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ALMA resolves turbulent, rotating [CII] emission in a young starburst galaxy at z = 4.8.

De Breuck, C. and Williams, R.J. and Swinbank, M. and Caselli, P. and Coppin, K. and Davis, T.A. and Maiolino, R. and Nagao, T. and Smail, I. and Walter, F. and Weiß, A. and Zwaan, M.A. (2014) 'ALMA resolves turbulent, rotating [CII] emission in a young starburst galaxy at z = 4.8.', Astronomy and astrophysics., 565 . A59.


We present spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) [Cii] observations of the z = 4.7555 submillimetre galaxy, ALESS 73.1. Our 0.̋5 FWHM map resolves the [Cii] emitting gas which is centred close to the active galactic nucleus (AGN). The gas kinematics are dominated by rotation but with high turbulence, vrot/σint ~ 3.1, and a Toomre Q parameter <1 throughout the disk. By fitting three independent thin rotating disk models to our data, we derive a total dynamical mass of 3 ± 2 × 1010 M⊙. This is close to the molecular gas mass derived from previous CO(2-1) observations, and implies a CO to H2 conversion factor αCO < 2.3 M⊙ (K km s-1 pc2)-1. The mass budget also constrains the stellar mass to <3.1 × 1010 M⊙, and entails a gas fraction of fgas ≳ 0.4. The diameter of the dust continuum emission is <2 kpc, while the star-formation rate is as high as 1000 M⊙ yr-1. Combined with our stellar mass constraint, this implies an extreme specific star formation rate >80 Gyr-1, especially since there are no clear indications of recent merger activity. Finally, our high signal-to-noise [Cii] measurement revises the observed [Nii]/[Cii] ratio, which suggests a close to solar metallicity, unless the [Cii] flux contains significant contributions from Hii regions. Our observations suggest that ALESS73.1 is a nascent galaxy undergoing its first major burst of star formation, embedded within an unstable but metal-rich gas disk.

Item Type:Article
Keywords:Galaxies: high-redshift, Galaxies: starburst, Galaxies: kinematics and dynamics, Galaxies: ISM.
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Publisher statement:Reproduced with permission from Astronomy & Astrophysics, © ESO 2014.
Date accepted:No date available
Date deposited:24 November 2014
Date of first online publication:May 2014
Date first made open access:No date available

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