As the summer draws to a close, the UCI Center for Cosmology had a great opportunity to survey all the globally-leading research going on here. The Innovation News Network published an article surveying much of the research activity here. See a printable version at this link, or directly in the digital issue at this link.

Nearly 200 researchers, including Prof. David Kirkby’s research group from UCI’s Center for Cosmology, pitched in to gather, process, and stitch together images for half of the sky to prepare for the start of the Dark Energy Spectroscopic Instrument’s observations.

This video describes the monumental effort that went into constructing a 2D map of the universe to prepare for the Dark Energy Spectroscopic Instrument, which will produce the largest-ever 3D map of the universe. The final data release for the preparation of this 2D map, known as Data Release 9 or DR9, is scheduled to be distributed Jan. 13. (Credit: Marilyn Sargent/Lawrence Berkeley National Laboratory)

Before DESI, the Dark Energy Spectroscopic Instrument, can begin its 5-year mission from an Arizona mountaintop to produce the largest 3D sky map yet, researchers first needed an even bigger 2D map of the universe.

The 2D map, pieced together from 200,000 telescope images and several years of satellite data, lacks information about galaxy distances, and DESI will supply this and provide other useful details by measuring the color signatures and “redshift” of galaxies and quasars in its survey. Objects’ redder colors provide telltale information about their distance from Earth and about how quickly they are moving away from us – and this phenomenon is known as redshift.

In the end, this 2D map of the universe is the largest ever, based on the area of sky covered, its depth in imaging faint objects, and its more than 1 billion galaxy images.

The ambitious, 6-year effort to capture images and stitch them together for this 2D map – which involved 1,405 observing nights at three telescopes on two continents and years of data from a space satellite, an upgraded camera to image incredibly faint and distant galaxies, 150 observers and 50 other researchers from around the world. The effort also required 1 petabyte of data – enough to store 1 million movies – and 100 million CPU hours at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC).

2D map sets the stage for DESI observations, with a goal to solve dark energy mystery

“This is the biggest map by almost any measure,” said David Schlegel, co-project scientist for DESI who led the imaging project, known as the DESI Legacy Imaging Surveys. Schlegel is a cosmologist at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which is the lead institution for the international DESI collaboration.

The map covers half of the sky, and digitally sprawls over 10 trillion pixels, which is equivalent to a mosaic of 833,000 high-res smartphone photos. The DESI collaboration has about 600 participating scientists from 54 institutions around the world.

Publicly viewable at legacysurvey.org/viewer, the Sky Viewer map includes 2 billion objects – more than half of which are galaxies – and numerous clickable filters to select from specific object types or surveys. Some of the objects are individually labeled, and viewers can choose to display constellations, for example, and galaxies and quasars that will be imaged by DESI. Quasars are among the brightest objects in the universe, with supermassive black holes at their center that emit powerful jets of matter.

DESI is equipped with an array of 5,000 swiveling, automated robots, each toting a thin fiber-optic cable that will be pointed at individual objects. These cables will gather the light from 35 million galaxies and 2.4 million quasars during the five years of DESI observations.

DESI will collect and transmit data from these measurements to Berkeley Lab’s NERSC from Kitt Peak. Researchers at NERSC have already prepared for this incoming data by identifying which data-processing tasks would take up the most computing time and improving the code to speed up these tasks on the center’s current- and next-generation supercomputers. “In the end, we increased processing throughput five to seven times, which was a big accomplishment – bigger than I expected,” said Laurie Stephey, a data analytics engineer at NERSC who played a key role in the effort.

The primary purpose of compiling the 2D map data is to identify these galaxy and quasar targets for DESI, which will measure their light to pinpoint their redshift and distance. This will ultimately provide new details about mysterious dark energy that is driving the universe’s accelerating expansion.

Nathalie Palanque-Delabrouille, DESI co-spokesperson and a cosmologist at the French Alternative Energies and Atomic Energy Commission (CEA), noted that the expansion rate has evolved, and there are many unanswered questions about the changes in this rate.

“Our universe had a surprising history,” she explained. “During the first half of its life, its expansion was driven mostly by the dark matter it contains.” Dark matter is unknown matter, making up 85 percent of all matter in the universe and so far only observed indirectly through its gravitational effects on normal matter.

“However, in the past 7 billion years the expansion of our universe has been gradually accelerating under the influence of a mysterious dark energy,” she added, “and the goal of DESI is to precisely clarify this overall picture by unveiling what dark energy is.”

Palanque-Delabrouille has been involved in the effort to pick targets for DESI to observe from the surveys’ data. She noted that DESI will gather light from a mix of galaxies at several distances, including bright galaxies that are within 4 billion light years of Earth, so-called red galaxies that allow us to see back to 8 billion years ago, very young blue galaxies or “emission-line” galaxies that will go further back 10 billion years ago, and ultimately quasars, which are so bright they can be seen up to 12 billion light-years away.

“Having managed to collect and process these imaging data is really a major achievement. DESI wouldn’t be getting anywhere without such large imaging surveys,” she said.

via JPL