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

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 $100\ \mathrm{pc}$ , an actively star-forming disc with a radius of about $400\ \mathrm{pc}$ and a star-forming clump, all of which show distinctive star-formation histories. The central stellar mass density of this galaxy is within a factor of $2$ of the most massive present-day ellipticals, while being globally $1,000$ times less massive. The radial profile of the specific star-formation rate is rising towards the outskirts. This evidence suggests a detection of the inside-out growth of a galaxy as a proto-bulge and a star-forming disc in the epoch of reionization.

Nature Astronomy, Advanced Online Publication