A massive and evolved slow-rotating galaxy in the early Universe

TL;DR

This study presents JWST observations of a massive, quiescent galaxy at redshift 3.449, showing it already had slow-rotating, dispersion-dominated kinematics less than 2 billion years after the Big Bang.

Contribution

First direct evidence of a massive, slow-rotating galaxy in the early Universe at z>3, indicating such galaxies formed earlier than previously observed.

Findings

Galaxy exhibits low stellar spin parameter, consistent with dispersion-dominated kinematics.

Features suggest disturbed morphology, implying ongoing or recent formation processes.

Formation of slow rotators occurred within the first 2 billion years of cosmic history.

Abstract

In the contemporary Universe, most galaxies are supported by ordered rotation, yet a significant subset of the most massive and quiescent systems are dominated by random stellar motions and classified as slow rotators. These galaxies are widely thought to arise through processes that remove angular momentum and erase disk-like structures, but when and how this transformation occurs remains uncertain. Slow rotators are expected to be rare at early cosmic times, and observational studies of massive galaxies at high redshift have so far revealed only rapidly rotating systems. Here we report James Webb Space Telescope near-infrared integral field spectroscopy of XMM-VID1-2075, a massive quiescent galaxy at $z=3.449$. The galaxy displays disturbed low-surface-brightness features and a low stellar spin parameter, $\lambda_{R_e} = 0.123^{+0.073}_{-0.023}$, consistent with dispersion-dominated kinematics. These results demonstrate that the formation of slow-rotating massive galaxies was already underway when the Universe was less than 2 Gyr old.