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arXiv 1608.07280astro-ph.GA
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Ly $α$ -发射体在$z\sim2.5$处的静止框架光谱性质:强Ly $α$发射的物理起源

The Rest-Frame Optical Spectroscopic Properties of Ly$α$-Emitters at $z\sim2.5$: The Physical Origins of Strong Ly$α$ Emission

Ryan F. Trainor, Allison L. Strom, Charles C. Steidel, Gwen C. Rudie

摘要:

本文给出了60个弱($R_{AB}\sim 27$ ; $L\sim0.1 L_*$)Ly $α$选择星系(LAEs)在$z\approx2.56$的静止标架光谱。平均LAE与$z\approx2-3$连续选择星系分布的极端低金属丰度端一致。特别是,LAE具有极高的[OIII] PDMATHAMR 5008/H PDMATHAMS比率(log([OIII]/H PDMATHAMS)PDMATHAMT 0.8)和低[NII] PDMATHAMR 6585/H PDMATHAMO比率(log([NII]/H PDMATHAMO)$<-1.15$)。使用[OIII] $λ$ 4364极光线,我们发现,在昏暗的LAEs的恒星形成区域的特点是高电子温度($T_e\approx1.8\times10^4$ K),低氧丰度(12 + log(O/H)$\approx$ 8.04,$Z_{neb}\approx0.22Z_\odot$),和高激发相对于更明亮的星系。我们最微弱的LAE具有与甚至更低的金属丰度一致的线比率,包括6个具有12 + log(O/H)$\approx$ 6.9 $-$ 7.4($Z_{neb}\approx0.02-0.05Z_\odot$)的线比率。我们根据恒星演化的新模型(包括二元相互作用)来解释这些观测结果。我们发现,强大的,硬电离连续需要重现我们观察到的线比,这表明微弱的星系是电离光子和再电离时代的星系的重要类似物的有效生产者。此外,我们调查的物理趋势,伴随着Ly $α$发射在最大的电流样本相结合的Ly $α$和休息光学星系光谱,包括60个微弱的LAEs和368个更明亮的星系在类似的红移。我们发现,Ly $α$发射与星云激发和电离强烈相关,与尘埃衰减弱相关,这表明金属丰度在确定这些星系的观测特性中起着重要作用,通过调制它们的恒星光谱,星云激发和尘埃含量。

英文摘要:

We present rest-frame optical spectra of 60 faint ($R_{AB}\sim 27$; $L\sim0.1 L_*$) Ly$α$-selected galaxies (LAEs) at $z\approx2.56$. The average LAE is consistent with the extreme low-metallicity end of the continuum-selected galaxy distribution at $z\approx2-3$. In particular, the LAEs have extremely high [OIII] $λ$5008/H$β$ ratios (log([OIII]/H$β$) $\sim$ 0.8) and low [NII] $λ$6585/H$α$ ratios (log([NII]/H$α$) $<-1.15$). Using the [OIII] $λ$4364 auroral line, we find that the star-forming regions in faint LAEs are characterized by high electron temperatures ($T_e\approx1.8\times10^4$K), low oxygen abundances (12 + log(O/H) $\approx$ 8.04, $Z_{neb}\approx0.22Z_\odot$), and high excitations with respect to more luminous galaxies. Our faintest LAEs have line ratios consistent with even lower metallicities, including six with 12 + log(O/H) $\approx$ 6.9$-$7.4 ($Z_{neb}\approx0.02-0.05Z_\odot$). We interpret these observations in light of new models of stellar evolution (including binary interactions). We find that strong, hard ionizing continua are required to reproduce our observed line ratios, suggesting that faint galaxies are efficient producers of ionizing photons and important analogs of reionization-era galaxies. Furthermore, we investigate physical trends accompanying Ly$α$ emission across the largest current sample of combined Ly$α$ and rest-optical galaxy spectroscopy, including 60 faint LAEs and 368 more luminous galaxies at similar redshifts. We find that Ly$α$ emission is strongly correlated with nebular excitation and ionization and weakly correlated with dust attenuation, suggesting that metallicity plays a strong role in determining the observed properties of these galaxies by modulating their stellar spectra, nebular excitation, and dust content.

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