Subaru Deep Survey. V. A Census of Lyman Break Galaxies at z ≃ 4 and 5 in the Subaru Deep Fields: Photometric Properties
Subaru Deep Survey. V. A Census of Lyman Break Galaxies at z ≃ 4 and 5 in the Subaru Deep Fields: Photometric Properties
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DOI：
10.1086/422207
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发表时间：
2004
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通讯作者：
M. Ouchi;K. Shimasaku;S. Okamura;H. Furusawa;N. Kashikawa;K. Ota;M. Doi;M. Hamabe;M. Kimura
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作者：
M. Ouchi;K. Shimasaku;S. Okamura;H. Furusawa;N. Kashikawa;K. Ota;M. Doi;M. Hamabe;M. Kimura
利用Subaru深场（SDF）和Subaru/XMM-牛顿深场（SXDF）的宽带B、V、R、i '和z'滤波器拍摄的深场（i′ = 27）和宽场（1200 arcmin ~ 2）图像，研究了z = 3.5-5.2的莱曼破裂星系（LBG）的光度学性质。LBG样品的选择标准与85光谱识别的对象进行检查，并估计从蒙特卡罗模拟的基础上的光度红移目录的哈勃深场北的样品的完整性和污染。我们发现，这些LBG样本几乎是静止坐标系的UV星等限制的样本，系统地丢失了只有10%的红色高z星系（数量），这是一个尘埃人口与E（B - V）0.4。我们计算了LBG的光度函数，发现（1）明亮星系（M1700 < -22 ;对应于SFR ≤ 100 h M/yr-1，带消光修正）的数密度从z = 4到5显著减小;（2）LBG的光度函数的暗端斜率可能随着红移的增加而变陡。我们从紫外连续谱的斜率估计了M < M ~*（λ-21）的z ~（14）LBG的尘埃消光，得到E（B - V）= 0.15 ± 0.03作为平均值。尘埃消光随表观光度保持不变，但随内在光度增加（即，校正的）光度。我们发现在z = 3和4的LBG之间的尘埃灭绝没有演变。我们通过积分LBG的LF来研究紫外光密度的演化，发现在1700 nm处的紫外光密度ρUV从z = 3到5没有显著变化，即，ρUV（z = 4）/ρUV（z = 3）= 1.0 ± 0.2和ρUV（z = 5）/ρUV（z = 3）= 0.8 ± 0.4;因此，宇宙星星形成率（SFR）密度（经尘埃消光校正）在误差条内保持不变，或者可能从z = 3到5略有下降。我们用这样得到的宇宙SFR估算了恒星的质量密度，发现这个质量密度与直接从恒星质量函数导出的质量密度在z = 0-1处是一致的，但比z ~ 3处的质量密度高3倍。我们发现，在z = 5时，Lyα发射体（LAEs）的紫外光密度与LBG的紫外光密度之比约为60%，因此约一半的星星形成可能发生在z = 5时的LAEs中。我们得到了对UV电离光子逃逸分数的约束（即，900 nm的UV连续谱），fesc ≤ 0.13。这意味着在z = 0时，LBG的逃逸分数可能大于恒星形成星系的逃逸分数。
We investigate the photometric properties of Lyman break galaxies (LBGs) at z = 3.5-5.2 based on large samples of 2600 LBGs detected in deep (i′ ≲ 27) and wide-field (1200 arcmin2) images taken in the Subaru Deep Field (SDF) and the Subaru/XMM-Newton Deep Field (SXDF) using broadband B, V, R, i', and z' filters. The selection criteria for the LBG samples are examined with 85 spectroscopically identified objects, and the completeness and contamination of the samples are estimated from Monte Carlo simulations based on a photometric-redshift catalog of the Hubble Deep Field-North. We find that these LBG samples are nearly rest-frame UV magnitude-limited samples, missing systematically only 10% of red high-z galaxies (in number), which are a dusty population with E(B - V) ≳ 0.4. We calculate luminosity functions (LFs) of the LBGs with the estimated completeness and contamination and find (1) that the number density of bright galaxies (M1700 < -22 ; corresponding to SFR ≳ 100 h M☉ yr-1 with extinction correction) decreases significantly from z = 4 to 5 and (2) that the faint-end slope of the LFs of LBGs may become steeper toward higher redshifts. We estimate the dust extinction of z ≃ 4 LBGs with M < M* (≃-21) from UV-continuum slopes and obtain E(B - V) = 0.15 ± 0.03 as the mean value. The dust extinction remains constant with apparent luminosity but increases with intrinsic (i.e., extinction-corrected) luminosity. We find no evolution in dust extinction between LBGs at z = 3 and 4. We investigate the evolution of UV-luminosity density by integrating the LFs of LBGs and find that the UV-luminosity density at 1700 Å, ρUV, does not significantly change from z = 3 to 5, i.e., ρUV(z = 4)/ρUV(z = 3) = 1.0 ± 0.2 and ρUV(z = 5)/ρUV(z = 3) = 0.8 ± 0.4; thus, the cosmic star formation rate (SFR) density (with correction for dust extinction) remains constant within the error bars, or possibly has a slight decline, from z = 3 to 5. We estimate the stellar mass density from the cosmic SFR thus obtained and find that this stellar mass density is consistent with those derived directly from the stellar mass function at z = 0-1 but exceeds those at z ~ 3 by a factor of 3. We find that the ratio of the UV-luminosity density of Lyα emitters (LAEs) to that of LBGs is ≃60% at z ≃ 5, and thus about half of star formation probably occurs in LAEs at z ≃ 5. We obtain a constraint on the escape fraction of UV ionizing photons (i.e., UV continuum in 900 Å) produced by LBGs, fesc ≳ 0.13. This implies that the escape fraction of LBGs may be larger than that of star-forming galaxies at z = 0.