Early galaxies found hiding in “super halos” of hydrogen

Early galaxies found hiding in “super halos” of hydrogen

PanARMENIAN.Net - Astronomers have observed a pair of Milky Way-like galaxies so distant they can be seen when the Universe was only eight percent of its current age.

The discovery, which will teach us about the early history of our galaxy, comes thanks to a breakthrough in galaxy detection methods, Wired reports.

For decades, astronomers have found distant galaxies by detecting the way their gas absorbs light from a bright quasar in the background. But actually finding the light emitted by these same galaxies has been difficult, because of the bright background.

"Imagine a tiny firefly next to a high-power search light," said Marcel Neeleman from the University of California, Santa Cruz, author of the new paper, published in Science. "That's what astronomers are up against when it comes to observing these youthful versions of our home galaxy."

"We can now see the galaxies themselves, which gives us an amazing opportunity to learn about the earliest history of our own galaxy and others like it."

Neelman and his colleagues used the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile to look at two distant galaxies.

"We've been wanting to do this for 14 years," said J. Xavier Prochaska, professor of astronomy and astrophysics at UC Santa Cruz, and coauthor of the paper. "The 'holy grail' has been to identify and study the galaxies that host the hydrogen gas we see in quasar spectra, and it took a facility with ALMA's capability to do it."

The galaxies, officially named ALMA J081740.86+135138.2 and ALMA J120110.26+211756.2, are each about 12 billion light-years from Earth.

With ALMA, the astronomers could observe the natural glow given off by carbon in the dense star-forming regions of the galaxies.

This emission was separated by a surprising distance from the gas spotted through quasar absorption, which means the galaxies are embedded in an extended halo of hydrogen gas.

"We had expected we would see faint emissions right on top of the quasar, and instead we saw bright galaxies at large separations from the quasar," said Prochaska.

"These galaxies appear to be massive, dusty, and rapidly star-forming systems, with large, extended layers of gas," Prochaska said. The galaxies are forming stars at more than 100 solar masses per year in one galaxy and about 25 solar masses per year in the other.

According to the researchers, the hydrogen gas revealed by its absorption of quasar light is most likely part of a large halo or perhaps an extended disk of gas around the galaxy.

"It's not where the star formation is, and to see so much gas that far from the star-forming region means there is a large amount of neutral hydrogen around the galaxy," Neeleman said.

The quasar is about 137,000 light-years from one galaxy and about 59,000 light-years from the other.

"ALMA has solved a decades-old question on galaxy formation," said Chris Carilli, an astronomer with the National Radio Astronomy Observatory in Socorro, and co-author on the paper.

"We now know that at least some very early galaxies have halos that are much more extended than previously considered, which may represent the future material for galaxy growth."

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