High molecular gas fractions in normal massive star-forming galaxies in the young Universe

  title={High molecular gas fractions in normal massive star-forming galaxies in the young Universe},
  author={Linda J. Tacconi and Reinhard Genzel and Roberto Neri and Pierre Cox and Michael C. Cooper and Kristen Leah Shapiro and Alberto D. Bolatto and Nicolas Bouch{\'e} and Fr{\'e}d{\'e}ric Bournaud and Andreas Burkert and Françoise Combes and Julia M. Comerford and Marc Davis and Natascha M. Forster Schreiber and Santiago Garc{\'i}a-Burillo and Javier Graci{\'a}-Carpio and Dieter Lutz and Thorsten Naab and Alain Omont and Alice E. Shapley and Amiel Sternberg and Benjamin J. Weiner},
Stars form from cold molecular interstellar gas. As this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more molecular-gas rich. Molecular gas observations in the distant Universe have so far largely been restricted to very… 
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