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Arxiv link
http://arxiv.org/abs/1305.4930
Abstract
Stellar archeology1 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⊙ yr−1). Their progenitors are likely the sub-millimeter-bright galaxies (SMGs)2 at redshifts (z) greater than 2. While SMGs’ mean molecular gas mass3 of 5×1010 M⊙ can explain the formation of typical elliptical galaxies, it is inadequate to form ellipticals4 that already have stellar masses above 2×1011 M⊙ 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⊙ yr−1. 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 ∼ 4×1011 M⊙. 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.