New research shows that during the early universe cosmic filaments ferried cold gas and embryonic, node-shaped galaxies to a dark matter halo, where it all clumped together to form massive galaxies. The larger the galaxy, the more cold gas it needs to coalesce and to grow from a source of cold molecular gases totaling as much as 100 billion times the mass of our sun.
“Where,” asked University of Iowa astronomers in a new study, “did these early, super-sized galaxies get that much cold gas when they were hemmed in by hotter surroundings?”
Dark-Matter Halo Reservoir
New observational evidence revealed that cold gas pipelines that knifed through the hot atmosphere in the dark matter halo of an early massive galaxy, supplying the materials for the galaxy to form stars. The scientists studied a gaseous region surrounding a previously unstudied, massive galaxy formed when the universe was about 2.5 billion years old, or just 20% of its present age. It took the team five years to pinpoint through its redshift its exact location and distance using the Atacama Large Millimeter/Submillimeter Array, to peer through because of the target galaxy’s opaque, dusty environment.
“It is the prototype, the first case where we detected a halo-scale stream that is feeding a very massive galaxy,” says Hai Fu, associate professor in Iowa’s Department of Physics and Astronomy and the study’s lead and corresponding author. “Based on our observations, such streams can fill up the reservoir in about a billion years, which is far shorter than the amount of time that was available to the galaxy at the epoch that we were observing.”
Chemical Fingerprints Confirm
Crucially, the researchers located two background quasars that are projected at close angular distances to the target galaxy, much like how Jupiter and Saturn’s motion drew them closer to each other when viewed from Earth during the Great Conjunction last December. Due to this unique configuration, the quasars’ light penetrating the halo gas of the foreground galaxy left chemical “fingerprints” that confirmed the existence of a narrow stream of cold gas.
Those chemical fingerprints showed the gas in the streams had a low concentration of heavy elements such as aluminum, carbon, iron, and magnesium. Since these elements are formed when the star is still shining and are released into the surrounding medium when the star dies, the researchers determined the cold gas streams must be streaming in from outside, rather than being expelled from the star-making galaxy itself.
Quasars Unveil the Stream
“Among the 70,000 starburst galaxies in our survey, this is the only one associated with two quasars that are both nearby enough to probe the halo gas. Even more, both quasars are projected on the same side of the galaxy so that their light can be blocked by the same stream at two different angular distances.” Fu says. “So, I feel extremely fortunate that nature provided us this opportunity to detect this major artery leading to the heart of a phenomenal galaxy during its adolescence.”
Source: “A long stream of metal-poor cool gas around a massive starburst galaxy at Z=2.67,” was published in the Astrophysical Journal Feb. 24.
Image credit top of page: shows filaments in massive galaxy cluster using the C-EAGLE simulation.