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


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 rapidly1,2. 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 luminous, rare objects, including mergers and quasars3,4,5, and accordingly we do not yet have a clear idea about the gas content of more normal (albeit massive) galaxies. Here we report the results of a survey of molecular gas in samples of typical massive-star-forming galaxies at mean redshifts <z> of about 1.2 and 2.3, when the Universe was respectively 40% and 24% of its current age. Our measurements reveal that distant star forming galaxies were indeed gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z = 2.3 and z = 1.2 is respectively about 44% and 34%, three to ten times higher than in today’s massive spiral galaxies6. The slow decrease between z ≈ 2 and z ≈ 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies.

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Figure 1: Integrated CO spectra.
Figure 2: CO maps in EGS 1305123.
Figure 3: High molecular gas fractions in SFGs at high z.


  1. Noeske, K. G. et al. Star formation in AEGIS field galaxies since z = 1.1: the dominance of gradually declining star formation, and the main sequence of star-forming galaxies. Astrophys. J. 660, L43–L46 (2007)

    Article  ADS  CAS  Google Scholar 

  2. Daddi, E. et al. Multiwavelength study of massive galaxies at z2. I. Star formation and galaxy growth. Astrophys. J. 670, 156–172 (2007)

    Article  ADS  CAS  Google Scholar 

  3. Greve, T. R. et al. An interferometric CO survey of luminous submillimetre galaxies. Mon. Not. R. Astron. Soc. 359, 1165–1183 (2005)

    Article  ADS  CAS  Google Scholar 

  4. Combes, F. et al. High resolution observations of a starburst at z = 0.223: resolved CO(1-0) structure. Astron. Astrophys. 460, L49–L52 (2006)

    Article  ADS  CAS  Google Scholar 

  5. Tacconi, L. J. et al. Submillimeter galaxies at z 2: evidence for major mergers and constraints on lifetimes, IMF, and CO-H2 conversion factor. Astrophys. J. 680, 246–262 (2008)

    Article  ADS  CAS  Google Scholar 

  6. Leroy, A., Bolatto, A. D., Simon, J. D. & Blitz, L. The molecular interstellar medium of dwarf galaxies on kiloparsec scales: a new survey for CO in northern, IRAS-detected dwarf galaxies. Astrophys. J. 625, 763–784 (2005)

    Article  ADS  CAS  Google Scholar 

  7. Rand, R. J. & Kulkarni, S. R. M51: molecular spiral arms, giant molecular associations and superclouds. Astrophys. J. 349, L43–L46 (1990)

    Article  ADS  Google Scholar 

  8. Rand, R. J., Kulkarni, S. R. & Rice, W. Star formation and the distribution of HI and infrared emission in M51. Astrophys. J. 390, 66–78 (1992)

    Article  ADS  CAS  Google Scholar 

  9. Förster Schreiber, N. M. et al. SINFONI integral field spectroscopy of z2 UV-selected galaxies: rotation curves and dynamical evolution. Astrophys. J. 645, 1062–1075 (2006)

    Article  ADS  Google Scholar 

  10. Förster Schreiber, N. M. et al. The SINS survey: SINFONI integral field spectroscopy of z 2 star-forming galaxies. Astrophys. J. 706, 1364–1428 (2009)

    Article  ADS  Google Scholar 

  11. Daddi, E. et al. Vigorous star formation with low efficiency in massive disk galaxies at z = 1.5. Astrophys. J. 673, L21–L24 (2008)

    Article  ADS  CAS  Google Scholar 

  12. Dannerbauer, H. et al. Low, Milky-Way-like molecular gas excitation of massive disk galaxies at z1.5. Astrophys. J. 698, L178–L182 (2009)

    Article  ADS  CAS  Google Scholar 

  13. Solomon, P. M., Rivolo, A. R., Barrett, J. & Yahil, A. Mass, luminosity, and line width relations of Galactic molecular clouds. Astrophys. J. 319, 730–741 (1987)

    Article  ADS  CAS  Google Scholar 

  14. Dickman, R. L., Snell, R. L. & Schloerb, F. P. Carbon monoxide as an extragalactic mass tracer. Astrophys. J. 309, 326–330 (1986)

