A core in a star-forming disc as evidence of inside-out growth in the early Universe

TL;DR

This paper reports the discovery of a galaxy from the early Universe showing inside-out growth, with a compact core and star-forming disc, providing evidence for early galaxy structural evolution.

Contribution

It presents the first evidence of inside-out galaxy growth during the Epoch of Reionization through detailed morphological analysis.

Findings

Discovery of a galaxy with a compact core and star-forming disc at 700 million years after the Big Bang.

Central stellar density comparable to modern ellipticals despite much lower total mass.

Radial star-formation rate profile rising outward, indicating inside-out growth.

Abstract

The physical processes that establish the morphological evolution and the structural diversity of galaxies are key unknowns in extragalactic astrophysics. Here we report the finding of the morphologically-mature galaxy JADES-GS+53.18343-27.79097, which existed within the first 700 million years of the Universe's history. This star-forming galaxy with a stellar mass of 400 million solar masses consists of three components, a highly-compact core with a half-light radius of less than 100 pc, an actively star-forming disc with a radius of about 400 pc, and a star-forming clump, which all show distinctive star-formation histories. The central stellar mass density of this galaxy is within a factor of two of the most massive present-day ellipticals, while being globally 1000 times less massive. The radial profile of the specific star-formation rate is rising toward the outskirts. This evidence suggests the first detection of inside-out growth of a galaxy as a proto-bulge and a star-forming disc in the Epoch of Reionization.