A hoard of previously missing galaxies from the early universe has now been found. Dating back to the first two billion years of the cosmos, these galaxies represent a key missing link to some of the most massive galaxies seen today.
Tao Wang at the University of Tokyo in Japan and his colleagues discovered 39 massive star-forming galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. We have found galaxies in the early universe that are more massive than these, with star formation rates of more than 1000 solar masses per year. But these newly unearthed galaxies still have impressive star formation rates of about 200 solar masses per year, and represent a class rarely seen before.
鈥淭he unique property of these galaxies is that they are really faint in the ultraviolet to optical light,鈥� says Wang. 鈥淭hat鈥檚 why they are invisible from the Hubble Space Telescope, which is the usual way to find these galaxies in the early universe.鈥�
Advertisement
Most massive galaxies today聽evolved from those in the early universe, but until now, astronomers had been unable to find enough massive galaxies in the early universe to account for the large number of massive galaxies five to 10 times the mass of the Milky Way we see in the local universe today.
The reason, as revealed by Wang and his colleagues, isn鈥檛 that they aren鈥檛 there but that the progenitors of these galaxies are so dusty that they are invisible in optical light. We can only see them in radio wavelengths, as observed by ALMA.
While a couple of these galaxies have been found before, this is the first time such a large population has been tracked down. And it poses some questions about our early universe, namely, how were so many large galaxies able to form when it was so young? 鈥淭he next step will be to figure out the missing physics in producing so many massive galaxies that early,鈥� says Wang.
Nature
