News

Solved! 40 Year-old Mystery on the Size of Shadowy Galaxies

Solved! 40 Year-old Mystery on the Size of Shadowy Galaxies

Credit: Adrian Malec (Swinburne University) and Marie Martig (Max Planck Institute for Astronomy, Heidelberg)

Artists impression of the power of background galaxies to measure the size of gas clouds as compared to the conventional method of using quasars. The plane to the far right shows the background galaxy and overlaid in the center of the galaxy is a bright white light representing a quasar. The DLA gas cloud is shown at the center of the plane in between the galaxy and Earth. The blue/white narrow beam indicates the small area of the DLA gas cloud probed by quasars, the wider red cone of light indicates the large area of the DLA probed by galaxies, which is a 100 million-fold increase in area.

MEDIA
Steve Jefferson
Communication Officer
W. M. Keck Observatory
sjefferson@keck.hawaii.edu

SCIENCE
Jeff Cooke
Swinburne University
jcooke@astro.swin.edu.au

John O’Meara
St. Michael’s College
jomeara@smcvt.edu

MAUNAKEA, Hawaii – Using the world’s largest telescopes, researchers discovered ancient cold gas clouds larger than galaxies in the early Universe. The discovery was announced today at a press conference at the 227th meeting of the American Astronomical Society in Orlando, Florida.

The discovery, led by Associate Professor Jeff Cooke, Swinburne University of Technology, and Associate Professor John O’Meara, St. Michael’s College, has helped solve a decades-old puzzle on the nature of gas clouds, known as damped Lyman alpha systems, or DLAs.

Cooke and O’Meara realized that finding DLA gas clouds in the line of sight to background galaxies would enable measurements of their size by determining how much of the galaxy they cover.

“Our new method first identifies galaxies that are more likely to have intervening DLA gas clouds and then searches for them using long, deep exposures on the powerful Keck Observatory 10m telescopes on Maunakea and deep data from the VLT 8m telescopes in Chile,” Cooke said. “The technique is timely as the next generation of giant 30m telescopes will be online in several years and are ideal to take advantage of this method to routinely gather large numbers of DLAs for study.”

DLA clouds contain most of the cool gas in the Universe and are predicted to contain enough gas to form most of the stars we see in galaxies around us today, like the Milky Way. However, this prediction has yet to be confirmed.

DLAs currently have little ongoing star formation, making them too dim to observe directly from their emitted light alone. Instead, they are detected when they happen to fall in the line of sight to a more distant bright object and leave an unmistakeable absorption signature in the background object’s light.

Previously, researchers used quasars as the background objects to search for DLAs. Although quasars can be very bright, they are rare and are comparatively small, only a fraction of a light year across, whereas galaxies are quite common and provide a 100 million-fold increase in area to probe DLAs.

“Using the galaxy technique, DLAs can be studied in large numbers to provide a 3-D tomographic picture of distribution of gas clouds in the early Universe and help complete our understanding of how galaxies formed and evolved over cosmic time,” O’Meara said.

The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes near the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrographs and world-leading laser guide star adaptive optics systems.

Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.