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This timeline shows some pivotal events in the history of the Universe which is assumed to have begun with the Big Bang some 13.7 billion years ago (background article on age of the Universe here). The “Redshift Desert” is a region where the light from galaxies has been redshifted (stretched by the expansion of the Universe) into a region of the spectrum where a natural glow in the Earth's atmosphere interferes with key spectroscopic features of many of these galaxies. This interference is especially problematic when trying to study dimmer galaxies in the early Universe. Using a sophisticated observing technique that overcomes this problem, the Gemini Deep Deep Survey revealed that a large number of galaxies from this period of cosmic history were fully formed and more massive than the widely accepted Hierarchical Model of galaxy formation predicts.
This timeline also illustrates the concept of “look-back time,” which is what happens when astronomers look at more and more distant objects in space. Because light travels at a finite speed (about 300,000 km/s or 186,000 miles/s), it takes time for the light to reach our telescopes to be studied. This results in a cosmic “time-machine” because the light that we see from distant galaxies has traveled for billions of years. Thus, we see the galaxies as they were long ago when that light began its journey to our telescopes.
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Nearby Galaxies Illustrate the Power of the Gemini Deep Deep SurveyThis Canada-France-Hawaii Telescope image shows a small section of the nearby Virgo cluster of galaxies dominated by two giant elliptical galaxies on the left side of the image. The Gemini Deep Deep Survey (GDDS) studied much more distant galaxies than those shown in this image. However, the nearby elliptical galaxies in this image are thought to be older and even more massive, yet similar to some of the larger distant galaxies studied in the GDDS.Note the bright, smaller and bluer spiral galaxies on the right (center and bottom). These nearby spiral galaxies have active star formation occurring that makes them appear brighter and bluer. The limited number of galaxies observed spectroscopically in the redshift desert prior to the GDDS were mostly of this type. The GDDS allowed astronomers to thoroughly survey the more massive, redder yet dimmer galaxies as well. Light from galaxies in the nearby Virgo cluster has traveled for approximately 45 million years, whereas light from the galaxies studied in the GDDS has been traveling between 8-11 billion years to reach us.
Credit: “Canada-France-Hawaii Telescope/J.-C. Cuillandre/Coelum” |
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Why are some galaxies brighter than others?Bright galaxies where stars are forming may outshine dimmer, more massive galaxies. In all previous surveys of the “Redshift Desert,” the brighter star-forming galaxies were the only type bright enough to be sampled. The Gemini Deep Deep Survey was able to sample the dimmer, more massive galaxies and provide a better representation of the galaxies at this epoch of the Universe. The GDDS results revealed that there is a greater abundance of these more massive and older galaxies than expected from current models when the Universe was only 20-40% of its current age. Gemini Illustration by Jon Lomberg |
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What do apartment buildings and distant galaxies have in common?Observing older, massive galaxies in the “Redshift Desert” is similar to trying to determine the number of residents in an apartment building by counting the number of lit windows. In past surveys of this period of our Universe, mainly the brighter galaxies where stars are forming were bright enough to be studied. Prior to the Gemini Deep Deep Survey (GDDS), the more massive, older and fainter galaxies were not well represented in surveys of this epoch in the Universe––like the dark windows in the buildings above. The Gemini spectra from the GDDS allows us to study these dimmer galaxies and understand their properties such as mass, age and heavy element abundances.Gemini Illustration by Jon Lomberg |
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The Hierarchical TheoryArguably, the most widely accepted theory of galactic formation says that galaxies formed from “collisions” of smaller structures, which then evolved over the past 8-11 billion years into the galaxies we see today. This is called the “Hierarchical Theory”. The Gemini Deep Deep Survey brings into question key predictions of the Hierarchical Theory.Gemini Illustration by Jon Lomberg |
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Gemini North – Cloaked DomeThis “invisible dome” image of the Gemini North telescope was made by digitally “stacking” images of the open Gemini dome as it rotated. Approximately 40 individual 5-second exposures were stacked to produce the transparent dome effect, and one additional oneminute exposure was obtained of the sky following the dome rotation. Technical Notes: All images used a Nikon D1X camera with a 14mm f/2.8 Nikkor lens at an ISO setting of 800. Additional lighting was used inside the dome to illuminate the telescope and inside of the dome. (Note to photo editor: This image is also available in a landscape crop, but the sky is much less striking due to lack of bright Milky Way.)Gemini Observatory Photo by Peter Michaud & Kirk Pu`uohau-Pummill |
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Gemini North Interior by MoonlightA one-minute exposure of the interior of the Gemini North telescope by moonlight showing the 7story high telescope structure as well as the large wind vents for keeping the air inside the dome thermally stable.Gemini Observatory Photo by Peter Michaud |
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Gemini North with Southern Star-trailsApproximately 2 hours of stacked exposures of the summer sky over Gemini North. The setting moon provided light on right of dome and twilight provides a glow to the left side of dome, a small red light provides highlight on center of dome. . A star field has been offset by about 30 minutes to show individual stars separated from trails revealing Scorpius and Sagittarius over the Gemini dome. Technical Data: Each exposure was 50 seconds using a Nikon D1X camera and a 14mm f/2.8 Nikkor lens at an ISO setting of 800 and “stacked” in Photoshop to create the single image from the over 100 individual images.Gemini Observatory Photo by Peter Michaud & Kirk Pu`uohau-Pummill |
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