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An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field : high-resolution dust continuum morphologies and the link between sub-millimetre galaxies and spheroid formation.

Gullberg, B. and Smail, I. and Swinbank, A. M. and Dudzevičiūtė, U. and Stach, S. M. and Thomson, A. P. and Almaini, O. and Chen, C. C. and Conselice, C. and Cooke, E. A. and Farrah, D. and Ivison, R. J. and Maltby, D. and Michałowski, M. J. and Simpson, J. M. and Scott, D. and Wardlow, J. L. and Weiss, A. (2019) 'An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field : high-resolution dust continuum morphologies and the link between sub-millimetre galaxies and spheroid formation.', Monthly notices of the Royal Astronomical Society., 490 (4). pp. 4956-4974.


We present an analysis of the morphology and profiles of the dust continuum emission in 153 bright sub-millimetre galaxies (SMGs) detected with ALMA at signal to noise ratios of >8 in high-resolution 0′′.18 (∼1 kpc) 870 μm maps. We measure sizes, shapes and light profiles for the rest-frame far-infrared emission from these luminous star-forming systems and derive a median effective radius (Re) of 0′′.10 ± 0′′.04 for our sample with a median flux of S870=5.6 ± 0.2 mJy. We find that the apparent axial ratio (b/a) distribution of the SMGs peaks at b/a ∼ 0.63 ± 0.02 and is best described by triaxial morphologies, while their emission profiles are best fit by a Sérsic model with n ≃ 1.0 ± 0.1, similar to exponential discs. This combination of triaxiality and n ∼ 1 Sérsic index are characteristic of bars and we suggest that the bulk of the 870 μm dust continuum emission in the central ∼2 kpc of these galaxies arises from bar-like structures. As such we caution against using the orientation of shape of the bright dust continuum emission at ≂ resolution to assess either the orientation of any disc on the sky or tits inclination. By stacking our 870 μm maps we recover faint extended dust continuum emission on ∼4 kpc scales which contributes 13 ± 1% of the total 870 μm emission. The scale of this extended emission is similar to that seen for the molecular gas and rest-frame optical light in these systems, suggesting that it represents an extended dust and gas disc at radii larger than the more active bar component. Including this component in our estimated size of the sources we derive a typical effective radius of ≃ 0′′.15 ± 0′′.05 or 1.2 ± 0.4 kpc. Our results suggest that kpc-scale bars are ubiquitous features of high star-formation rate systems at z ≫ 1, while these systems also contain fainter and more extended gas and stellar envelopes. We suggest that these features, seen some 10–12 Gyrs ago, represent the formation phase of the earliest galactic-scale components: stellar bulges.

Item Type:Article
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Publisher statement:This article has been accepted for publication in the Monthly notices of the Royal Astronomical Society ©: 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:30 September 2019
Date deposited:17 October 2019
Date of first online publication:14 October 2019
Date first made open access:17 October 2019

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