Astronomers observe early stages of a Milky Way-like galaxy in the distant Universe

New observations reveal massive, dusty galaxies with high rates of star formation and large, extended layers of gas

EMBARGOED: Not for release until 11:30 p.m., IST, on Thursday, March 23.

Pune, India--

Observations of very distant Milky Way-like galaxies are important to understand the way galaxies formed in the Universe since the Big Bang. For decades, astronomers have found such distant galaxies indirectly by detecting the characteristic way their gas absorbs light from a bright quasar in the background because the galaxy is in eclipsing position between us and the quasar. Efforts to observe the light emitted by these galaxies have mostly been unsuccessful. Now, a team of astronomers using the Atacama Large Millimeter Array (ALMA) in Chile has, for the first time, observed ionized carbon emission from two such distant galaxies and the results were not what they had expected.

"For thirty years, we've been trying to identify the galaxies that show absorption against quasars, mostly without success. ALMA has opened a new window for such studies! But we expected to see faint carbon emission, from galaxies close to the quasar. We were astonished to find that the absorbers are actually very bright and large galaxies, quite distant from the quasar", said Nissim Kanekar, an associate professor at the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research (NCRA-TIFR), Pune, and a co-author of a paper on the new findings, published March 24 in Science.

The neutral hydrogen gas revealed by its absorption of the quasar light is most likely part of a large halo or extended disk of gas around the galaxy, said first author Marcel Neeleman, a post-doctoral fellow at the University of California (UC), Santa Cruz, California. "It's not where the stars are being formed, and to see so much gas that far from the star-forming region means there is a lot of neutral hydrogen around the galaxy," Neeleman said.

The researchers used ALMA to look for far-infrared carbon emission signatures from the galaxies, that they knew could be distinguished from the bright light of the quasars. They found both carbon and dust emission, indicating that the galaxies are forming stars very rapidly. The galaxies appearto be massive, dusty, and rapidly star-forming systems. Remarkably, at least one of them appears to be a rotating disk, like the Milky Way!

Kanekar mentioned that the ALMA results are just the beginning: the researchers are now working on new ALMA data on a much larger sample of galaxies that should shed more light on the characteristics of the absorber population.

Like NCRA-TIFR's Giant Metrewave Radio Telescope (GMRT), ALMA is a radio interferometer, which allows radio astronomers to make outstanding images of the sky. However, ALMA works at frequencies more than one hundred times larger than those of the GMRT, providing a completely different 
view of the Universe.

This research was supported by the National Science Foundation, USA, and the Department of Science and Technology, India.

Note to reporters: You may contact Nissim Kanekar at nkanekar@ncra.tifr.res.in (020-2571 9246) and Marcel Neeleman at marcel@ucsc.edu.