DESI early data release holds nearly two million objects

Date:
June 13, 2023
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
The first batch of data from the Dark Energy Spectroscopic
Instrument is now available for researchers to explore. Taken
during the experiment's 'survey validation' phase, the data include
distant galaxies and quasars as well as stars in our own Milky Way.


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FULL STORY ==========================================================================
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, with nearly 2
million objects for researchers to explore.

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. In
this period between turning the instrument on and beginning the official science run, researchers made sure their plan for using the telescope
would meet their science goals -- for example, by checking how long it
took to observe galaxies of different brightness, and by validating the selection of stars and galaxies to observe.

"The fact that DESI works so well, and that the amount of science-grade
data it took during survey validation is comparable to previous
completed sky surveys, is a monumental achievement," said Nathalie Palanque-Delabrouille, co- spokesperson for DESI and a scientist at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley
Lab), which manages the experiment.

"This milestone shows that DESI is a unique spectroscopic factory
whose data will not only allow the study of dark energy but will also
be coveted by the whole scientific community to address other topics,
such as dark matter, gravitational lensing, and galactic morphology."
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.

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.

"Survey validation was very important for DESI because it allowed us
-- before starting the main survey -- to adjust our selection of all
the objects, including stars, bright galaxies, luminous red galaxies,
emission line galaxies, and quasars," said Christophe Yeche, a scientist
with the French Alternative Energies and Atomic Energy Commission
(CEA) who co-leads the target selection group. "We've been able to
optimize our selection and confirm our observation strategy." 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. For example, the early
data release contains detailed images from some well-known areas of the
sky, such as the Hubble Deep Field.

"There are some well-trodden spots where we've drilled down into the
sky," said Stephen Bailey, a scientist at Berkeley Lab who leads data management for DESI.

"We've taken valuable spectroscopic images in areas that are of interest
to the rest of the community, and we're hoping that other people will take
this data and do additional science with it." Two interesting finds have already surfaced: Evidence of a mass migration of stars into the Andromeda galaxy, and incredibly distant quasars, the extremely bright and active supermassive black holes sometimes found at the center of galaxies.

"We observed some areas at very high depth. People have looked at that
data and discovered very high redshift quasars, which are still so rare
that basically any discovery of them is useful," said Anthony Kremin,
a postdoctoral researcher at Berkeley Lab who led the data processing
for the early data release. "Those high-redshift quasars are usually
found with very large telescopes, so the fact that DESI -- a smaller,
4-meter survey instrument - - could compete with those larger, dedicated observatories was an achievement we are pretty proud of and demonstrates
the exceptional throughput of the instrument." Survey validation was
also a chance to test the process of transforming raw data from DESI's
ten spectrometers (which split a galaxy's light into different colors)
into useful information.

"If you looked at them, the images coming directly from the camera would
look like nonsense -- like lines on a weird, fuzzy image," said Laurie
Stephey, a data architect at the National Energy Research Scientific
Computing Center (NERSC), the supercomputer that processes DESI's
data. "The magic happens in the processing and the software being able
to decode the data. It's exciting that we have the technology to make
that data accessible to the research community and that we can support
this big question of 'what is dark energy?'" DESI's early data was a
unique project for NERSC. All of the experiment's code, including the computational heavy lifting, is written in the programming language
Python rather than the traditional C++ or Fortran.

"That was the first time that using pure Python was shown to be a
feasible approach for a major experiment at NERSC, and since then,
Python has become increasingly common in our user workload," Stephey said.

The DESI early data release is now available to access for free through
NERSC.

There is plenty of data yet to come from the experiment. DESI is
currently two years into its five-year run and ahead of schedule on its
quest to collect more than 40 million redshifts. The survey has already catalogued more than 26 million astronomical objects in its science run,
and is adding more than a million per month.

DESI is supported by the DOE Office of Science and by the National
Energy Research Scientific Computing Center, a DOE Office of Science
user facility.

Additional support for DESI is provided by the U.S. National Science Foundation, the Science and Technologies Facilities Council of the
United Kingdom, the Gordon and Betty Moore Foundation, the Heising-Simons Foundation, the French Alternative Energies and Atomic Energy Commission
(CEA), the National Council of Science and Technology of Mexico, the
Ministry of Economy of Spain, and by the DESI member institutions.

Kitt Peak National Observatory is a program of NSF's NOIRLab.

The DESI collaboration is honored to be permitted to conduct scientific research on Iolkam Du'ag (Kitt Peak), a mountain with particular
significance to the Tohono O'odham Nation.

Further information: https://data.desi.lbl.gov/doc/papers/
* RELATED_TOPICS
o Space_&_Time
# Astrophysics # Galaxies # Dark_Matter # Astronomy #
Black_Holes # Cosmology # Space_Telescopes # Big_Bang
* RELATED_TERMS
o Quasar o Galaxy o Hubble_Deep_Field o Dark_matter o
Magellanic_Clouds o Globular_cluster o Milky_Way o Edwin_Hubble

========================================================================== Story Source: Materials provided by
DOE/Lawrence_Berkeley_National_Laboratory. Original written by Lauren
Biron. Note: Content may be edited for style and length.


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Link to news story: https://www.sciencedaily.com/releases/2023/06/230613110102.htm

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