arXiv 2007.121972020-07astro-ph.GA

在$1.3<z<3.7$极端[ OIII ]发射体的静止框架UV光谱学：朝向JWST的高红移UV参考样品

Rest-frame UV spectroscopy of extreme [OIII] emitters at $1.3<z<3.7$: Toward a high-redshift UV reference sample for JWST

Mengtao Tang, Daniel Stark, Jacopo Chevallard, Stéphane Charlot, Ryan Endsley, Enrico Congiu

备注：: 21 pages, 10 figures, accepted by MNRAS
DOI：: 10.1093/mnras/staa3454

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摘要：

星系再电离时代的深层光谱学揭示了强烈的CIII]和CIV线发射（EW $>15-20$）。为了解释在$z>6$出现的星云发射，我们已经开始瞄准在$1.3<z<3.7$具有大的比恒星形成率（sSFR）的星系中的静止帧UV发射线。我们发现，CIII]达到EWs在$z>6$看到只有在大sSFR星系与[OIII]+H $β$ EW $>1500$的。与以前的研究相比，我们发现许多具有强烈[OIII]的星系具有弱的CIII]发射（EW $=5-8$），这表明与年轻恒星群体相关的辐射场不足以为强CIII]提供动力。光电离模型表明，在具有大sSFR（[OIII]+H $β$ EW $>1500$）的系统中，CIII]的扩散是由金属丰度的变化驱动的，这是CIII]对电子温度极端敏感的结果。我们发现，在$z>6$（EW $>15$）处看到的强CIII]发射需要贫金属气体（$\simeq0.1\ Z_\odot$），而在我们的样品中较弱的CIII]发射倾向于在中等金属丰度（$\simeq0.3\ Z_\odot$）处发现。我们的$z\simeq1-3$样品中CIII]发射体的光度分布呈现出一致的图像，较强的发射通常与低光度系统（$M_{\rm{UV}}>-19.5$）有关，其中低金属丰度更有可能。我们定量了强CIII]和CIV发射体在$z\simeq1-3$的分数，提供了与$z>6$样品进行比较的基线。我们认为，在$z>6$的第一紫外线检测可以解释，如果一个显着的部分早期星系人口被发现在大sSFR（$>200$陀螺$^{-1}$）和低金属丰度（$<0.1\ Z_\odot$）。

英文摘要：

Deep spectroscopy of galaxies in the reionization-era has revealed intense CIII] and CIV line emission (EW $>15-20$ Å). In order to interpret the nebular emission emerging at $z>6$, we have begun targeting rest-frame UV emission lines in galaxies with large specific star formation rates (sSFRs) at $1.3<z<3.7$. We find that CIII] reaches the EWs seen at $z>6$ only in large sSFR galaxies with [OIII]+H$β$ EW $>1500$ Å. In contrast to previous studies, we find that many galaxies with intense [OIII] have weak CIII] emission (EW $=5-8$ Å), suggesting that the radiation field associated with young stellar populations is not sufficient to power strong CIII]. Photoionization models demonstrate that the spread in CIII] among systems with large sSFRs ([OIII]+H$β$ EW $>1500$ Å) is driven by variations in metallicity, a result of the extreme sensitivity of CIII] to electron temperature. We find that the strong CIII] emission seen at $z>6$ (EW $>15$ Å) requires metal poor gas ($\simeq0.1\ Z_\odot$) whereas the weaker CIII] emission in our sample tends to be found at moderate metallicities ($\simeq0.3\ Z_\odot$). The luminosity distribution of the CIII] emitters in our $z\simeq1-3$ sample presents a consistent picture, with stronger emission generally linked to low luminosity systems ($M_{\rm{UV}}>-19.5$) where low metallicities are more likely. We quantify the fraction of strong CIII] and CIV emitters at $z\simeq1-3$, providing a baseline for comparison against $z>6$ samples. We suggest that the first UV line detections at $z>6$ can be explained if a significant fraction of the early galaxy population is found at large sSFR ($>200$ Gyr$^{-1}$) and low metallicity ($<0.1\ Z_\odot$).

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