Hai Fu, Asantha Cooray, C. Feruglio, R. J. Ivison, D. A. Riechers, M. Gurwell, R. S. Bussmann, A. I. Harris, B. Altieri, H. Aussel, A. J. Baker, J. Bock, M. Boylan-Kolchin, C. Bridge, J. A. Calanog, C. M. Casey, A. Cava, S. C. Chapman, D. L. Clements, A. Conley, P. Cox, D. Farrah, D. Frayer, R. Hopwood, J. Jia, G. Magdis, G. Marsden, P. Martinez-Navajas, M. Negrello, R. Neri, S. J. Oliver, A. Omont, M. J. Page, I. Perez-Fournon, B. Schulz, D. Scott, A. Smith, M. Vaccari, I. Valtchanov, J. D. Vieira, M. Viero, L. Wang, J. L. Wardlow, M. Zemcov
Stellar archeology shows that massive elliptical galaxies today formed rapidly about ten billion years ago with star formation rates above several hundreds solar masses per year (M_sun/yr). Their progenitors are likely the sub-millimeter-bright galaxies (SMGs) at redshifts (z) greater than 2. While SMGs' mean molecular gas mass of 5x10^10 M_sun can explain the formation of typical elliptical galaxies, it is inadequate to form ellipticals that already have stellar masses above 2x10^11 M_sun at z ~ 2. Here we report multi-wavelength high-resolution observations of a rare merger of two massive SMGs at z = 2.3. The system is currently forming stars at a tremendous rate of 2,000 M_sun/yr. With a star formation efficiency an order-of-magnitude greater than that of normal galaxies, it will quench the star formation by exhausting the gas reservoir in only ~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 ~4x10^11 M_sun. Our observations show that gas-rich major galaxy mergers, concurrent with intense star formation, can form the most massive elliptical galaxies by z ~ 1.5.
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http://arxiv.org/abs/1305.4930
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