The VANDELS survey: the ionizing properties of star-forming galaxies at 3 = z = 5 using deep rest-frame ultraviolet spectroscopy
The VANDELS survey: the ionizing properties of star-forming galaxies at 3 = z = 5 using deep rest-frame ultraviolet spectroscopy
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VANDELS 调查：使用深度静止框架紫外光谱分析 3 = z = 5 处恒星形成星系的电离特性
DOI：
10.1093/mnras/stad1283
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发表时间：
2023
影响因子：
4.8
通讯作者：
Saldana-Lopez A
中科院分区：
文献类型：
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作者：
Saldana-Lopez A
再电离时代(EOR)星系的物理性质仍然很难受到观测的限制。为了更好地了解ESOVANDELS光谱测量中星系的电离性质，我们研究了从公开的≃-VANDELS光谱测量中选择的3≤z≤5处的ESO500星形成星系的深层静止框架紫外线(UV)光谱。绝对电离光子逃逸分数(即泄漏与产生的电离光子的比率)是通过将吸收线测量与紫外线衰减估计相结合而得到的。电离产生效率(ξ离子，即每个非电离紫外光度产生的电离光子数)是通过对范德尔斯星系的远紫外光(FUV)恒星连续体进行拟合来计算的。我们发现，对于低质量、蓝色UV连续谱斜率和发射强Lyξ的星系，两个离子参数都增加了，并且都略高于样本中UV最弱星系的平均值。潜在的莱曼连续谱发射体(LCES)和选定的莱曼阿尔法发射体(LAES，Wlyα≤−20 ä)在相似的紫外线强度下系统地表现出比非LCES和非LAE(ξ ξIon(Hz Erg−1)≈25.18，25.14)更高的对数离子(Log ξIon(Hz Erg−1)≈25.38，25.41)。这表明潜在恒星群非常年轻(≈10 MYR)，金属度相对较低(≈0.2Z⊙)。潜在LCE的全紫外非电离光谱的特征是蓝紫外斜率(≤−2)、增强的Ly α发射(≤−25 ？)、强的UV星云线(如高的$\rM C\，\小的{IV}}$1550/$\rM C\，\小的{III}}$1908≥0.75)和弱的吸收线(≤1 ？)。后者表明星际介质中存在低气柱密度的通道，这使得电离光子能够逃逸。通过将我们的VANDELS结果与文献中的其他调查结果进行比较，我们的发现表明EOR中的电离预算很可能是由紫外线微弱、低质量和无尘埃的星系主导的。
The physical properties of Epoch of Reionization (EoR) galaxies are still poorly constrained by observations. To better understand the ionizing properties of galaxies in the EoR, we investigate deep, rest-frame ultraviolet (UV) spectra of ≃500 star-forming galaxies at 3 ≤z≤ 5 selected from the public ESO-VANDELS spectroscopic survey. The absolute ionizing photon escape fraction (, i.e. the ratio ofleakingagainstproducedionizing photons) is derived by combining absorption line measurements with estimates of the UV attenuation. The ionizing production efficiency (ξion, i.e. the number of ionizing photons produced per non-ionizing UV luminosity) is calculated by fitting the far-UV (FUV) stellar continuum of the VANDELS galaxies. We find that theand ξionparameters increase towards low-mass, blue UV-continuum slopes and strong Ly α emitting galaxies, and both are slightly higher-than-average for the UV-faintest galaxies in the sample. Potential Lyman Continuum Emitters (LCEs,) and selected Lyman Alpha Emitters (LAEs,WLyα≤ −20 Å) show systematically higher ξion(log ξion(Hz erg−1) ≈ 25.38, 25.41) than non-LCEs and non-LAEs (log ξion(Hz erg−1) ≈ 25.18, 25.14) at similar UV magnitudes. This indicates very young underlying stellar populations (≈10 Myr) at relatively low metallicities (≈0.2 Z⊙). The FUV non-ionizing spectra of potential LCEs is characterized by blue UV slopes (≤−2), enhanced Ly α emission (≤−25 Å), strong UV nebular lines (e.g. high ${\rm C\, \small {IV}}$1550/${\rm C\, \small {III}}$1908 ≥0.75 ratios), and weak absorption lines (≤1 Å). The latter suggests the existence of low gas-column-density channels in the interstellar medium, which enables the escape of ionizing photons. By comparing our VANDELS results against other surveys in the literature, our findings imply that the ionizing budget in the EoR was likely dominated by UV-faint, low-mass, and dustless galaxies.