Letter to the Editor

A nuclear spiral in a dusty star-forming galaxy at z = 2.78

¹ European Southern Observatory, Karl-Schwarzschild Str. 2, D-85748 Garching bei München, Germany
² Max Planck Institute for Astrophysics, Karl-Schwarzschild Str. 1, D-85748 Garching bei München, Germany
³ Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
⁴ South African Radio Astronomy Observatory (SARAO), PO Box 443 Krugersdorp, 1740 South Africa
⁵ Department of Physics, University of Pretoria, Lynnwood Road, Hatfield, Pretoria, 0083 South Africa

^⋆ Corresponding author; hannah.stacey@eso.org

Received: 7 October 2024
Accepted: 4 December 2024

Abstract

The nuclear structure of dusty star-forming galaxies is largely unexplored but harbours critical information about their structural evolution. Here, we present long-baseline Atacama Large (sub-)Millimetre Array (ALMA) continuum observations of a gravitationally lensed dusty star-forming galaxy at z = 2.78. We use a pixellated lens modelling analysis to reconstruct the rest-frame 230 μm dust emission with a mean resolution of ≈55 pc and demonstrate that the inferred source properties are robust to changes in lens modelling methodology. The central 1 kpc is characterised by an exponential profile, a dual spiral arm morphology and an apparent super-Eddington compact central starburst. We find tentative evidence for a nuclear bar in the central 300 pc. These features may indicate that secular dynamical processes play a role in accumulating a high concentration of cold gas that fuels the rapid formation of a compact stellar spheroid and black hole accretion. We propose that the high spatial resolution provided by long-baseline ALMA observations and strong gravitational lensing will give key insights into the formation mechanisms of massive galaxies.