Galaxy connections

摘要

A combined millimetre- and visible-light view of a forming cluster of galaxies in the young Universe adds yet another piece to the puzzle of how today's Universe of galaxies formed and evolved. rnWhat is the evolutionary pathway of a galaxy? And how do different galaxy populations relate to one another? On page 61 of this issue, Tamura and colleagues get closer to answering these questions by showing that two apparently very dissimilar types of star-forming galaxy develop synchronously within a young cluster of galaxies seen 2 billion years after the Big Bang. rnIt is now 30 years since the advent of charge-coupled device (CCD) cameras on large optical telescopes facilitated the first meaningful searches for 'primeval' galaxies in the young Universe. These first surveys were motivated by the natural expectation that young, rapidly star-forming galaxies would be bright at ultraviolet wavelengths owing to the presence of large numbers of very hot, short-lived massive stars. In particular, it was anticipated that these galaxies would exhibit strong ultraviolet emission lines owing to the ionization and subsequent recombination of hydrogen atoms.