Lyman-break galaxies at z ~ 5 – I. First significant stellar mass assembly in galaxies that are not simply z ~ 3 LBGs at higher redshift
Lyman-break galaxies at z ~ 5 – I. First significant stellar mass assembly in galaxies that are not simply z ~ 3 LBGs at higher redshift
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DOI：
10.1111/j.1365-2966.2007.11455.x
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发表时间：
2007-01
影响因子：
4.8
通讯作者：
A. Verma;M. Lehnert;N. F. Schreiber;M. Bremer;Laura Douglas Mpe;Garching;H Germany;U. Oxford;U.K.;U. Bristol
中科院分区：
文献类型：
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作者：
A. Verma;M. Lehnert;N. F. Schreiber;M. Bremer;Laura Douglas Mpe;Garching;H Germany;U. Oxford;U.K.;U. Bristol
我们利用钱德拉深场南区z ~ 5个Lyman-break星系（LBGs）的静帧紫外-可见光谱能量分布，确定了它们作为v波段dropouts至i AB < 26.3的系综性质。通过匹配选择并执行与z ~ 3样品相同的分析，我们发现在回看时间中相隔1 Gyr的两个LBGs样品的系综性质存在明显差异。我们发现z ~ 5 LBGs通常比z ~ 3 LBGs年轻得多（<100Myr），恒星质量（~ 10 9 M⊙）也比它们低（z ~ 3 LBGs通常是~ few x 10 10 M⊙，年龄为~ 320 Myr）。即使考虑到两个样本中存在年龄较大的潜在种群，质量差异也是显著的。这种年轻且中等质量的系统主导了z ~ 5 LBG群体（≥70%），而它们在z ~ 3 LBG样本中占≤30%。这一结果在所有合理的建模假设下都是稳健的，表明在z ~ 5和z ~ 3之间发光lbg的性质发生了明显的变化。这些年轻的、中等质量的z ~ 5 LBGs似乎正在经历第一代（几代）大规模恒星形成，并正在积累第一批重要的恒星质量。它们在发光LBG样品中的优势表明z ~ 5见证了一个广泛分布的近期星系形成时期。因此，z ~ 5 lbg很可能是当今大质量星系的球状成分的祖先。这是由它们的高恒星质量表面密度支持的，并且与它们的核心相空间密度，以及我们银河系和其他大质量系统中凸起的恒星的年龄一致。由于隐含的形成红移为z ~ 6 ~ 7，这些发光的z ~ 5 LBGs可能只在再电离结束时贡献了紫外光子预算。然而，它们每单位面积的高恒星形成率表明，这些系统拥有流出物或风，这些流出物或风使星系内和星系间介质富含金属，正如z ~ 3 LBGs所确定的那样。它们估计的年轻年龄与星系范围内低效率的金属混合一致。因此，这些星系可能包含Jiminez和Haimann提出的z ~ 3 LBGs中III星族恒星的很大一部分。
We determine the ensemble properties of z ∼ 5 Lyman-break galaxies (LBGs) selected as V-band dropouts to i AB < 26.3 in the Chandra Deep Field-South using their rest-frame UV-to-visible spectral energy distributions. By matching the selection and performing the same analysis that has been used for z ∼ 3 samples, we show clear differences in the ensemble properties of two samples of LBGs which are separated by 1 Gyr in look-back time. We find that z ∼ 5 LBGs are typically much younger (<100Myr) and have lower stellar masses (∼10 9 M ⊙ ) than their z ∼ 3 counterparts (which are typically ∼ few x 10 10 M ⊙ and ∼320 Myr old). The difference in mass is significant even when considering the presence of an older, underlying population in both samples. Such young and moderately massive systems dominate the luminous z ∼ 5 LBG population (≥70 per cent), whereas they comprise ≤30 per cent of LBG samples at z ∼ 3. This result, which we demonstrate is robust under all reasonable modelling assumptions, shows a clear change in the properties of the luminous LBGs between z ∼ 5 and z ∼ 3. These young and moderately massive z ∼ 5 LBGs appear to be experiencing their first (few) generations of large-scale star formation and are accumulating their first significant stellar mass. Their dominance in luminous LBG samples suggests that z ∼ 5 witnesses a period of wide-spread, recent galaxy formation. As such, z ∼ 5 LBGs are the likely progenitors of the spheroidal components of present-day massive galaxies. This is supported by their high stellar mass surface densities, and is consistent with their core phase-space densities, as well as the ages of stars in the bulge of our Galaxy and other massive systems. With implied formation redshifts of z ∼ 6-7, these luminous z ∼ 5 LBGs could have only contributed to the UV photon budget at the end of reionization. However, their high star formation rates per unit area suggest these systems host outflows or winds that enrich the intragalactic and intergalactic media with metals, as has been established for z ∼ 3 LBGs. Their estimated young ages are consistent with inefficient metal-mixing on galaxy-wide scales. Therefore these galaxies may contain a significant fraction of Population III stars as proposed for z ∼ 3 LBGs by Jiminez & Haimann.