R. J. Ivison, A. M. Swinbank, Ian Smail, A. I. Harris, R. S. Bussmann, A. Cooray, P. Cox, Hai Fu, A. Kovacs, M. Krips, D. Narayanan, M. Negrello, R. Neri, J. Penarrubia, J. Richard, D. A. Riechers, K. Rowlands, J. G. Staguhn, T. A. Targett, S. Amber, A. J. Baker, N. Bourne, F. Bertoldi, M. Bremer, J. A. Calanog, D. L. Clements, H. Dannerbauer, A. Dariush, G. De Zotti, L. Dunne, S. A. Eales, D. Farrah, S. Fleuren, A. Franceschini, J. E. Geach, R. D. George, J. C. Helly, R. Hopwood, E. Ibar, M. J. Jarvis, J. -P. Kneib, S. Maddox, A. Omont, D. Scott, S. Serjeant, M. W. L. Smith, M. A. Thompson, E. Valiante, I. Valtchanov, J. Vieira, P. van der Werf
Exploiting the relationship between CO luminosity and line width determined for fainter starbursts, we identify and remove lensed sources from the widest Herschel extragalactic imaging survey to yield a sample of intrinsically luminous galaxies. Panchromatic observations of the best candidate HyLIRG then led to the discovery of at least four luminous galaxies across a ~100-kpc region at z=2.41. Our technique separates HyLIRGs from the more numerous, strongly lensed population, and can also pinpoint clusters of starbursting proto-ellipticals. Via sub-arcsecond interferometric imaging we have measured accurate gas and star-formation surface densities. The two brightest galaxies span ~3 kpc FWHM in submm/radio continuum and CO J=4-3, and double that in CO J=1-0. The broad CO line is due partly to the multitude of constituent galaxies and partly to large rotational velocities in two counter-rotating gas disks -- a scenario predicted to lead to the most intense starbursts, which will therefore come in pairs. The disks have M(dyn) of several x 10^11 Msun, and gas fractions of ~40%. Velocity dispersions are modest so the disks are unstable, potentially on scales commensurate with their radii: these galaxies are undergoing extreme bursts of star formation, not confined to their nuclei, at close to the Eddington limit. Their specific star-formation rates place them ~>5x above the main sequence, which supposedly comprises large gas disks like these. Their high star-formation efficiencies are difficult to reconcile with a simple volumetric star-formation law. N-body and dark matter simulations suggest this system is the progenitor of a B(inary)-type ~10^14.6-Msun cluster.
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http://arxiv.org/abs/1302.4436
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