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HPC Software supports cosmic exploration

Teams of researchers from Argonne and Lawrence Berkeley national laboratories have developed cosmological simulation codes ready to translate streams of data observational data into new insights.

These codes will support Two new US Department of Energy-sponsored telescopes, the Dark Energy Spectroscopic Instrument (DESI) and the Vera C. Rubin Observatory, that wil be used to map cosmic structure in unprecedented detail.

Zarija Lukić, a computational cosmologist at LBNL’s Cosmology Computing Center states: “Our job is to provide the theoretical backdrop to these observations. You cannot infer much from observations alone about the structure of the universe without also having a set of powerful simulations producing predictions for different physical parameters.”

Lukić is a lead developer of Nyx, named after the Greek goddess of night. For more than a decade, the Nyx group has collaborated with the hardware/hybrid accelerated cosmology code, or HACC, team at Argonne, co-led by computational cosmologist Katrin Heitmann, who is also the principal investigator for an Office of Science SciDAC-5 project in High Energy Physics (HEP) that will continue to advance code development.

With a computing time grant from the ASCR Leadership Computing Challenge (ALCC), the Nyx and HACC teams are fine-tuning their codes, readying them to tease out cosmic details from incoming DESI and Rubin Observatory data.

The codes and telescopes focus on understanding how dark matter and dark energy shape cosmic structure and dynamics. Matter in the universe is unevenly distributed. Astronomers see a cosmic web, a vast tendril-like network of dense regions of gas and galaxies interspersed with low-density voids.

Heitmann’s HACC team collaborates closely with the Rubin Observatory’s Legacy Survey of Space and Time (LSST) observing campaign. Starting in early 2025, Rubin, in northern Chile, will record the entire visible southern sky every few days for a decade, tracking the movement of billions of galaxies in the low-redshift, or nearby, universe. This will produce unprecedented amounts of data: six million gigabytes per year.

“Our simulations are geared toward supporting the large observational surveys that are coming online,” says Heitmann, who’s also a spokesperson for LSST’s Dark Energy Science Collaboration. “They are large cosmic volume with very high resolution and there are only a handful of such stimulations currently available in the world.”

The Nyx team is working closely with DESI, which began collecting data in 2022. Located at the Kitt Peak Observatory in Arizona, DESI’s four-year spectroscopic observing campaign will map the cosmos’ large-scale structure across time using its 5,000-eye fibre-optic robotic telescope. It will observe about 30 million pre-selected galaxies and quasars across a third of the night sky.

As part of this, DESI will observe about 840,000 distant, or high redshift, quasars, three times as many as previous surveys collected. Quasars are astoundingly bright objects – thousands of times as bright as an entire galaxy. As their light travels between the quasar and Earth, some wavelengths are absorbed by neutral hydrogen gas present in the intergalactic medium between distant galaxies. Thus, the quasar’s distinctive light fingerprint, known as the Lyman-alpha forest, maps intergalactic hydrogen distribution.

The full story was originally published on the ASCR website.


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