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Testing star formation laws in a starburst galaxy at redshift 3 resolved with ALMA.

Sharda, P. and Federrath, C. and da Cunha, E. and Swinbank, A. M. and Dye, S. (2018) 'Testing star formation laws in a starburst galaxy at redshift 3 resolved with ALMA.', Monthly notices of the Royal Astronomical Society., 477 (4). pp. 4380-4390.


Using high-resolution (sub-kiloparsec scale) data obtained by ALMA, we analyse the star formation rate (SFR), gas content, and kinematics in SDP 81, a gravitationally lensed starburst galaxy at redshift 3. We estimate the SFR surface density (SFR) in the brightest clump of this galaxy to be 357+135 −85 M yr−1 kpc−2 , over an area of 0.07 ± 0.02 kpc2. Using the intensity-weighted velocity of CO (5–4), we measure the turbulent velocity dispersion in the plane of the sky and find σv, turb = 37 ± 5 km s−1 for the clump, in good agreement with previous estimates along the line of sight. Our measurements of the gas surface density, freefall time, and turbulent Mach number allow us to compare the theoretical SFR from various star formation models with that observed, revealing that the role of turbulence is crucial to explaining the observed SFR in this clump. While the Kennicutt–Schmidt (KS) relation predicts an SFR surface density of SFR, KS = 52 ± 17 M yr−1 kpc−2, the single-freefall model by Krumholz, Dekel, and McKee (KDM) predicts SFR, KDM = 106 ± 37 M yr−1 kpc−2. In contrast, the multifreefall (turbulence) model by Salim, Federrath, and Kewley (SFK) gives SFR,SFK = 491+139 −194 M yr−1 kpc−2 . Although the SFK relation overestimates the SFR in this clump (possibly due to the negligence of magnetic fields), it provides the best prediction among the available models. Finally, we compare the star formation and gas properties of this galaxy to local star-forming regions and find that the SFK relation provides the best estimates of SFR in both local and high-redshift galaxies.

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:05 April 2018
Date deposited:08 June 2018
Date of first online publication:07 April 2018
Date first made open access:08 June 2018

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