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Witnessing the Birth of the Red Sequence: ALMA High-resolution Imaging of [C II] and Dust in Two Interacting Ultra-red Starbursts at z = 4.425

I. Oteo, R. J. Ivison, L. Dunne, I. Smail, A. M. Swinbank, Z-Y. Zhang, A. Lewis, S. J. Maddox, D. A. Riechers, S. Serjeant, P. van der Werf, A. D. Biggs, M. N. Bremer, P. Cigan, D. L. Clements, A. Cooray, H. Dannerbauer, S. Eales, E. Ibar, H. Messias, M. J. Michałowski, I. Pérez-Fournon, E. van Kampen

Abstract
Exploiting the sensitivity and spatial resolution of the Atacama Large Millimeter/submillimeter Array, we have studied the morphology and the physical scale of the interstellar medium—both gas and dust—in SGP 38326, an unlensed pair of interacting starbursts at z = 4.425. SGP 38326 is the most luminous star bursting system known at z > 4, with a total IR luminosity of LIR ~ 2.5 × 1013 L and a star formation rate of ~4500 M yr-1. SGP 38326 also contains a molecular gas reservoir among the most massive yet found in the early universe, and it is the likely progenitor of a massive, red-and-dead elliptical galaxy at z ~ 3. Probing scales of ~0".1 or ~800 pc we find that the smooth distribution of the continuum emission from cool dust grains contrasts with the more irregular morphology of the gas, as traced by the [C ii] fine structure emission. The gas is also extended over larger physical scales than the dust. The velocity information provided by the resolved [C ii] emission reveals that the dynamics of the two interacting components of SGP 38326 are each compatible with disk-like, ordered rotation, but also reveals an ISM which is turbulent and unstable. Our observations support a scenario where at least a subset of the most distant extreme starbursts are highly dissipative mergers of gas-rich galaxies.

Keywords
galaxies: high-redshift, galaxies: ISM, galaxies: starburst, submillimeter: galaxies

The Astrophysical Journal
Volume 827, Number 1
2016 August

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia