A massive stellar bulge in a regularly rotating galaxy 1.2 billion years after the Big Bang

TL;DR

This study presents high-resolution observations of a galaxy at redshift 5, revealing a massive, regularly rotating bulge forming rapidly in the early Universe, challenging existing galaxy formation models.

Contribution

It provides evidence that massive bulges and stable rotating disks can form within 1.2 billion years after the Big Bang, faster than current models predict.

Findings

Discovery of a massive, regularly rotating bulge in a z~5 galaxy.

Galaxy's cold gas forms a stable, rotating disk with negligible noncircular motions.

Bulge formation occurs more rapidly than predicted by existing models.

Abstract

Cosmological models predict that galaxies forming in the early Universe experience a chaotic phase of gas accretion and star formation, followed by gas ejection due to feedback processes. Galaxy bulges may assemble later via mergers or internal evolution. Here we present submillimeter observations (with spatial resolution of 700 parsecs) of ALESS 073.1, a starburst galaxy at redshift z~5, when the Universe was 1.2 billion years old. This galaxy's cold gas forms a regularly rotating disk with negligible noncircular motions. The galaxy rotation curve requires the presence of a central bulge in addition to a star-forming disk. We conclude that massive bulges and regularly rotating disks can form more rapidly in the early Universe than predicted by models of galaxy formation.