Galaxies at ‘cosmic noon’: Research gives deep dive into universe’s wild growth spurt

A new University of Kansas survey of distant galaxies using the James Webb Space Telescope reveals never-before-seen star formation and black hole growth at “cosmic noon”—a mysterious epoch 2–3 billion years after the Big Bang, when galaxies like the Milky Way underwent an intense growth spurt.

The results of the MIRI EGS Galaxy and AGN (MEGA) survey appear on the arXiv preprint server and soon will be published by The Astrophysical Journal.

According to KU researchers, galaxies were churning out new stars so intensely during cosmic noon that all galaxies today owe half their stellar mass to stars forged during this epoch. The KU team is seeking public participation in determining the shapes of galaxies and looking for galaxy mergers. Any member of the public can classify galaxies in the Cosmic Collisions Zooniverse project.

“Our goal with this project is to conduct the largest JWST survey in the mid-infrared across multiple bandwidths,” said principal investigator Allison Kirkpatrick, associate professor of physics & astronomy at KU, who led the survey work.

“We are the premier mid-infrared survey to date. The mid-infrared is where dust emits, so we’re looking at dust-obscured galaxies. Dust hides a lot of things, and we want to peer behind the dust. We want to understand how these galaxies are forming stars, how many stars they’re forming and especially how the black holes at their centers are growing.”

Using the JWST’s much-enhanced power in the mid-infrared spectrum, the KU-led team gazed through this cosmic dust to observe galaxies sufficiently far away that arriving light had left their stars during cosmic noon, 10 billion years in the past. They sought to learn more about galaxies with active galactic nuclei (or, supermassive black holes that are rapidly growing in size) in a galaxy-rich deep field near the Ursa Major constellation, considered a “clean window” for extragalactic observation called the “Extended Groth Strip.”

“The Extended Groth Strip is a region of the sky that has now become one of the premier JWST fields,” Kirkpatrick said. “I was on the proposal that received the very first data from the James Webb Space Telescope. This survey is called CEERS—Cosmic Evolution Early Release Science. We got the first images from JWST, and they were of the Extended Groth Strip. Within this region, we’re able to see about 10,000 galaxies—even though the area is only roughly the diameter of the moon.”

Lead author Bren Backhaus, postdoctoral researcher in physics & astronomy at KU, pored through the impressive amount of new JWST data and worked with raw images to produce usable scientific images and information useful to the astronomy community.

“In theory, a galaxy could show up in one image and not another because we’re using different filters,” Backhaus said. “It’s like taking pictures using only red, blue or green light—which eventually create very pretty images. But because the telescope is moving slightly, the images are a little out of frame with each other. The first step is simply receiving the images. The next step involves correcting for known issues with the telescope. For example, there’s a known scratch that appears in every image, and there are dead pixels. The first task is to fix or at least tell the software to ignore those pixels.”

Next, Backhaus aligned the separate images, giving them a reference for how they should overlap. Her final step was to combine the images properly relative to one another.

“I was doing all of that to create our science-ready images,” Backhaus said. “Then, my next goal was to make a catalog—finding a measurable amount of light and recording how much light is coming in through a given filter to support our larger publication. That was my primary work with the data, and I was really excited because I had never worked with photometry data before. It really expanded my skill set, and I got to see beautiful galaxies before anyone else.”

Up to now, the KU-led collaboration has logged 67 hours commanding the JWST. The project recently received approximately 30 more hours of telescope time. Data will be used at KU for research and training for a time before being made available publicly.

“This is the largest amount of JWST data we’ve been able to bring to KU with a principal investigator here, which means KU students have exclusive use of this data for now,” Kirkpatrick said. “It’s not public yet. The way telescope time works is that because so much effort goes into writing a proposal, you’re given a year of exclusive use of the data. Then it gets released into a public database, but only as raw data. Anyone can access it, but they’d have to do their own processing, which has taken months in our case.”

For the time being, only KU physics and astronomy researchers can access “this beautiful dataset,” Kirkpatrick said.

Ongoing research includes finding the galaxies that could be the ancestors of Milky Way-like galaxies today—visible for the first time in the mid-IR thanks to MEGA, measuring how rapidly galaxies form stars and grow their black holes, and looking at how galaxies change their appearance due to mergers over time. All of these projects give researchers an unprecedented look at how galaxies like the Milky Way have “grown up.”

“All my students are working on it,” she said. “It’s a really unique thing for KU right now.”