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arXiv 2301.11264astro-ph.GA
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SDSS中CASSOWARY引力透镜星系的光谱学:在$z=1.42$上一个极亮再电离时代类似物的特征

Spectroscopy of CASSOWARY gravitationally-lensed galaxies in SDSS: characterisation of an extremely bright reionization-era analog at $z=1.42$

Ramesh Mainali, Daniel P. Stark, Tucker Jones, Richard S. Ellis, Yashar D. Hezaveh, Jane R. Rigby

摘要:

我们提出了新的观测十六个明亮的($r=19-21$)引力透镜星系在$z\simeq 1-3$从CASSOWARY调查选择。我们的样本中包括$z=1.42$星系CSWA-141,它是已知的最亮的再电离时代类似物之一,具有高红移(g=20.5),具有大的sSFR(31.2 Gyr $^{-1}$)和[OIII]+H $β$等效宽度(EW $_{\rm{[OIII]+Hβ}}$ =730 Gyr),几乎与$z\simeq 7-8$预期的平均值相同。在本文中,我们调查了我们的样品中的静止框架UV星云线发射,目的是了解调节强CIII]发射的因素。尽管我们的样品中的大多数源显示出弱的UV线发射,但我们发现CSWA-141的光谱中的升高的CIII](EW $_{\rm{CIII]}}$ =4.6 $\pm1.9$ ~ X)以及检测到其他突出的发射线(OIII]、Si III]、Fe II、$^\star$、Mg II)。我们比较了具有强和弱CIII]发射的高红移星系的静止光学线特性,发现具有最强紫外线发射的系统倾向于具有年轻的恒星种群和中等金属贫乏和高度电离的星云气体,与低和高红移的趋势一致。CSWA-141的亮度使人们能够详细研究$z>6$上常见的极端发射线星系。我们发现,由CIII]双峰追踪的气体可能比由[OII]和[SII]追踪的气体探测到更高的密度。光谱解析镁II发射线和几个低电离吸收线的特征表明,年轻恒星周围的中性气体可能是光学薄,可能有助于电离辐射的逃逸。

英文摘要:

We present new observations of sixteen bright ($r=19-21$) gravitationally lensed galaxies at $z\simeq 1-3$ selected from the CASSOWARY survey. Included in our sample is the $z=1.42$ galaxy CSWA-141, one of the brightest known reionization-era analogs at high redshift (g=20.5), with a large sSFR (31.2 Gyr$^{-1}$) and an [OIII]+H$β$ equivalent width (EW$_{\rm{[OIII]+Hβ}}$=730~Å) that is nearly identical to the average value expected at $z\simeq 7-8$. In this paper, we investigate the rest-frame UV nebular line emission in our sample with the goal of understanding the factors that regulate strong CIII] emission. Whereas most of the sources in our sample show weak UV line emission, we find elevated CIII] in the spectrum of CSWA-141 (EW$_{\rm{CIII]}}$=4.6$\pm1.9$~Å) together with detections of other prominent emission lines (OIII], Si III], Fe II$^\star$, Mg II). We compare the rest-optical line properties of high redshift galaxies with strong and weak CIII] emission, and find that systems with the strongest UV line emission tend to have young stellar populations and nebular gas that is moderately metal-poor and highly ionized, consistent with trends seen at low and high redshift. The brightness of CSWA-141 enables detailed investigation of the extreme emission line galaxies which become common at $z>6$. We find that gas traced by the CIII] doublet likely probes higher densities than that traced by [OII] and [SII]. Characterisation of the spectrally resolved Mg II emission line and several low ionization absorption lines suggests neutral gas around the young stars is likely optically thin, potentially facilitating the escape of ionizing radiation.

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