A University of Kansas survey of a swath of the universe using the James Webb Space Telescope has revealed that active galactic nuclei (AGNs) — rapidly increasing supermassive black holes — are much rarer than many astronomers previously assumed.
The findings, made with JWST’s Medium Infrared Instrument (MIRI), suggest that our universe may be a little more stable than assumed. The work also provides insight into observations of faint galaxies, their properties, and the challenges of AGN identification.
A new paper detailing the JWST research, which was conducted under the auspices of the Cosmic Evolutionary Launch Science (CEERS) Program, has been made available at the following website: arXiv Prior to the publication of the official peer review in Astrophysical Journal.
The work, which was headed by Alison Kirkpatrick, assistant professor of physics and astronomy at Kuwait University, focused on a long-studied region of the universe dubbed the Groth Bar, which lies between the constellations Ursa Major and Boötes. But previous examinations of the region relied on a less powerful generation of space telescopes.
“Our observations were taken last June and December, and we aimed to describe what galaxies looked like during the peak of star formation in the universe,” Kirkpatrick said. “This is a look back in time from 7 to 10 billion years in the past. We used the mid-infrared instrument on the James Webb Space Telescope to look at dust in galaxies that existed 10 billion years in the past, and this dust” can mask formation. of stars, and it can hide growing supermassive black holes. So I did the first survey to look for these supermassive black holes lurking at the centers of these galaxies.”
While every galaxy contains a supermassive black hole at the center, active galactic galaxies are more spectacular turbulences that pull in gas and exhibit a luminosity absent from typical black holes.
Kirkpatrick and several fellow astrophysicists predicted that the higher-resolution survey by the James Webb Space Telescope would locate many more active active galaxies than the previous survey with the Spitzer Space Telescope. However, even with MIRI’s boost in power and sensitivity, a few additional AGNs were found in the new survey.
“The results looked completely different from what I expected, which led to my first big surprise,” Kirkpatrick said. “One of the important discoveries was the rarity of rapidly growing supermassive black holes. This discovery raised questions about where these objects might be located. As it turns out, these black holes are likely to grow at a slower pace than previously thought, which is interesting, given the “ The galaxies I examined are similar to our own Milky Way from the past. Previous observations with Spitzer have only allowed us to study the brightest, most massive galaxies that contain rapidly growing supermassive black holes, making them easier to spot.”
An important puzzle in astronomy, Kirkpatrick said, is understanding how typical supermassive black holes, such as those found in galaxies like the Milky Way, grow and affect their host galaxy.
“The results of the study indicate that these black holes do not grow rapidly, absorb limited material, and may not significantly affect their host galaxies,” she said. “This discovery opens up a whole new perspective on the growth of black holes since our current understanding is largely based on the more massive black holes in the largest galaxies having large effects on their hosts, but it is likely that smaller black holes in these galaxies have a significant impact.” no.”
Another surprising finding, said the Kuwait University astronomer, is the absence of dust in these galaxies.
“With the James Webb Space Telescope, we can identify much smaller galaxies than ever before, including those as big as the Milky Way or even smaller, which was previously impossible at these redshifts (cosmic distances),” Kirkpatrick said. “Typically, more massive galaxies contain abundant dust due to rapid star formation rates. I had assumed that lower-mass galaxies would also contain large amounts of dust, but they did not, which defies my expectations and makes another interesting discovery.”
According to Kirkpatrick, this work changes the understanding of how galaxies grow, especially in relation to the Milky Way.
“Our black hole appears to be completely calm, not showing much activity,” she said. “One of the big questions about the Milky Way is whether it was active at all or went through an AGN phase. If most galaxies, like our own, lack a detectable AGN, that could mean that our black hole wasn’t more active in the past. Ultimately, this is The knowledge will help constrain and measure black hole masses, and shed light on the origins of black hole growth, which remain an unanswered question.
Kirkpatrick was recently awarded a new senior time at JWST to conduct a larger field survey of the Extended Groth Strip using MIRI. Her current paper included about 400 galaxies. Its upcoming survey (MEGA: MIRI EGS Galaxy and AGN Survey) will include about 5,000 galaxies. The work is scheduled to take place in January 2024.
Allison Kirkpatrick et al., CEERS Principal Paper VII: JWST/MIRI Reveals Faint Number of Galaxies in Cosmic Noon Unseen by Spitzer, arXiv (2023). DOI: 10.48550/arxiv.2308.09750
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