A dusty, normal galaxy in the epoch of reionization

摘要

Candidates for the modest galaxies that formed most of the stars in the early Universe, at redshifts z ＞ 7, have been found in large numbers with extremely deep restframe-ultraviolet imaging. But it has proved difficult for existing spectrographs to characterize them using their ultraviolet light. The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and Metals. So far, however, the most distant galaxy discovered via its ultraviolet emission and subsequently detected in dust emission is only at z = 3.2 (ref. 5), and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at z ≥ 7. Here we report thermal dust emission from an archetypal early Universe star-forming galaxy, Al689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be z = 7.5 ± 0.2 from a spectroscopic detection of the Lyman-α break. A1689-zD1 is representative of the star-forming population during the epoch of reionization, with a total star-formation rate of about 12 solar masses per year. The galaxy is highly evolved: it has a large stellar mass and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at z ＞ 7.%早期宇宙中星系的红外和毫米波观测测量结果将可显示它们的详细特性，但此前一直没有关于富含金属的尘埃星系(大多数恒星从中形成的典型星系)的这种数据。Darach Watson等人在本文中发表了对一个原始成星星系(高红移星系A1689-ZD1)的红外光谱和毫米波连续观测结果，这些数据使研究人员能够对该星系的尘埃质量、总成星速度和尘埃—气体比进行计算。他们计算出其红移值为z = 7.5±0.2,总成星速度约为每年12个太阳质量。该星系处于高度演变状态，具有很大恒星质量，其尘埃—气体比接近银河系。