arXiv 1806.011912018-06astro-ph.GA

发现z = 5.72的射电星系

Discovery of a radio galaxy at z = 5.72

A. Saxena, M. Marinello, R. A. Overzier, P. N. Best, H. J. A Rottgering, K. J. Duncan, I. Prandoni, L. Pentericci, M. Magliocchetti, D. Paris, F. Cusano, F. Mar… 展开作者

A. Saxena, M. Marinello, R. A. Overzier, P. N. Best, H. J. A Rottgering, K. J. Duncan, I. Prandoni, L. Pentericci, M. Magliocchetti, D. Paris, F. Cusano, F. Marchi, H. T. Intema, G. K. Miley

备注：: 11 pages, 7 figures. Latest published version 10 October 2018
发表信息：: 2018, Monthly Notices of the Royal Astronomical Society, Volume 480, Issue 2, p.2733-2742
DOI：: 10.1093/mnras/sty1996

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摘要：

我们报告了迄今为止发现的最遥远的射电星系TGSS 1530，其红移为$z=5.72$，接近再电离时代的假定结束。射电星系是从TGSS ADR 1调查中选择的，频率为150 MHz，具有超陡的光谱指数$α^{\textrm{150 MHz}}_{\textrm{1.4 GHz}} = -1.4$和使用VLA成像在1.4 GHz获得的紧凑形态。在公开的天空调查中没有发现它的光学或红外对应物。在双子座北使用GMOS在无线电位置进行的后续光学光谱分析显示存在一条单一的发射线。我们确定这条线为莱曼α在$z=5.72$，因为它的不对称的线轮廓，在光谱中没有其他的光学/紫外线和一个高的等效宽度。TGSS 1530的Ly $α$光度为$5.7 \times 10^{42}$ erg s $^{-1}$，FWHM为$370$ km s $^{-1}$，在类似的红移下，它与“非射电”莱曼α发射体（LAEs）相当。然而，它的射电光度为$\log L_{\textrm{150 MHz}} = 29.1$ W Hz $^{-1}$，去卷积后的物理大小为$3.5$ kpc，其射电性质与$z>4$的其他已知射电星系相似。随后的$J$和$K$波段成像使用LUCI在大双筒望远镜上导致没有检测到宿主星系的$3σ$极限$J>24.4$和$K>22.4$（织女星）。$K$带限与射电星系$K-z$关系中的$z>5$一致，表明使用$M_{\textrm{stars}}< 10^{10.5}$ $M_\odot$的简单恒星种群模型的恒星质量极限。它的高红移加上相对较小的射电和Ly $α$尺寸表明，TGSS 1530可能是一个处于早期演化阶段的射电星系。

英文摘要：

We report the discovery of the most distant radio galaxy to date, TGSS1530 at a redshift of $z=5.72$ close to the presumed end of the Epoch of Reionisation. The radio galaxy was selected from the TGSS ADR1 survey at 150 MHz for having to an ultra-steep spectral index, $α^{\textrm{150 MHz}}_{\textrm{1.4 GHz}} = -1.4$ and a compact morphology obtained using VLA imaging at 1.4 GHz. No optical or infrared counterparts for it were found in publicly available sky surveys. Follow-up optical spectroscopy at the radio position using GMOS on Gemini North revealed the presence of a single emission line. We identify this line as Lyman alpha at $z=5.72$, because of its asymmetric line profile, the absence of other optical/UV lines in the spectrum and a high equivalent width. With a Ly$α$ luminosity of $5.7 \times 10^{42}$ erg s$^{-1}$ and a FWHM of $370$ km s$^{-1}$, TGSS1530 is comparable to `non-radio' Lyman alpha emitters (LAEs) at a similar redshift. However, with a radio luminosity of $\log L_{\textrm{150 MHz}} = 29.1$ W Hz$^{-1}$ and a deconvolved physical size $3.5$ kpc, its radio properties are similar to other known radio galaxies at $z>4$. Subsequent $J$ and $K$ band imaging using LUCI on the Large Binocular Telescope resulted in non-detection of the host galaxy down to $3σ$ limits of $J>24.4$ and $K>22.4$ (Vega). The $K$ band limit is consistent with $z>5$ from the $K-z$ relation for radio galaxies, suggesting stellar mass limits using simple stellar population models of $M_{\textrm{stars}}< 10^{10.5}$ $M_\odot$. Its high redshift coupled with relatively small radio and Ly$α$ sizes suggest that TGSS1530 may be a radio galaxy in an early phase of its evolution.

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