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Published June 20, 2013 | Supplemental Material + Submitted
Journal Article Open

The rapid assembly of an elliptical galaxy of 400 billion solar masses at a redshift of 2.3


Stellar archaeology shows that massive elliptical galaxies formed rapidly about ten billion years ago with star-formation rates of above several hundred solar masses per year. Their progenitors are probably the submillimetre bright galaxies at redshifts z greater than 2. Although the mean molecular gas mass (5 × 10^(10) solar masses) of the submillimetre bright galaxies can explain the formation of typical elliptical galaxies, it is inadequate to form elliptical galaxies4 that already have stellar masses above 2 × 10^(11) solar masses at z ≈ 2. Here we report multi-wavelength high-resolution observations of a rare merger of two massive submillimetre bright galaxies at z = 2.3. The system is seen to be forming stars at a rate of 2,000 solar masses per year. The star-formation efficiency is an order of magnitude greater than that of normal galaxies, so the gas reservoir will be exhausted and star formation will be quenched in only around 200 million years. At a projected separation of 19  kiloparsecs, the two massive starbursts are about to merge and form a passive elliptical galaxy with a stellar mass of about 4 × 10^(11) solar masses. We conclude that gas-rich major galaxy mergers with intense star formation can form the most massive elliptical galaxies by z ≈ 1.5.

Additional Information

© 2013 Nature Publishing Group, a division of Macmillan Publishers Limited. Received 15 February; accepted 12 April 2013. Published online 22 May. Corrected online 19 June 2013--The x and y axis labels of Fig. 1b were corrected. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. This research has made use of data from the HerMES project (http://hermes.sussex.ac.uk/). HerMES is a Herschel Key Programme using Guaranteed Time from the SPIRE instrument team, ESAC scientists and a mission scientist. SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including the University of Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, the University of Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, the University of Sussex (UK); and Caltech/JPL, IPAC and the University of Colorado (USA). This development has been supported by the following national funding agencies: CSA (Canada); NAOC (China); CEA, CNES and CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC (UK); and NASA (USA). The data presented in this paper will be released through the HeDaM Database in Marseille at http://hedam.oamp.fr/HerMES. Author Contributions: H.F. and A.C. wrote the manuscript and led the project. C.F., R.J.I., D.A.R., M.G., R.S.B. and A.I.H. contributed significantly to the taking and analysis of the follow-up data with various instruments. All other co-authors of this paper contributed extensively and equally by their varied contributions to the HerMES project, planning of HerMES observations, analysis of HerMES data, and by commenting on this manuscript as part of an internal review process.

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