Witnessing the birth of the red sequence: ALMA high-resolution imaging of [CII] and dust in two interacting ultra-red starbursts at z = 4.425

Oteo, I.; Ivison, R. J.; Dunne, L.; Smail, I.; Swinbank, A. M.; Zhang, Z-Y.; Lewis, A.; Maddox, S.; Riechers, D.; Serjeant, S.; Werf, P. Van der; Biggs, A. D.; Bremer, M.; Cigan, P.; Clements, D. L.; Cooray, A.; Dannerbauer, H.; Eales, S.; Ibar, E.; Messias, H.; Michałowski, M. J.; Pérez-Fournon, I. and Kampen, E. van (2016). Witnessing the birth of the red sequence: ALMA high-resolution imaging of [CII] and dust in two interacting ultra-red starbursts at z = 4.425. The Astrophysical Journal, 827(1), article no. 34.

DOI: https://doi.org/10.3847/0004-637X/827/1/34

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 L IR ~ 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 [CII] fine structure emission. The gas is also extended over larger physical scales than the dust. The velocity information provided by the resolved [CII] 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.

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