Astronomers using the James Webb Space Telescope have made a surprising discovery about a galaxy long, long ago and far, far away: It isn’t rotating.
That’s something only seen in the most massive, mature galaxies that are closer to us in space and time, said Ben Forrest, a research scientist in the Department of Physics and Astronomy at the University of California, Davis, and first author on the paper published May 4 in Nature Astronomy.
“This one in particular did not show any evidence of rotation, which was surprising and very interesting,” Forrest said.
According to current theories, as the first galaxies formed, angular momentum from inflowing gas and the influence of gravity set them spinning.
Over many billions of years, some galaxies, especially those within galaxy clusters, merged with each other multiple times and their combined rotations added to or partly canceled each other. That’s why some galaxies that are closest to Earth (and therefore also relatively recent) can show little overall rotation but a lot of random movement of stars within them.
This process should take an enormously long time, so it’s surprising that galaxy XMM-VID1-2075 had achieved this state when the universe was less than 2 billion years old.
Forrest and colleagues in the MAGAZ3NE (Massive Ancient Galaxies at z>3 NEar-Infrared) survey had previously observed this galaxy with the W.M. Keck observatory in Hawaiʻi.
“Previous MAGAZ3NE observations had confirmed this was one of the most massive galaxies in the early universe, with already several times as many stars as our Milky Way, and also confirmed that it was no longer forming new stars, making it a compelling target for follow-up observations,” Forrest said.
Pushing the frontiers
The team used the James Webb Space Telescope to take a closer look at XMM-VID1-2075 and two other galaxies of similar age. They were able to measure the relative movement of material inside them.
“This type of work has been done a lot with nearby galaxies because they’re closer and larger and so you can do these kinds of studies from the ground, but it’s very difficult to do with high redshift galaxies because they appear a lot smaller in the sky,” Forrest said. “(James Webb Space Telescope) is really pushing the frontier for these kinds of studies.”
Of the three galaxies they sampled, one is clearly rotating, one is “kind of messy,” and one has no rotation but a lot of random motion, Forrest said. “That’s consistent with some of the most massive galaxies in the local universe, but it was a bit surprising to find it so early on.”
The lack of color contrast in the image of XMM-VID1-2075 (left panel) shows a lack of rotational movement compared to the other two galaxies (center and right).
How did this galaxy become a “slow rotator” in less than 2 billion years? 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. That idea is supported by the team’s observations.
“For this particular galaxy, we see a large excess of light off to the side. And so that’s suggestive of some other object which has come in and is interacting with the system and potentially changing its dynamics,” Forrest said.
The astronomers are continuing to look for other, similar objects in the early universe. By comparing their observations with simulations, they can test theories about galaxy formation.
“There are some simulations that predict that there will be a very small number of these non-rotating galaxies very early in the universe, but they expect them to be quite rare. And so this is one way in which we can test these simulations and really figure out how common they are, and that can then give us information about whether our theories of this evolution are correct,” Forrest said.
Additional co-authors on the paper are: Brian C. Lemaux, UC Davis and Gemini Observatory, Hawaiʻi; Adam Muzzin and Adit H. Edward, York University, Toronto; Danilo Marchesini, Richard Pan and Nehir Ozden, Tufts University; Jacqueline Antwi-Danso, University of Toronto; Wenjun Chang, UC Riverside; M. C. Cooper and Stephanie M. Urbano Stawinski, UC Irvine; Percy Gomez, W. M. Keck Observatory, Kamuela, Hawaiʻi; Lucas Kimmig and Rhea-Silvia Remus, Ludwig-Maximilians-Universität München, Germany; Ian McConachie, University of Wisconsin-Madison; Allison Noble, Arizona State University; and Gillian Wilson and M. E. Wisz, UC Merced.
The work was supported by grants from NASA, the Space Telescope Science Institute and National Science Foundation.