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arXiv 2310.08441astro-ph.GA
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低红移极贫金属致密恒星形成星系中的Ly-alpha发射

Ly-alpha emission in low-redshift most metal-deficient compact star-forming galaxies

Y. I. Izotov, T. X. Thuan, N. G. Guseva, D. Schaerer, G. Worseck, A. Verhamme

AI总结:

本研究通过哈勃望远镜观测9个低红移极贫金属致密恒星形成星系,发现其均为Ly-alpha发射体,明确了Ly-alpha逃逸分数的相关特征,提出间接估算电离辐射的方法,证实这类星系可作为宇宙再电离时期的近邻研究参照。

摘要:

我们利用哈勃空间望远镜搭载的宇宙起源光谱仪(Cosmic Origins Spectrograph),对9个极贫金属致密恒星形成星系开展了观测,这些星系的氧丰度为12+log(O/H)=6.97-7.23,红移z=0.02811-0.13320,恒星质量M*<10^7太阳质量(Msun)。本研究旨在探究这些极端贫金属天体的Ly-alpha发射特性。研究发现,这9个星系均为Ly-alpha发射体(LAEs)。我们对大样本LAEs(包括本次研究的最低金属丰度星系及文献中的其他天体)的Ly-alpha逃逸分数fesc(Ly-alpha)与其他特征的关联进行了检验,涉及的特征包括紫外绝对星等、氧丰度、O32比值、恒星质量、Ly-alpha光度与等值宽度EW(Ly-alpha)、电离光子产生效率,以及Ly-alpha谱线双峰之间的速度间隔Vsep。结果显示,fesc(Ly-alpha)与EW(Ly-alpha)、Vsep这两个特征存在相对紧密的相关性,而fesc(Ly-alpha)与氧丰度之间未发现相关性。我们还发现Ly-alpha逃逸分数与LyC逃逸分数之间存在相对紧密的关联,并提出当无法直接测量LyC发射时,可利用这一关联间接估算LAEs的逃逸电离辐射。研究表明,低红移LAEs的整体性质与z>6的星系非常相似,因此它们是研究宇宙再电离时期物理过程的理想近邻参照天体。

英文摘要:

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of nine most metal-deficient compact star-forming galaxies with oxygen abundances 12+log(O/H)=6.97-7.23, redshifts z=0.02811-0.13320, and stellar masses M*<10^7Msun. We aim to study the properties of Ly-alpha emission in these extremely metal-deficient objects. We find that all nine galaxies are Ly-alpha emitters (LAEs). We examine various relations between the Ly-alpha escape fraction fesc(Ly-alpha) and other characteristics - such as absolute UV magnitude, oxygen abundance, O32 ratio, stellar mass, Lyman-alpha luminosity and equivalent width EW(Ly-alpha), ionizing photon production efficiency and velocity separation Vsep between the two peaks of the Ly-alpha profile - of a large sample of LAEs, including our lowest-metallicity galaxies and other objects from the literature. We find a relatively tight correlation between fesc(Ly-alpha) and two characteristics, EW(Ly-alpha) and Vsep, whereas no correlation is found between fesc(Ly-alpha) and the oxygen abundance. We also find a relatively tight relation between the Ly-alpha and LyC escape fractions. We propose to use the latter relation to estimate indirectly the escaping ionizing radiation in LAEs, when direct measurements of LyC emission are not possible. We show that the global properties of low-z LAEs are very similar to those of z>6 galaxies. They are thus ideal local proxies for studying physical processes during the epoch of reionization of the Universe.

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