The intense starburst HDF 850.1 in a galaxy overdensity at z ≈ 5.2 in the Hubble Deep Field

摘要

The Hubble Deep Field provides one of the deepest multiwave-length views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time. An early map of the Hubble Deep Field at a wavelength of 850 micrometres, which is sensitive to dust emission powered by star formation, revealed the brightest source in the field, dubbed HDF 850.1 (ref. 2). For more than a decade, and despite significant efforts, no counterpart was found at shorter wavelengths, and it was not possible to determine its redshift, size or mass. Here we report a redshift of z = 5.183 for HDF 850.1, from a millimetre-wave molecular line scan. This places HDF 850.1 in a galaxy overdensity at z≈ 5.2, corresponding to a cosmic age of only 1.1 billion years after the Big Bang. This redshift is significantly higher than earlier estimates and higher than those of most of the hundreds of submillimetre-bright galaxies identified so far. The source has a star-formation rate of 850 solar masses per year and is spatially resolved on scales of 5 kiloparsecs, with an implied dynamical mass of about 1.3 × 10~(11) solar masses, a significant fraction of which is present in the form of molecular gas. Despite our accurate determination of redshift and position, a counterpart emitting starlight remains elusive.%在Hubble Deep Field所看到的遥远宇宙中最遥rn远的亚毫米射电源(被称为HDF 850.1)，已被rn证明像谜一般，尽管人们进行了密集的搜索，rn但它还是难以在可见光和近红外范围内被检测rn到。由于没有在较短波长发现一个对应的光rn源，所以一直没有可能直接估计该光源的红rn移、大小或质量。现在，通过“毫米波分子线rn扫描”，HDF 850.1的红移已被确定。它的红rn移值为z≈5.2，要比人们所预料的高很多，相rn当于其宇宙年龄仅为“大爆炸”后11亿年。利rn用这些新数据所做的计算表明，其年恒星形成rn速度高达850个太阳质量，质量高达1.3×1O～(11)rn个太阳质量。但迄今仍未发现存在一个发射星rn光的对应体的迹象。