Usually, seeing ordinary galaxies when they are in front of a quasar is difficult, because quasars are blazingly bright and a young galaxy is relatively faint, the researchers said in a statement. But using ALMA, the astronomers were able to see the infrared light from the galaxies' ionized carbon shining on its own, and also hydrogen silhouetted in the shine of the quasars. The carbon, which emits light at a wavelength of 158 micrometers (the far infrared), marked the structure of each galaxy, while emissions of infrared light from dust showed regions where stars were being born, according to the study.
The glowing carbon also offered another clue to the galaxies' structure, because its position was offset from the hydrogen gases that the astronomers initially saw, as revealed by the quasars' shine. That means that the galaxies' gases extend far from the dense carbon regions, suggesting each galaxy has a large halo of hydrogen encircling it, the researchers said.
Looking at the foreground objects that a shining background quasar could reveal, "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," J. Xavier Prochaska, an astrophysicist at the University of California, Santa Cruz, and co-author on the new study, said in a statement.
The data also showed that the young galaxies have already begun rotating, which is a hallmark of spiral galaxies like the Milky Way, the study said.
The effort to find such early stage galaxies began in 2003, when Prochaska first worked on the idea of using the spectra of quasars, the wavelengths of light they emit, to reveal those of galaxies in the foreground. Such arrangements are called damped Lyman-alpha systems, because the hydrogen gas blocks certain wavelengths of light from the quasar, revealing the gas's presence and extent.
"ALMA has solved a decades-old question on galaxy formation," Chris Carilli, an astronomer with the National Radio Astronomy Observatory in Socorro, New Mexico and a co-author of the new study, said in another statement. "We now know that at least some very early galaxies have halos that are much more extended than previously considered," he said, adding that these halos "may represent the future material for galaxy growth."
The new work was detailed Friday (March 24) in the journal Science.
Original story on Space.com.
Photo: Artist impression of a progenitor of Milky Way-like galaxy in the early universe with a background quasar shinning through a 'super halo' of hydrogen gas surrounding the galaxy.