    Article  ADS  CAS  Google Scholar 

  15. Bolatto, A. D., Leroy, A. K., Rosolowsky, E., Walter, F. & Blitz, L. The resolved properties of extragalactic giant molecular clouds. Astrophys. J. 686, 948–965 (2008)

    Article  ADS  CAS  Google Scholar 

  16. Baker, A. J., Tacconi, L. J., Genzel, R., Lehnert, M. D. & Lutz, D. Molecular gas in the lensed Lyman break galaxy cB58. Astrophys. J. 604, 125–140 (2004)

    Article  ADS  CAS  Google Scholar 

  17. Coppin, K. E. K. et al. A detailed study of gas and star formation in a highly magnified Lyman break galaxy at z = 3.07. Astrophys. J. 665, 936–943 (2007)

    Article  ADS  CAS  Google Scholar 

  18. Sage, L. J. Molecular gas in nearby galaxies I. CO observations of a distance-limited sample. Astron. Astrophys. 272, 123–136 (1993)

    ADS  CAS  Google Scholar 

  19. Young, J. S. & Scoville, N. Z. Molecular gas in galaxies. Annu. Rev. Astron. Astrophys. 29, 581–625 (1991)

    Article  ADS  CAS  Google Scholar 

  20. Erb, D. K. et al. Hα observations of a large sample of galaxies at z 2: implications for star formation in high-redshift galaxies. Astrophys. J. 647, 128–139 (2006)

    Article  ADS  CAS  Google Scholar 

  21. Kereš, D., Katz, N., Weinberg, D. H. & Davé, R. How do galaxies get their gas? Mon. Not. R. Astron. Soc. 363, 2–28 (2005)

    Article  ADS  Google Scholar 

  22. Ocvirk, P., Pichon, C. & Teyssier, R. Bimodal gas accretion in the Horizon-Mare Nostrum galaxy formation simulation. Mon. Not. R. Astron. Soc. 390, 1326–1338 (2008)

    ADS  CAS  Google Scholar 

  23. Dekel, A. et al. Cold streams in early massive hot haloes as the main mode of galaxy formation. Nature 457, 451–454 (2009)

    Article  ADS  CAS  Google Scholar 

  24. White, S. D. M. & Rees, M. J. Core condensation in heavy halos — A two-stage theory for galaxy formation and clustering. Mon. Not. R. Astron. Soc. 183, 341–358 (1978)

    Article  ADS  Google Scholar 

  25. Birnboim, Y. & Dekel, A. Virial shocks in galactic haloes? Mon. Not. R. Astron. Soc. 345, 349–364 (2003)

    Article  ADS  Google Scholar 

  26. Kennicutt, R. C. The global Schmidt Law in star-forming galaxies. Astrophys. J. 498, 541–552 (1998)

    Article  ADS  CAS  Google Scholar 

  27. Chabrier, G. Galactic stellar and substellar initial mass function. Publ. Astron. Soc. Pacif. 115, 763–795 (2003)

    Article  ADS  Google Scholar 

  28. Davis, M. et al. The All-Wavelength Extended Groth Strip International Survey (AEGIS) data sets. Astrophys. J. 660, L1–L6 (2007)

    Article  ADS  Google Scholar 

  29. Steidel, C. C. et al. A survey of star-forming galaxies in the 1.4<z< 2.5 redshift desert: overview. Astrophys. J. 604, 534–550 (2004)

    Article  ADS  CAS  Google Scholar 

  30. Cox, P. (ed.) IRAM Annual Report 2006 (IRAM, Grenoble, 2006); IRAM Annual Report 2007 (IRAM, Grenoble, 2007); available at 〈

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This work is based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). We thank B. Lazareff and the IRAM staff for their work in developing the new PdBI receiver systems, which made these technically difficult observations feasible. We are grateful to J. Blaizot, L.-M. Dansac, R. Davé, D. Kereŝ, P. Ocvirk, C. Pichon and R. Teyssier for communicating unpublished results of their simulations and for discussions. A.B. and T.N. thank the Cluster of Excellence "Origin and Structure of the Universe" for support. M.C.C. is a Spitzer Fellow; A.B. is a Max Planck Fellow.

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Correspondence to L. J. Tacconi.

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Tacconi, L., Genzel, R., Neri, R. et al. High molecular gas fractions in normal massive star-forming galaxies in the young Universe. Nature 463, 781–784 (2010).

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