JWST Finds a Massive Early-Universe Galaxy That Doesn't Spin, the First Slow Rotator Confirmed Less Than 2 Billion Years After the Big Bang

Overview

Astronomers using the James Webb Space Telescope have measured the internal motion of a giant galaxy from the early universe and found that, unlike almost every other young galaxy observed at similar distances, it shows no detectable rotation at all. The galaxy, catalogued as XMM-VID1-2075, appears as it existed when the universe was only 1.8 billion years old, according to UC Davis. The paper describing the result was published on May 4 in Nature Astronomy by a team led by Ben Forrest, a research scientist in the Department of Physics and Astronomy at the University of California, Davis, as reported by Phys.org.

What We Know

XMM-VID1-2075 was originally identified by the MAGAZ3NE survey, which used the W.M. Keck Observatory in Hawai’i to confirm that it is one of the most massive galaxies in the early universe and that it has already stopped forming new stars, according to UC Davis. The galaxy contains several times as many stars as the Milky Way, as reported by ScienceDaily.

The new JWST observations measured the galaxy’s stellar kinematics using the Near-Infrared Spectrograph’s integral field unit, allowing the team to map how stars move within the system, according to Sci.News. Companion imaging with JWST’s Near-Infrared Camera (NIRCam) provided the structural measurements, per Phys.org’s earlier coverage of the preprint.

The galaxy sits at a redshift of about 3.45, has a stellar mass of roughly 330 billion solar masses, and exhibits a stellar velocity dispersion of 379 kilometers per second, according to the technical specifics summarized by Phys.org. Its star-formation rate has dropped below one solar mass per year, confirming the quiescent status earlier inferred from the Keck data, per Phys.org.

What surprised the team was the kinematic signature. “This one in particular did not show any evidence of rotation, which was surprising and very interesting,” Forrest said in the UC Davis announcement. In the local universe, slow rotators of this kind are typically the descendants of giant elliptical galaxies that have weathered a long history of mergers, according to Phys.org. Finding one fully assembled less than 2 billion years after the Big Bang is harder to reconcile with the standard picture in which young massive galaxies retain the angular momentum imparted by the gas that originally collapsed to form them.

The earlier arXiv preprint that laid the groundwork for the Nature Astronomy paper described XMM-VID1-2075 as “the highest redshift slow-rotator so far identified from stellar kinematics,” as reported by Phys.org.

Possible Explanation

Forrest’s team proposes that, rather than the cumulative effect of many smaller mergers that built up slow rotators in the local universe, XMM-VID1-2075 may have been shaped by a single dramatic event. “One possibility is that it is the result not of multiple mergers, but a single collision between two galaxies rotating pretty much in opposite directions,” the UC Davis release notes. The two opposing spins would largely cancel each other, leaving a massive remnant with no net rotation.

Forrest pointed to a specific feature in the JWST imaging as evidence that something disruptive happened. “For this particular galaxy, we see a large excess of light off to the side,” he said in the UC Davis announcement, suggesting debris from an unsettled interaction.

What We Don’t Know

The team’s interpretation rests on a single galaxy. Whether XMM-VID1-2075 is an isolated curiosity or the first of a broader population of early non-rotators will only become clear with similar kinematic measurements of comparable systems, according to Phys.org. Forrest framed the new data as a capability story as much as a result. “James Webb Space Telescope is really pushing the frontier for these kinds of studies,” he said in the UC Davis announcement.

The paper was co-authored with researchers from UC Davis, the Gemini Observatory, York University, Tufts University, the University of Toronto, UC Riverside, UC Irvine, UC Merced, the W.M. Keck Observatory, Ludwig-Maximilians-Universität München, Arizona State University, and the University of Wisconsin-Madison, according to UC Davis. Funding came from NASA, the Space Telescope Science Institute, and the National Science Foundation, per UC Davis.