened more rapidly and for more massive galaxies in the past, suggesting a top-down scenario in which the massive end of the red sequence is forming first. This represent another aspect of downsizing, with the mass flux density moving towards smaller galaxies in recent times.

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