Smoothly rising star formation histories during the reionization epoch
Smoothly rising star formation histories during the reionization epoch
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DOI：
10.1111/j.1365-2966.2010.17554.x
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发表时间：
2010-05
影响因子：
4.8
通讯作者：
K. Finlator;B. Oppenheimer;R. Dav'e
中科院分区：
文献类型：
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作者：
K. Finlator;B. Oppenheimer;R. Dav'e
宇宙流体动力学模拟有力地预测，高红移星系恒星形成历史(SFH)正在平稳上升，并且只随质量变化一个标度因子。我们使用我们最新的模拟来测试这种情景是否可以解释最近来自WFC3/IR、NICMOS和IRAC在z≥6的观测。我们的模拟广泛地再现了观测到的紫外光度函数和恒星质量密度及其在z=6-8时的演化，所有这些都是对平均SFH的非平凡检验。与观测结果一致的是，模拟星系由于年龄年轻(50-150Myr)、低金属丰度(0.1Z-0.5Z⊙)和低尘埃柱[E(B-V)<；0.05]而具有蓝色UV连续性。我们预测的在z=7时的巴尔默破裂虽然很重要，但即使在考虑星云线发射之后，也比观测到的弱0.5mag，这表明观测系统误差和/或数值分辨率的限制。观测结果表明，在z=6-8的范围内，恒星质量-恒星形成速率关系的斜率接近于1，证实了SFH形状不变的预测。尘埃消光对UV光度密度的抑制为2-3倍，由于金属度的增加，抑制程度在以后略有增加。目前的观测探测到大多数恒星质量超过109M⊙的星系和少数质量小于108.5M⊙的星系，这意味着它们探测的恒星质量不超过最亮的≈30%的完整恒星形成和z≥6时的恒星质量密度。最后，我们证明了平稳上升的SFH和最近的星团观测之间没有冲突。这是因为动量驱动的外流抑制了低质量晕中的恒星形成，因此即使恒星形成的占空比是1，容纳可观测星系的晕的比例(占有率)是0.2-0.4。这导致了在z≥4上的许多有趣的预测，其中包括：(1)光学选择和UV选择的样本在很大程度上重叠；(2)很少有星系表现出明显的特定恒星形成速率被抑制；以及(3)占有率随着光度的降低而恒定或增加。这些预测与目前的观察结果初步一致，但需要对现有和即将到来的数据集进行进一步分析，以便更彻底地检验它们。
Cosmological hydrodynamic simulations robustly predict that high-redshift galaxy star formation histories (SFHs) are smoothly rising and vary with mass only by a scalefactor. We use our latest simulations to test whether this scenario can account for recent observations at z ≥ 6 from WFC3/IR, NICMOS and IRAC. Our simulations broadly reproduce the observed ultraviolet (UV) luminosity functions and stellar mass densities and their evolution at z = 6-8, all of which are non-trivial tests of the mean SFH. In agreement with observations, simulated galaxies possess blue UV continua owing to young ages (50-150 Myr), low metallicities (0.1-0.5 Z ⊙ ) and low dust columns [E(B - V) < 0.05]. Our predicted Balmer breaks at z = 7, while significant, are ≈0.5 mag weaker than observed even after accounting for nebular line emission, suggesting observational systematic errors and/or numerical resolution limitations. Observations imply a near-unity slope in the stellar mass-star formation rate relation at all z = 6-8, confirming the prediction that SFH shapes are invariant. Dust extinction suppresses the UV luminosity density by a factor of 2-3, with suppression increasing modestly to later times owing to increasing metallicities. Current surveys detect the majority of galaxies with stellar masses exceeding 10 9 M ⊙ and few galaxies less massive than 10 8.5 M ⊙ , implying that they probe no more than the brightest ≈30 per cent of the complete star formation and stellar mass densities at z ≥ 6. Finally, we demonstrate that there is no conflict between smoothly rising SFHs and recent clustering observations. This is because momentum-driven outflows suppress star formation in low-mass haloes such that the fraction of haloes hosting observable galaxies (the 'occupancy') is 0.2-0.4 even though the star formation duty cycle is unity. This leads to many interesting predictions at z ≥ 4, among them that (1) optically selected and UV-selected samples largely overlap; (2) few galaxies exhibit significantly suppressed specific star formation rates; and (3) occupancy is constant or increasing with decreasing luminosity. These predictions are in tentative agreement with current observations, but further analysis of existing and upcoming data sets is required in order to test them more thoroughly.