Astronomers discover a swarm of galaxies orbiting a very bright galaxy

The massive, extremely bright galaxy W0410-0913 and its surroundings, were seen 12 billion years ago. Zooming in on W0410-0913 shows a map of the velocity of gas in the galaxy, more specifically carbon monoxide: blue means the gas is coming towards us, while red means it is receding from us. In other words, the galaxy is rotating. Credit: M. Ginolfi & G. Jones/VLT/ESO

Using the Very Large Telescope and the ALMA Radio Telescope in Chile, a team of astronomers, including researchers from the Niels Bohr Institute, has discovered a swarm of galaxies orbiting around the periphery of a highly luminous galaxy and strongly forming stars in the early universe. The observation provides important clues to how exceptionally bright galaxies grow, and how they evolve into active quasars, radiating light through most of the visible universe.

A fundamental issue in astronomy is the question of how galaxies Form, grow and develop.

As part of their evolution, most galaxies seem to build a supermassive black hole at their center. These gravity monsters sometimes swallow nearby gases and stars, emitting them excess energy As powerful planes, a phenomenon known as quasars.

From galaxy to quasar

Many details about the transition from “ordinary” galaxies to quasars are still unknown. But in a new study published in Nature Communicationsa team of astronomers led by Michel Ginolfi at ESO, Garching, may have come a step closer to understanding this evolution.

“Before they evolve into a full-fledged quasar, some galaxies are thought to go through a very dusty and ‘active’ phase in terms of star formation and gas accretion at their centre, supermassive black holesGinolfi explains. We set out to design an experiment to learn more about this transition. “

Ginolfi and his collaborators focused on an already known galaxy, W0410-0913, one of the brightest, most massive and gas-rich in the distant universe, seen 12 billion years in time.

The dust is heated by energy from starlight and the central black hole, causing it to glow and firing the galaxy through infrared light. This has led to this type of galaxy being called hot dust-shielded galaxies (also known colloquially as “hot DOGs”).

Astronomers discover a swarm of galaxies orbiting a very bright galaxy

Muse tool. Credit: ESO / Eric Le Roux

3D Galaxies

Because the evolution of galaxies is inextricably linked to their surroundings, Ginolfi and his team—whose core is somewhat unusually made up of early-career researchers—decided to observe W0410-0913 using the “MUSE” instrument at the Very Large Telescope (VLT) in Chile. This advanced instrument allowed them to study an area 40 times larger than the galaxy itself.

Study co-author Peter Laursen of the Cosmic Dawn Center in Copenhagen. He explains: “Observations have revealed that W0410-0913 is surrounded by a swarm of at least 24 smaller galaxies. The great thing about the MUSE instrument is that we can measure not only its position in the sky, but also its distance along our galaxy. Line of sight. In other words, we can measure Their positions are three-dimensional.”

Although this indicates that W0410-0913 exists in a region at least ten times denser than the ordinary universe, this is not entirely unexpected, as hot dog DOGs are believed to actually live in dense environments.

Galaxy car accident

Moreover, while W0410-0913 is seen at a time when the universe was 1/8 its current age, it is already ten times larger than our Milky Way. Growing such a large galaxy in such a short time, feeding a supermassive black hole would require a huge supply of new material. All this fits perfectly with the traditional picture that huge galaxies grow by accretion of gases and satellite galaxies, which are attracted from intergalactic space by their immense gravity.

Indeed, in such a dense environment, the rate of interactions and mergers of galaxies would be expected to be very high. After being hit by such bombardment, astronomers speculated that W0410-0913 would be a car wreck of chaotically swirling clumps of gas and stars.

However, when looking at older observations obtained with the ALMA radio antenna located just 300 kilometers northeast of the VLT, Ginolfi and colleagues were able to measure the internal motion of the gas inside W0410-0913.

And here a completely different picture appeared.

Astronomers discover a swarm of galaxies orbiting a very bright galaxy

3D Galaxies: Stereoscopic view of the image shown at the beginning of this article: If you cross your eyes and focus on the blue ball showing the galaxy W0410-0913, you should be able to get an idea of ​​the 3D mode of all the other galaxies (it may take some time to adjust) . The squares in the back plane are 200,000 light-years on each side. The distance along the line-of-sight was estimated using Lyman’s hydrogen-alpha spectral line, but is uncertain due to the non-specific effect on the motion of satellite galaxies by W0410-0913. Credit: Peter Laursen

Throwing pebbles on a glass plate

Surprisingly, ALMA observations revealed that W0410-0913 appears not to have been affected by interactions with companion galaxies at all. According to the observations, the gas is well circulated and organized around the central black hole. Regulated, but surprisingly fast, with speeds of up to 500 km / s.

“When we pair the results from the two very different telescopes, we see a picture of how the most massive and dusty galaxies evolve. This type of galaxy, a vital stage in the transition from a dusty galaxy and star-forming to a quasar, tends to grow in extremely dense environments,” Ginolfi says. “However, despite the expected frequent mergers with other galaxies, these gravitational interactions are not necessarily destructive—they feed the central galaxy and spin the gas a bit, but leave it practically intact. A bit like throwing pebbles on a sheet of steel glass: you might scratch it , but you won’t break it…”

Michel Genolfi’s observations provide the first clues to the multiscale process driving the evolution of rare and extreme groups of hot, dust-obscured galaxies. It grows in special dense habitats, but the interaction with its companions can be pleasant.

As an example of this galactic car accident, the study came close to not being done at all, when Michele Ginolfi got stuck in a traffic jam in Rome and had to make the suggestion to use his phone from his car, minutes before the deadline.

Supermassive black holes discovered inside dying galaxies in the early universe

more information:
M. Ginolfi et al, Discovery of companion galaxies around the hot, highly luminous, dust-obscured galaxy W0410-0913, Nature Communications (2022). DOI: 10.1038 / s41467-022-32297-x

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