Astronomers have had a unique opportunity to observe a galaxy in the early cosmos that is providing its surrounds with the building blocks required to create later generations of stars and galaxies thanks to a fortunate cosmic alignment.
The far-off galaxy has gas streaming over its edges, as it did only 700 million years after the Big Bang. It is the oldest known commonplace galaxy to exhibit such intricate activity, according to astronomer Hollis Akins, who made the announcement on June 14 at a press conference held in conjunction with the American Astronomical Society convention.
“These results also tell us that this outflow activity seems to be able to shape galaxy evolution, even in this very early part of the universe,” said Akins, a PhD student at the University of Texas in Austin who is about to start. On June 14, he and his colleagues also uploaded their research on arXiv.org.
The galaxy, designated A1689-zD1, is seen in light amplified by Abell 1689, a massive galaxy cluster that has the ability to gravitationally bend and intensify, or lens, light from the oldest galaxies in the cosmos (SN: 2/13/08; SN: 10/6/15). A1689-zD1 produces just approximately 30 suns each year compared to other early universe galaxies found, hence it isn't a particularly brilliant galaxy to our telescopes. However, the intervening cluster increased the brightness of A1689-zD1 by over ten times.
The Atacama Large Millimeter/submillimeter Array, or ALMA, is a large network of radio telescopes in Chile that was used by Akins and colleagues to study the lensed light. A particular oxygen spectral line, a tracer for hot ionized gas, and a carbon spectral line, a tracer for cold neutral gas, were used to map the intensities of the gases. Where the brilliant stars are, hot gas appears, but the team was unprepared for the cold gas to stretch four times as far.
“There has to be some mechanism [to get] carbon out into the circumgalactic medium,” according to Akins.
Only a handful of possibilities might account for that gas leak. Akins speculated that perhaps little galaxies are merging with A1689-zD1 and launching gas farther outside, where it cools. Or perhaps the gas is being forced out by the heat from star formation. The latter would be unexpected given the galaxy's generally slow pace of star production. Other early-universe galaxies contain outflowing gas, but those galaxies are also humming with activity, turning hundreds of solar masses of gas into stars year.
The researchers once more measured the movements of both the cold neutral and hot ionized plasma using the ALMA data. Akins stated at the news conference that the hot gas had a greater overall movement than the cold gas, indicating that it is being pushed from the core of A1689-zD1 to its periphery.
Akins and his coworkers believe that the galaxy's star formation rate is still relatively modest, but the 30-solar-mass stars it produces each year heat the gas sufficiently to drive it away from the galaxy's core. The data point to a more regular bulk flow of gas, which indicates outflows, but the researchers are still delving further into the gas's movement and cannot completely rule out other possibilities.
Akins explained that they believe the colder gas is going beyond the edge of the galaxy because they believe the hot gas expands as it flows out and finally cools. The circumgalactic medium is enriched by this heavy element-rich gas, and following generations of stars will eventually assimilate it (SN: 6/17/15). Cool gas around the galaxy, frequently with less heavy elements, also pulls toward its center due to gravity, allowing A1689-zD1 to continue forming stars.
These A1689-zD1 data demonstrate that this movement of gas occurs in early universe galaxies of all types, not only the superbright, extreme ones. “Knowing how this cycle is working helps us to understand how these galaxies are forming stars, and how they grow,” says Caltech astronomer Andreas Faisst, who was not involved in the study.
A1689-zD1 is still being studied by astronomers. “It’s a great target for follow-up observations,” according to Faisst. With the James Webb Space Telescope, some of Akins' coworkers want to achieve precisely that (SN: 10/6/21).
H. Akins et al. ALMA reveals extended cool gas and hot ionized outflows in a distant star-forming galaxy. American Astronomical Society meeting, Pasadena, Calif., June 14, 2022.
H. Akins et al. ALMA reveals extended cool gas and hot ionized outflows in a typical star-forming galaxy at z=7.13. arXiv: 2206.06939. Submitted June 14, 2022.
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