Astronomers discover a swarm of galaxies orbiting a hyper-luminous galaxy
A fundamental issue in astronomy is the question of how galaxies form, grow, and evolve.
Using the Very Large Telescope and the radio telescope ALMA in Chile, a team of astronomers including researchers from the Niels Bohr Institute has discovered a swarm of galaxies orbiting the surroundings of a hyper-luminous and vigorously star-forming galaxy in the early universe. The observation provides important clues to how exceptionally bright galaxies grow, and to how they evolve into energetic quasars, beaming light across most of the observable universe.
A fundamental issue in astronomy is the question of how galaxies form, grow, and evolve.
As a part of their evolution, most galaxies seem to foster a supermassive black hole in their center. These gravitational monsters occasionally swallow nearby gas and stars, spewing out excess energy as powerful jets, a phenomenon known as a quasar.
From galaxy to quasar
Many details about the transition from “normal” galaxies to quasars are still unknown. But in a new study published in Nature Communications, a team of astronomers led by Michele Ginolfi at ESO, Garching, may have come a step closer to understanding this evolution.
“Before evolving into a full-blown quasar, some galaxies are thought to go through a phase of being very dusty, and very ‘active’ in terms of star formation and accretion of gas onto their central, supermassive black holes,” Ginolfi explains. “We set out to design an experiment to learn more about this transition phase.”
Ginolfi and his collaborators focused on an already known galaxy, W0410-0913, one of the brightest, most massive and gas-rich galaxies in the distant universe, seen 12 billion years back in time.
The dust is heated by the energy from starlight and the central black hole, making it glow and divulging the galaxy through its infrared light. This has led to this type of galaxies being called hot dust-obscured galaxies (also known colloquially as “hot DOGs”).
Galaxies in 3D
Because the evolution of galaxies is inherently connected with their surroundings, Ginolfi and his team—whose core somewhat atypically consisted mostly of early career researchers—decided to observe W0410-0913 with the “MUSE” instrument at the Very Large Telescope (VLT) in Chile. This advanced tool allowed them to study a region 40 times wider than the galaxy itself.
Peter Laursen from the Cosmic Dawn Center in Copenhagen participated in the study. He explains: “The observations revealed that W0410-0913 is surrounded by a swarm of no fewer than 24 smaller galaxies. The cool thing about the MUSE instrument is that we can measure not only their position on the sky, but also their distance along our line of sight. In other words, we can measure their 3D positions.”
Although this implies that W0410-0913 resides in a region at least ten times more dense than the average universe, this is not entirely unexpected, since hot DOGs are indeed thought to live in dense environments.
