DESI Early Data Release Holds Nearly Two Million Objects

The first batch of data from the Dark Energy Spectroscopic Instrument is now available for researchers to mine. Taken during the experiment’s “survey validation” phase, the data include distant galaxies and quasars as well as stars in our own Milky Way 

The universe is big, and it’s getting bigger. To study dark energy, the mysterious force behind the accelerating expansion of our universe, scientists are using the Dark Energy Spectroscopic Instrument (DESI) to map more than 40 million galaxies, quasars, and stars. Today, the collaboration publicly released its first batch of data (see press release).   The 80-terabyte data set comes from 2,480 exposures taken over six months during the experiment’s “survey validation” phase in 2020 and 2021 and contains nearly 2 million objects for researchers to explore. 

Part of DESI’s survey validation included the “One-Percent Survey” visualized in this flythrough. Researchers took detailed images in 20 different directions on the sky, creating a 3D map of 700,000 objects and covering roughly 1% of the total volume DESI will study. With the instrument and survey plan successfully tested, the main DESI survey is now filling in the gaps between those observations. Credit: David Kirkby/DESI collaboration

Today, the collaboration also published a set of papers related to the early data release, which include early measurements of galaxy clustering, studies of rare objects, and descriptions of the instrument and survey operations. The new papers build on DESI's first measurement of the cosmological distance scale that was published in April, which used the first two months of routine survey data (not included in the early data release) and also showed DESI’s ability to accomplish its design goals.

WCA Postdoctoral Fellow, Enrique Paillas, is involved in the Galaxy & Quasar Clustering group in DESI, where he is helping to assess the robustness of the methods that DESI uses to measure the expansion history of the Universe, through the detection of baryon acoustic oscillations (BAO). These correspond to ripples that were imprinted in the distribution of galaxies from the very early Universe.  He also co-leads a subgroup within DESI, which focuses on studying new statistical methods to extract information from the galaxy maps that the survey will observe.

Enrique is a co-author on the early data release paper, and says:

DESI uses 5,000 robotic positioners to move optical fibers that capture light from objects millions or billions of light-years away. It is the most powerful multi-object survey spectrograph in the world, able to measure light from more than 100,000 galaxies in one night. That light tells researchers how far away an object is, building a 3D cosmic map. 

DESI uses 5,000 fiber-optic “eyes” to rapidly collect light from distant galaxies. In good observing conditions, the experiment can image a new set of 5,000 objects every 20 minutes. Credit: Marilyn Sargent/Berkeley Lab

Perimeter Institute Computational Scientist and Associate WCA member, Dustin Lang, was heavily involved in the imaging surveys; the 2-d maps of stars and galaxies that DESI picked its targets from, and then determined 3-d distances for.  Dustin is responsible for the interactive sky viewer, that will allow people around the world to zoom around the sky and investigate the newly released DESI spectra themselves.

As the universe expands, it stretches light’s wavelength, making it redder – a characteristic known as redshift. The further away the galaxy, the bigger the redshift. DESI specializes in collecting redshifts that can then be used to solve some of astrophysics’ biggest puzzles: what dark energy is and how it has changed throughout the universe’s history.

While DESI’s primary goal is understanding dark energy, much of the data can also be used in other astronomical studies.  WCA ATMD Postdoctoral Fellow, Alex Krolewski, is involved in mitigating redshift systematics for DESI clustering catalogs, and co-leads the topical group studying the combination of DESI data with the cosmic microwave background (CMB), in particular, its lensing and scattering by large-scale structure. He has been studying the large-scale clustering of DESI quasar targets using their gravitational lensing of the CMB.

WCA Postdoctoral Fellow, Shahab Joudaki, says, “DESI is the most powerful spectroscopic survey in the world.”  Shahab works on the combined analysis of DESI and the most powerful imaging surveys, which are complementary to one another and will together allow us to provide the most robust constraints on the underlying cosmology of the Universe. He is specifically focused on how we can account for their joint measurement uncertainties and the cosmological parameter inference.

 Shahab also directly contributes to the observing of DESI data.