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arXiv 1611.01166astro-ph.GA
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COSMOS [ OII ]巡天:电子密度随恒星形成率的演化

The COSMOS [OII] Survey: Evolution of Electron Density with Star Formation Rate

Melanie Kaasinen, Fuyan Bian, Brent Groves, Lisa Kewley, Anshu Gupta

摘要:

在$z > 1$的恒星形成星系表现出显着不同的性质,以当地的星系相当的恒星质量。高红移的恒星形成星系不仅具有比本地星系更高的恒星形成率和气体分数,而且它们似乎拥有具有显着不同物理条件的恒星形成区域,包括更大的电子密度。为了了解什么物理机制是负责观察到的恒星形成条件的演变,我们组装了最大的恒星形成星系的样本在$z\sim 1.5$与发射线测量的$\mathrm{[OII]} λλ3726,3729$双重。通过比较我们的$z\sim 1.5$样本与当地星系样本的恒星质量,恒星形成率和特定的恒星形成率的等效分布,我们研究了电子密度的演化及其对全球性质的依赖性。我们测量了$z\sim 1.5$样本的平均电子密度为$114_{-27}^{+28} \, \mathrm {cm}^{-3} $,比本地恒星形成星系的典型电子密度大五倍。然而,我们没有发现本地和高红移星系的典型的电子密度之间的偏移与等效的恒星形成率。我们的工作表明,样品的平均电子密度是高度敏感的恒星形成率,这意味着以前观察到的演化主要是选择效应的结果。

英文摘要:

Star-forming galaxies at $z > 1$ exhibit significantly different properties to local galaxies of equivalent stellar mass. Not only are high-redshift star-forming galaxies characterized by higher star formation rates and gas fractions than their local counterparts, they also appear to host star-forming regions with significantly different physical conditions, including greater electron densities. To understand what physical mechanisms are responsible for the observed evolution of star-forming conditions we have assembled the largest sample of star-forming galaxies at $z\sim 1.5$ with emission-line measurements of the $\mathrm{[OII]} λλ3726,3729$ doublet. By comparing our $z\sim 1.5$ sample to local galaxy samples with equivalent distributions of stellar mass, star formation rate and specific star formation rate we investigate the proposed evolution in electron density and its dependence on global properties. We measure an average electron density of $114_{-27}^{+28} \, \mathrm {cm}^{-3} $ for our $z\sim 1.5$ sample, a factor of five greater than the typical electron density of local star-forming galaxies. However, we find no offset between the typical electron densities of local and high-redshift galaxies with equivalent star-formation rates. Our work indicates that the average electron density of a sample is highly sensitive to the star formation rates, implying that the previously observed evolution is mainly the result of selection effects.

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