Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile.
Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4059, Valparaíso, Chile.
Nature. 2018 Feb 22;554(7693):493-496. doi: 10.1038/nature25436. Epub 2018 Jan 31.
Every star-forming galaxy has a halo of metal-enriched gas that extends out to at least 100 kiloparsecs, as revealed by the absorption lines that this gas imprints on the spectra of background quasars. However, quasars are sparse and typically probe only one narrow beam of emission through the intervening galaxy. Close quasar pairs and gravitationally lensed quasars have been used to circumvent this inherently one-dimensional technique, but these objects are rare and the structure of the circumgalactic medium remains poorly constrained. As a result, our understanding of the physical processes that drive the recycling of baryons across the lifetime of a galaxy is limited. Here we report integral-field (tomographic) spectroscopy of an extended background source-a bright, giant gravitational arc. We can thus coherently map the spatial and kinematic distribution of Mg ɪɪ absorption-a standard tracer of enriched gas-in an intervening galaxy system at redshift 0.98 (around 8 billion years ago). Our gravitational-arc tomography unveils a clumpy medium in which the absorption strength decreases with increasing distance from the galaxy system, in good agreement with results for quasars. Furthermore, we find strong evidence that the gas is not distributed isotropically. Interestingly, we detect little kinematic variation over a projected area of approximately 600 square kiloparsecs, with all line-of-sight velocities confined to within a few tens of kilometres per second of each other. These results suggest that the detected absorption originates from entrained recycled material, rather than in a galactic outflow.
每个形成恒星的星系都有一个富含金属的气体晕，其延伸范围至少达到 100 千秒差距，这是由该气体在背景类星体光谱中产生的吸收线揭示的。然而，类星体很稀疏，通常只能通过星系间的一个狭窄射束来探测。紧密的类星对和引力透镜类星体已被用于规避这种固有一维技术，但这些物体很少见，星系晕外介质的结构仍然受到很大限制。因此，我们对驱动星系寿命内重子循环的物理过程的理解是有限的。在这里，我们报告了对一个扩展背景源-一个明亮的巨大引力弧-的积分场（层析）光谱。因此，我们可以在一个红移为 0.98（约 80 亿年前）的星系系统中相干地绘制出富含镁的吸收（一种标准示踪气体）的空间和运动分布。我们的引力弧层析术揭示了一个团块介质，其中吸收强度随着与星系系统的距离增加而降低，这与类星体的结果非常吻合。此外，我们有强有力的证据表明，气体不是各向同性分布的。有趣的是，我们在大约 600 千秒差距的投影面积上检测到很少的运动变化，所有视线速度彼此之间的差异都在几十公里/秒以内。这些结果表明，检测到的吸收来自于被卷入的再循环物质，而不是来自星系外流。
