Spitzer IRAC Confirmation of z850-Dropout Galaxies in the Hubble Ultra Deep Field: Stellar Masses and Ages at z ≈ 7
Spitzer IRAC Confirmation of z850-Dropout Galaxies in the Hubble Ultra Deep Field: Stellar Masses and Ages at z ≈ 7
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DOI：
10.1086/508512
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发表时间：
2006-08
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影响因子：
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通讯作者：
I. Labbé;R. Bouwens;G. Illingworth;M. F. C. Observatories;Ucolick UC Santa Cruz;L. Observatory
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文献类型：
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作者：
I. Labbé;R. Bouwens;G. Illingworth;M. F. C. Observatories;Ucolick UC Santa Cruz;L. Observatory
使用斯皮策IRAC中红外成像从大天文台起源深调查，我们研究z 850辍学源在哈勃超深场。在仔细地从前景源中去除污染通量后，我们清楚地检测到两个z 850在3.6和4.5 μm处的漏失，而另外两个漏失是勉强检测到的。中红外线通量强有力地支持了对它们的解释，即它们是z = 1.7的星系，而宇宙的年龄只有7.5亿年。IRAC的观测使我们第一次能够限制最高红移星系的静止坐标系光学颜色、恒星质量和年龄。用光谱能量分布拟合星族模型，我们发现光度红移在6.7-7.4范围内，静止坐标系色U-V = 0.2-0.4，V波段光度LV = 0.5 - 0.5。（0.6-3）× 1010 L，恒星质量（1-10）× 109 M，恒星年龄50-200 Myr，星星形成速率高达~25 M yr-1，低红化AV < 0.4。总的来说，z = 7的星系看起来比z = 2-3的莱曼破裂星系或遥远的红星系质量要小得多，但与最近发现的z = 5-6的系统相当相似。从我们的z = 7样本中推断出的恒星质量密度为ρ* = 1.6 × 106 M/Mpc-3（至0.3L），与最近的宇宙学流体动力学模拟明显一致，但我们注意到，不完整性和样本方差可能会引入更大的不确定性。这两个最大质量星系的年龄表明，它们形成于z 108，在宇宙再电离的时代，但从它们的恒星质量和年龄得出的星星形成率密度几乎不足以使宇宙再电离。对这种缺陷最简单的解释是，超出我们探测极限的低质量星系使宇宙再电离。
Using Spitzer IRAC mid-infrared imaging from the Great Observatories Origins Deep Survey, we study z850-dropout sources in the Hubble Ultra Deep Field. After carefully removing contaminating flux from foreground sources, we clearly detect two z850 dropouts at 3.6 and 4.5 μm, while two others are marginally detected. The mid-infrared fluxes strongly support their interpretation as galaxies at z ≈ 7, seen when the universe was only 750 Myr old. The IRAC observations allow us for the first time to constrain the rest-frame optical colors, stellar masses, and ages of the highest redshift galaxies. Fitting stellar population models to the spectral energy distributions, we find photometric redshifts in the range 6.7-7.4, rest-frame colors U - V = 0.2-0.4, V-band luminosities LV = (0.6-3) × 1010 L☉, stellar masses (1-10) × 109 M☉, stellar ages 50-200 Myr, star formation rates up to ~25 M☉ yr-1, and low reddening AV < 0.4. Overall, the z = 7 galaxies appear substantially less massive and evolved than Lyman break galaxies or distant red galaxies at z = 2-3, but fairly similar to recently identified systems at z = 5-6. The stellar mass density inferred from our z = 7 sample is ρ* = 1.6 × 106 M☉ Mpc-3 (to 0.3L), in apparent agreement with recent cosmological hydrodynamic simulations, but we note that incompleteness and sample variance may introduce larger uncertainties. The ages of the two most massive galaxies suggest that they formed at z ≳ 8, during the era of cosmic reionization, but the star formation rate density derived from their stellar masses and ages is not nearly sufficient to reionize the universe. The simplest explanation for this deficiency is that lower mass galaxies beyond our detection limit reionized the universe.