We report the discovery of J0121+0025, an extremely luminous and young star-forming galaxy (MUV = −24.11, log[$L_{\rm Ly \alpha } / \rm erg~s^{-1}] = 43.8$) at z = 3.244 showing copious Lyman continuum (LyC) leakage ($f_{\rm esc, abs} \approx 40{{\ \rm per\ cent}}$). High signal-to-noise ratio rest-frame UV spectroscopy with the Gran Telescopio Canarias reveals a high significance (7.9σ) emission below the Lyman limit (<912 Å), with a flux density level f900 = 0.78 ± 0.10μJy, and strong P-Cygni in wind lines of O vi 1033 Å, N v 1240 Å, and C iv 1550 Å that are indicative of a young age of the starburst (<10 Myr). The spectrum is rich in stellar photospheric features, for which a significant contribution of an AGN at these wavelengths is ruled out. Low-ionization interstellar medium (ISM) absorption lines are also detected, but are weak ($EW_{0} \rm \simeq 1$ Å) and show large residual intensities, suggesting a clumpy geometry of the gas with a non-unity covering fraction or a highly ionized ISM. The contribution of a foreground and AGN contamination to the LyC signal is unlikely. Deep optical to Spitzer/IRAC 4.5 μm imaging show that the spectral energy distribution of J0121+0025 is dominated by the emission of the young starburst, with log($M_{\star }^{\rm burst}/M_{\odot }) = 9.9\pm 0.1$ and $\rm SFR = 981\pm 232$ M⊙ yr−1. J0121+0025 is the most powerful LyC emitter known among the star-forming galaxy population. The discovery of such luminous and young starburst leaking LyC radiation suggests that a significant fraction of LyC photons can escape in sources with a wide range of UV luminosities and are not restricted to the faintest ones as previously thought. These findings might shed further light on the role of luminous starbursts to the cosmic reionization.

中文翻译：

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紫外线最亮的莱曼连续体发射恒星形成星系

我们报告了 J0121+0025 的发现，这是一个极其明亮的年轻恒星形成星系 (MUV = -24.11, log[$L_{\rm Ly \alpha } / \rm erg~s^{-1}] = 43.8$ ) 在 z = 3.244 处显示大量莱曼连续谱 (LyC) 泄漏（$f_{\rm esc, abs} \约 40{{\ \rm per\ cent}}$）。使用 Gran Telescopio Canarias 的高信噪比静止帧紫外光谱揭示了低于莱曼极限 (<912 Å) 的高显着性 (7.9σ) 发射，通量密度水平 f900 = 0.78 ± 0.10μJy，并且O vi 1033 Å、N v 1240 Å 和 C iv 1550 Å 的风线中强烈的天鹅座 P-表明星暴的年轻年龄（<10 Myr）。该光谱具有丰富的恒星光球特征，因此排除了活动星系核在这些波长上的重要贡献。还检测到低电离星际介质 (ISM) 吸收线，但很弱（$EW_{0} \rm \simeq 1$ Å）并显示出较大的残余强度，表明气体的团块几何形状具有非统一的覆盖分数或高度电离的 ISM。前景和 AGN 污染对 LyC 信号的贡献不太可能。Spitzer/IRAC 4.5 μm 深度光学成像表明 J0121+0025 的光谱能量分布主要由年轻星暴的发射决定，log($M_{\star }^{\rm burst}/M_{\odot } ) = 9.9\pm 0.1$ 和 $\rm SFR = 981\pm 232$ M⊙ yr−1。J0121+0025 是恒星形成星系群中已知的最强大的 LyC 发射器。这种发光和年轻的星暴泄漏 LyC 辐射的发现表明，很大一部分 LyC 光子可以在具有广泛紫外光度的源中逸出，并且不限于以前认为的最微弱的光子。