Go back in time to look at the shape of ancient galaxies

The deeper you look into the Universe, the farther in time you return. Sometimes you can even dig too deep and see “young” galaxies resembling the Milky Way, located 12 billion years from us.

Go back in time to look at the shape of ancient galaxies

An artistic interpretation of the Milky Way's predecessor in the early Universe. Placed against the backdrop of a quasar glistening through the “super-halo” of gaseous hydrogen surrounding the galaxy.

Scanning old objects of the Universe, astronomers manage to understand how our galaxy looked in its youth.

With the help of the Atakam large millimeter-range lattice (ALMA), researchers were able to find "casts" of galaxies like ours, when their star formation only gained speed. Then the universe grew to 2 billion years. Since light has speed, looking deep into space means that you literally look into the past, admiring galaxies 12 billion years away from Earth. The modern cosmos is 13.8 billion years old.

Considering two ancient galaxies in infrared wavelengths, scientists noticed that in early development they had elongated hydrogen gas discs that were significantly superior to smaller areas of star formations inside. They also saw rotating gas and dust disks and rapidly forming stars (up to 100 solar masses per year). To see the galaxies ALMA J081740.86 + 135138.2 and ALMA J120110.26 + 211756.2, it was necessary to use the light of two quasars in the background. These are supermassive black holes surrounded by bright accretion disks. They are considered centers of active galaxies.

Go back in time to look at the shape of ancient galaxies

Compositional image of a young galaxy, similar to the Milky Way, separated by 12 billion light years, as well as a background quasar, located 12.5 billion light years.

Usually it’s hard to look at galaxies before a quasar, because the quasars are very bright, and the young galaxy is weak. But ALMA was able to track the infrared light from the ionized carbon of galaxies, shining by itself, as well as the silhouette of hydrogen in the glow of quasars. Carbon, emitting light at a wavelength of 158 micrometers (far infrared region), characterizes the structure of each galaxy, and emissions of infrared light from dust show areas of stellar birth.

Luminous carbon also gave clues to the structure of galaxies. It turned out that he shifted from hydrogen gas, which was originally seen by astronomers. This means that galactic gases extend far from a dense region of carbon, indicating that each galaxy is endowed with a large hydrogen halo.

Considering the foreground objects, “we expected to see a weak burst directly above the quasar, and instead noticed bright galaxies at a great distance from the quasar,” said astrophysicist J. Xavier Prohaska of the University of California (Santa Cruz). The data also showed that young galaxies have already begun to rotate, and this is a sign of spiral galaxies, like the Milky Way.

The search for such early galaxies began in 2003, when Prohaska was working on the idea of ​​using the spectra of quasars and the wavelengths of light they emit to find in the foreground of the galaxy. This method is called Lyman-alpha damped systems, because hydrogen gas blocks certain wavelengths of light from the quasar, revealing the presence and extent of gas.

“ALMA helped resolve a multi-year debate about galaxy formation,” says Chris Carilli, an astronomer at the National Radio Astronomy Observatory in Socorro, New Mexico. “It turned out that some very early galaxies have halos that are expanded much more than previously thought,” he said, adding that these halos “may represent future material for the growth of the galaxy.”

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