One of the outstanding problems of current observational cosmology is to understand the nature of sources that produced the bulk of the ionizing radiation after the Cosmic Dark Age. Direct detection of these reionization sources¹ is practically infeasible at high redshift (z) due to the steep decline of intergalactic medium transmission^2,3. However, a number of low-z analogues emitting Lyman continuum at 900 Å restframe are now detected at z < 0.4 (refs. ^4,5,6,7,8) and there are also detections in the range 2.5 < z < 3.5 (refs. ^{9,10,11,12,13,14}). Here we report the detection of Lyman continuum emission with a high escape fraction (>20%) from a low-mass clumpy galaxy at z = 1.42, in the middle of the redshift range where no detection has been made before and near the peak of the cosmic star-formation history¹⁵. The observation was made in the Hubble Extreme Deep Field¹⁶ by the wide-field Ultraviolet Imaging Telescope¹⁷ onboard AstroSat¹⁸. This detection of extreme ultraviolet radiation from a distant galaxy at a restframe wavelength of 600 Å opens up a new window to constrain the shape of the ionization spectrum. Further observations with AstroSat should substantially increase the sample of Lyman-continuum-leaking galaxies at cosmic noon.

当前的观测宇宙学的突出问题之一是要了解在宇宙黑暗时代之后产生大量电离辐射的辐射源的性质。由于银河际介质传输^2,3的急剧下降，在高红移（z）下直接检测这些电离源¹实际上是不可行的。然而，现在在z  <0.4（参考^{4、5、6、7、8}）处检测到许多在900Å静止帧发射Lyman连续谱的低z类似物（参考文献^{4、5、6、7、8}），并且在2.5 <  z  <3.5（参考文献^{9,10,11,12,13,14}）。在这里，我们报告了 在红移范围的中间，在z = 1.42处的低质量块状星系中，从低质量块状星系以高逃逸率（> 20％）检测到Lyman连续体发射的现象，在此之前和附近没有进行检测。宇宙恒星形成史¹⁵。观测是由AstroSat ¹⁸上的宽视场紫外线成像望远镜¹⁷在哈勃极端深场^16中进行的。对来自遥远星系在600Å其余帧波长处的极紫外辐射的检测打开了一个新窗口，可以限制电离光谱的形状。用AstroSat进行的进一步观察将大大增加宇宙中午出现莱曼连续渗漏星系的样本。