European Southern Observatory: Astronomers have long known that in many surveys of the very distant Universe, a large fraction of the total intrinsic light was not being observed. Now, thanks to an extremely deep survey using two of the four giant 8.2-metre telescopes that make up ESO's Very Large Telescope (VLT) and a unique custom-built filter, astronomers have determined that a large fraction of galaxies whose light took 10 billion years to reach us have gone undiscovered. The survey also helped uncover some of the faintest galaxies ever found at this early stage of the Universe.Astronomers frequently use the strong, characteristic 'fingerprint' of light emitted by hydrogen known as the Lyman-alpha line, to probe the amount of stars formed in the very distant Universe... 'Astronomers always knew they were missing some fraction of the galaxies in Lyman-alpha surveys,' explains Matthew Hayes, the lead author of the paper, published in Nature, 'but for the first time we now have a measurement. The number of missed galaxies is substantial.'... Many galaxies, a proportion as high as 90%, go unseen by these surveys...
Different observational methods, targeting the light emitted at different wavelengths, will always lead to a view of the Universe that is only partially complete. The results of this survey issue a stark warning for cosmologists, as the strong Lyman-alpha signature becomes increasingly relied upon in examining the very first galaxies to form in the history of the Universe. 'Now that we know how much light we've been missing, we can start to create far more accurate representations of the cosmos, understanding better how quickly stars have formed at different times in the life of the Universe,' says co-author Miguel Mas-Hesse.
