Ghostly dusty galaxy reappears in James Webb Space Telescope image

It first appeared as a bright blob from ground-based telescopes, then disappeared completely in images from the Hubble Space Telescope. Today, the ghostly object reappeared as a faint but distinct galaxy in an image from the James Webb Space Telescope (JWST).

Astronomers from the COSMOS-Web collaboration have identified the AzTECC71 object as a dusty star-forming galaxy. Or, in other words, a galaxy that is forming many new stars but is shrouded in a veil of dust that is difficult to see through, dating back almost a billion years after the Big Bang . These galaxies were once thought to be extremely rare in the early universe, but this discovery, along with more than a dozen additional candidates in the first half of the COSMOS-Web data that have not yet been described in the scientific literature , suggest there could be three. 10 times more frequent than expected.

“This thing is a real monster,” said Jed McKinney, a postdoctoral researcher at the University of Texas at Austin. “Even though it looks like a small blob, it’s actually forming hundreds of new stars every year. And the fact that even something this extreme is barely visible in the most sensitive imaging from our new telescope is very exciting to me. This potentially tells us there is a whole population of galaxies hiding from us.”

If this conclusion is confirmed, it suggests that the early universe was much dustier than previously thought.

The team published its findings in The Astrophysics Journal.

The COSMOS-Web project, JWST’s largest initial research initiative, co-led by UT Austin associate professor Caitlin Casey, aims to map up to 1 million galaxies from a portion of the sky the size of three full moons. The goal is in part to study the earliest structures of the universe. The team of more than 50 researchers benefited from 250 hours of observation during the first year of JWST and received a first batch of data in December 2022, with more arriving through January 2024.

A dusty star-forming galaxy is difficult to see in optical light because much of its starlight is absorbed by a veil of dust and then re-emitted at redder (or longer) wavelengths. Before JWST, astronomers sometimes called them “hubble dark galaxies”, referring to the previously most sensitive space telescope.

“Until now, the only way we were able to see the galaxies of the early universe was from an optical perspective with Hubble,” McKinney said. “This means that our understanding of the evolutionary history of galaxies is biased because we only see the unobscured and less dusty galaxies.”

This galaxy, AzTECC71, was first detected as an indistinct blob of dust emission by a camera on the James Clerk Maxwell Telescope in Hawaii that sees in wavelengths between far infrared and microwaves . The COSMOS-Web team then spotted the object in data collected by another team using the ALMA telescope in Chile, which has higher spatial resolution and can see in infrared. This allowed them to pinpoint the location of the source. When they looked at the JWST data in infrared at a wavelength of 4.44 microns, they found a faint galaxy in exactly the same location. In shorter wavelengths of light, less than 2.7 microns, it was invisible.

The team is now working to discover more of these faint JWST galaxies.

“With JWST, we can study for the first time the optical and infrared properties of this hidden, heavily dust-obscured population of galaxies,” McKinney said, “because it is so sensitive that it can not only look into the farthest reaches of the planet.” the universe, but it can also pierce the thickest dusty veils. »

The team estimates that the galaxy is observed at a redshift of around 6, which corresponds to around 900 million years after the Big Bang.

The authors of the UT Austin study are McKinney, Casey, Olivia Cooper (National Science Foundation graduate researcher), Arianna Long (NASA Hubble Fellow), Hollis Akins and Maximilien Franco.