New images challenge theories of galaxy evolution
Astrophysicists from the University of Texas at Austin have identified a number of images of barred galaxies which challenge accepted theories of how galaxies evolve
New images from NASA’s James Webb Space Telescope (JWST) reveal for the first time galaxies with stellar bars – elongated features of stars stretching from the centres of galaxies into their outer disks – at a time when the universe was a mere 25% of its present age.
The finding of so-called barred galaxies, similar to our Milky Way, this early in the universe will require astrophysicists to refine their theories of galaxy evolution.
Prior to JWST, images from the Hubble Space Telescope had never detected bars at such young epochs. In a Hubble image, one galaxy, EGS-23205, is little more than a disk-shaped smudge, but in the corresponding JWST image taken this past summer, it’s a beautiful spiral galaxy with a clear stellar bar.
Shardha Jogee, professor of astronomy at The University of Texas at Austin, said: “I took one look at these data, and I said, ‘We are dropping everything else!’
“The bars hardly visible in Hubble data just popped out in the JWST image, showing the tremendous power of JWST to see the underlying structure in galaxies.”
The data came from the Cosmic Evolution Early Release Science Survey (CEERS), led by UT Austin professor, Steven Finkelstein.
The team identified another barred galaxy, EGS-24268, also from about 11 billion years ago, which makes two barred galaxies existing farther back in time than any previously discovered. They have also highlighted four other barred galaxies from more than 8 billion years ago.
Yuchen ‘Kay’ Guo, a graduate student who led the analysis, said: “For this study, we are looking at a new regime where no one had used this kind of data or done this kind of quantitative analysis before, so everything is new. It’s like going into a forest that nobody has ever gone into.”
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Bars play an important role in galaxy evolution by funnelling gas into the central regions, boosting star formation.
Jogee said: “Bars solve the supply chain problem in galaxies. Just like we need to bring raw material from the harbour to inland factories that make new products, a bar powerfully transports gas into the central region where the gas is rapidly converted into new stars at a rate typically 10 to 100 times faster than in the rest of the galaxy.”
Bars also help to grow supermassive black holes in the centres of galaxies by channelling the gas part of the way. The discovery of bars during such early epochs shakes up galaxy evolution scenarios in several ways.
Jogee said: “This discovery of early bars means galaxy evolution models now have a new pathway via bars to accelerate the production of new stars at early epochs.”
And the very existence of these early bars challenges theoretical models as they need to get the galaxy physics right in order to predict the correct abundance of bars. The team will be testing different models in their next papers.
JWST can unveil structures in distant galaxies better than Hubble for two reasons: firstly, its larger mirror gives it more light-gathering ability, allowing it to see farther and with higher resolution; and secondly, it can see through dust better as it observes at longer infrared wavelengths than Hubble.
Undergraduate students Eden Wise and Zilei Chen played a key role in the research by visually reviewing hundreds of galaxies, searching for those that appeared to have bars, which helped narrow the list to a few dozen for the other researchers to analyse with a more intensive mathematical approach.
The research is the Astrophysical Journal Letters.
Image 1: The power of JWST to map galaxies at high resolution and at longer infrared wavelengths than Hubble allows it to look through dust and unveil the underlying structure and mass of distant galaxies. This can be seen in these two images of the galaxy EGS23205, seen as it was about 11 billion years ago. In the HST image (left, taken in the near-infrared filter), the galaxy is little more than a disk-shaped smudge obscured by dust and impacted by the glare of young stars, but in the corresponding JWST mid-infrared image (taken this past summer), it’s a beautiful spiral galaxy with a clear stellar bar.
Image 2: Montage of JWST images showing six example barred galaxies, two of which represent the highest lookback times quantitatively identified and characterized to date. The labels in the top left of each figure show the lookback time of each galaxy, ranging from 8.4 to 11 billion years ago (Gyr), when the universe was a mere 40% to 20% of its present age.
© NASA/ CEERS/ University of Texas at Austin.