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arXiv 2312.04151astro-ph.GA
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JWST NIRSpec对一个经MUSE确认的z=5.66强Lyα发射体的Lyα未探测

The Ly$α$ non-detection by JWST NIRSpec of a strong Ly$α$ emitter at $z=5.66$ confirmed by MUSE

Haochen Jiang, Xin Wang, Cheng Cheng, Xu Kong, QianQiao Zhou, Xiao-Lei Meng, Xianlong He, Tucker Jones, Kristan Boyett

AI总结:

研究通过MUSE确认但JWST NIRSpec未探测到Lyα的z=5.66星系,结合NIRCam空间分辨分析揭示狭缝位置、中性氢散射与尘埃消光可导致逃逸分数严重低估。

摘要:

在红移高于5的星系中探测Lyman-α(Lyα)发射,对于约束宇宙再电离时间线至关重要,但此类探测通常基于狭缝光谱。本文通过介绍一个位于z=5.66、名为A2744-z6Lya的星系,研究狭缝位置对Lyα逃逸分数(f_esc^Lyα)估计所造成的显著偏差;在该星系中,深度JWST NIRSpec棱镜光谱完全遗漏了MUSE数据所探测到的强Lyα发射。A2744-z6Lya呈现出显著的紫外连续谱,具有极陡的β=-2.574_{-0.008}^{+0.008}光谱斜率,恒星质量约为10^8.82 M_⊙,恒星形成率约为8.35 M_⊙ yr^-1,气相金属丰度为12+log(O/H)约7.88。MUSE光谱测得其Lyα的观测流量和静止系等值宽度分别为1.2×10^-16 erg s^-1 cm^-2和75 Å,对应f_esc^Lyα=78±4%。然而,JWST NIRSpec对其Lyα的未探测给出5σ上限<13%,与MUSE所得结果形成鲜明对比。为探究这一偏差的原因,我们利用JWST NIRCam成像数据对A2744-z6Lya开展空间分辨的恒星族群分析,构建SFR、尘埃消光和中性氢柱密度的二维图。我们发现,狭缝区域内Lyα的缺失可能同时源于中性氢的共振散射效应和尘埃消光。通过详细分析一个极端案例,本工作强调了由狭缝光谱推断f_esc^Lyα时的重要注意事项,尤其是在使用JWST多路复用NIRSpec微快门组件时。

英文摘要:

The detections of Lyman-$α$ ($\rm Lyα$) emission in galaxies with redshifts above 5 are of utmost importance for constraining the cosmic reionization timeline, yet such detections are usually based on slit spectroscopy. Here we investigate the significant bias induced by slit placement on the estimate of $\rm Lyα$ escape fraction ( $f_{\rm esc}^{\mathrm{Lyα}}$), by presenting a galaxy (dubbed A2744-z6Lya) at $z=5.66$ where its deep JWST NIRSpec prism spectroscopy completely misses the strong $\rm Lyα$ emission detected in the MUSE data. A2744-z6Lya exhibits a pronounced UV continuum with an extremely steep spectral slope of $β=-2.574_{-0.008}^{+0.008}$, and it has a stellar mass of $\mathrm{\sim10^{8.82}~M_\odot}$, a star-formation rate of $\mathrm{\sim8.35~M_\odot yr^{-1}}$ and gas-phase metallicity of $\mathrm{12+log\,(O/H)\sim7.88}$. The observed flux and rest-frame equivalent width of its Ly$α$ from MUSE spectroscopy are $1.2\times \rm 10^{-16} erg~s^{-1}cm^{-2}$ and 75Å, equivalent to $f_{\rm esc}^{\mathrm{Lyα}}=78\pm4 \%$. However, its Ly$α$ non-detection from JWST NIRSpec gives a 5-$σ$ upper limit of $<13 \%$, in stark contrast to that derived from MUSE. To explore the reasons for this bias, we perform spatially resolved stellar population analysis of A2744-z6Lya using the JWST NIRCam imaging data to construct 2-dimensional maps of SFR, dust extinction and neutral hydrogen column density. We find that the absence of Ly$α$ in the slit regions probably stems from both the resonance scattering effect of neutral hydrogen and dust extinction. Through analyzing an extreme case in detail, this work highlights the important caveat of inferring $f_{\rm esc}^{\mathrm{Lyα}}$ from slit spectroscopy, particularly when using the JWST multiplexed NIRSpec microshutter assembly.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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