A team of international astronomers has discovered a swarm of galaxies orbiting a hyperluminous and strongly star-forming galaxy in the early Universe.
Using the European Southern Observatory’s Very Large Telescope (VLT) and the ALMA radio telescope in Chile, the team led by Michele Ginolfi of ESO in Garching focused on an already known galaxy, W0410-0913, one of the brightest, most massive and most gaseous -rich galaxies in the distant universe seen 12 billion years ago in time.
Galaxies like W0410-0913 are known as hot dusty galaxies (colloquially known as “hot DOGs”). These galaxies harbor active supermassive black holes at their cores and emit enormous amounts of infrared light while their visible light is blocked by dust.
Ginolfi and his team decided to observe W0410-0913 with the “MUSE” instrument on the Very Large Telescope (VLT) in Chile. The Multi-Unit Spectroscopic Explorer, or MUSE, is an integral field spectrograph that enabled the team to study a region 40 times larger than the galaxy itself. The advanced tool is capable of covering as many as 90,000 spectra simultaneously get a wide field of view.
“The observations showed that W0410-0913 is surrounded by a swarm of as many as 24 smaller galaxies. The cool thing about the MUSE instrument is that not only can we measure their position in the sky, but also their distance along our line of sight. In other words, we can measure their 3D positions,” Peter Laursen of the Cosmic Dawn Center in Copenhagen, who also contributed to the study.
According to the researchers, while W0410-0913 was visible when the Universe was 1/8th its present age, it is already 10 times more massive than our Milky Way. Growing such a huge galaxy in such a short time and feeding a huge black hole requires a substantial supply of fresh material.
“Indeed, in such a dense environment, the rate of galaxy interactions and mergers is expected to be very high,” the researchers said. They expected W0410-0913 to be a wrecked car made of chaotically swirling blobs of gas and stars
Ginolfi and his team dug up old observations from the ALMA radio antennas, located just 300 km northeast of the VLT, and found that W0410-0913 appeared unperturbed by interactions with companion galaxies at all. According to the observations, its gas rotates nicely and orderly around the central black hole, at speeds of up to 500 km/s.
“When we couple the results from the two very different telescopes, we see a picture of how the most massive and dustiest galaxies can evolve to grow in very dense environments,” says Ginolfi.
The study was published in the journal Nature Communications.