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arXiv 1011.6569astro-ph.CO
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用深WFC3数据对红移~7的UV光度函数的临界分析

A critical analysis of the UV Luminosity Function at redshift~7 from deep WFC3 data

A. Grazian, M. Castellano, A. M. Koekemoer, A. Fontana, L. Pentericci, V. Testa, K. Boutsia, E. Giallongo, M. Giavalisco, P. Santini

摘要:

研究z=7的莱曼破缺星系(LBG)的光度函数(LF)对于确定它们在宇宙再电离中的作用具有重要意义。我们对z~7低频测定中的统计误差和系统误差进行了详细和严格的分析:我们收集了来自不同调查的z~7候选LBG的大样本,跨越了各种各样的区域和深度。特别是,我们结合了最近在HST上使用新的WFC 3近红外相机在GOODS-ERS和HUDF领域获得的深(J<27.4)和超深(J<29.2)调查数据,以及VLT和斯巴鲁在宽和浅区域的地基调查。我们使用z波段的公共ACS图像来选择z-dropout星系,并使用蓝色(BVI)和红色波段的其他公共数据来拒绝可能的低红移闯入者。我们将我们的结果与广泛的模拟进行了比较,以量化我们的选择标准的观测效果以及光度散射,颜色选择或候选人的形态的影响。我们发现z~7处的微弱LBG的数密度对所采用的颜色选择只有轻微的敏感性,但它强烈依赖于对模拟星系的半光分布所做的假设,用于校正观测样本的不完整性。由于z~7 LBG的物理尺寸分布未知,LBG LF的暗端的斜率因此具有相当大的不确定性。我们的结论是,在z~7的星系是无法recruitment宇宙,除非有一个显着的演变,在块状的IGM或在逃逸分数的电离光子,或者,有一个大的人口z~7的LBG与大的物理尺寸,但目前的观测仍然没有检测到。

英文摘要:

The study of the Luminosity Function (LF) of Lyman Break Galaxies (LBGs) at z=7 is important for ascertaining their role in the reionization of the Universe. We perform a detailed and critical analysis of the statistical and systematic errors in the z~7 LF determination: we have assembled a large sample of candidate LBGs at z~7 from different surveys, spanning a large variety of areas and depths. In particular, we have combined data from the deep (J<27.4) and ultradeep (J<29.2) surveys recently acquired with the new WFC3 NIR camera on HST, over the GOODS-ERS and the HUDF fields, with ground based surveys in wide and shallow areas from VLT and Subaru. We have used public ACS images in the z-band to select z-dropout galaxies, and other public data both in the blue (BVI) and in the red bands to reject possible low-redshift interlopers. We have compared our results with extensive simulations to quantify the observational effects of our selection criteria as well as the effects of photometric scatter, color selections or the morphology of the candidates. We have found that the number density of faint LBGs at z~7 is only marginally sensitive to the color selection adopted, but it is strongly dependent from the assumption made on the half light distributions of the simulated galaxies, used to correct the observed sample for incompleteness. The slope of the faint end of the LBGs LF has thus a rather large uncertainty, due to the unknown distribution of physical sizes of the z~7 LBGs. We conclude that galaxies at z~7 are unable to reionize the Universe unless there is a significant evolution in the clumpiness of the IGM or in the escape fraction of ionising photons or, alternatively, there is a large population of z~7 LBGs with large physical dimensions but still not detected by the present observations.

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