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
- 14 October 2019
- journal article
- research article
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 490 (4), 4956-4974
- https://doi.org/10.1093/mnras/stz2835
Abstract
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 arcsec (∼1 kpc) 870 $\mu$m 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 arcsec 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 fitted 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 $\mu$m 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 $\eqsim$ resolution to assess either the orientation of any disc on the sky or tits inclination. By stacking our 870 $\mu$m maps we recover faint extended dust continuum emission on ∼4 kpc scales which contributes 13 ± 1 per cent of the total 870 $\mu$m 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 arcsec 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 Gyr ago, represent the formation phase of the earliest galactic-scale components: stellar bulges.
Funding Information
- ERC (321334)
- STFC (ST/P000541/1, ST/P004784/1, ST/P004784/2)
- SONATA BIS (2018/30/E/ST9/00208)
- NSF
This publication has 68 references indexed in Scilit:
- MAGPHYS+photo-z: Constraining the Physical Properties of Galaxies with Unknown RedshiftsThe Astrophysical Journal, 2019
- Resolving the ISM at the Peak of Cosmic Star Formation with ALMA: The Distribution of CO and Dust Continuum in z ∼ 2.5 Submillimeter GalaxiesThe Astrophysical Journal, 2018
- Massive post-starburst galaxies at z > 1 are compact proto-spheroidsMonthly Notices of the Royal Astronomical Society, 2017
- A survey of molecular gas in luminous sub-millimetre galaxiesMonthly Notices of the Royal Astronomical Society, 2013
- UNSTABLE DISKS AT HIGH REDSHIFT: EVIDENCE FOR SMOOTH ACCRETION IN GALAXY FORMATIONThe Astrophysical Journal, 2009
- The Calibration of Mid‐Infrared Star Formation Rate IndicatorsThe Astrophysical Journal, 2007
- A Redshift Survey of the Submillimeter Galaxy PopulationThe Astrophysical Journal, 2005
- A Population of Hot, Dusty Ultraluminous Galaxies atz≈ 2The Astrophysical Journal, 2004
- What determines the strength and the slowdown rate of bars?Monthly Notices of the Royal Astronomical Society, 2003
- Submillimetre-wavelength detection of dusty star-forming galaxies at high redshiftNature, 1998