announcements

In its quest to study the effect of dark energy on the expansion history of the Universe, DESI has been charting the cosmos, creating the largest 3D map of the Universe ever made — a map that stretches back over 11 billion years of cosmic time.

In a press announcement today, the project made its initial report on the cosmological clues recorded in the map. The results make use of data from the first year of the DESI survey, which will be carried out over a total of five years.

DESI’s 3D map tracks the frozen-in imprint of baryon acoustic oscillations (BAO), as recorded two ways: in the spatial distributions of galaxies, and in the structure of intergalactic gas seen along the line of sight to distant quasars (the Lyman alpha forest). Using these data, DESI scientists have measured the BAO signal at 7 epochs (i.e., slices of cosmic time) from 3 billion to 11 billion years ago. Because the measured BAO signal is a so-called “standard ruler”, the scientists can infer how the Universe expanded over its history.

The results are amazingly precise. Because of DESI’s high efficiency and stability, combined with its ability to measure spectra for large numbers of galaxies and quasars, the Universe’s expansion history is now known to better than 1% precision, yielding the best picture yet of how the universe has evolved.

The results are in general agreement with the current best cosmological model (Lambda CDM), which takes into account the roles of dark energy and dark matter. But as noted by DESI Director Michael Levi, “we’re also seeing some potentially interesting differences that could indicate that dark energy is evolving over time. Those may or may not go away with more data, so we’re excited to start analyzing our three-year dataset soon.”

These results were reported in multiple papers posted on arXiv and in talks presented today at the American Physical Society meeting. A guide to the suite of papers presenting these results is available at the DESI blog.

The DESI Legacy Imaging Surveys team is pleased to announce the public release of the Siena Galaxy Atlas 2020 (SGA-2020), a value-added supplemental catalog to imaging Data Release 9 (DR9).

The SGA-2020 is a multiwavelength atlas of 383,620 nearby galaxies selected over the 20,000 square-degree imaging footprint based on their (large) apparent angular diameter. It has been used in Survey Validation and the Main Survey to improve the selection of BGS targets, for improved masking of faint, dark-time (ELG, LRG, QSO) targets, in secondary target programs (e.g., to facilitate studies of the peculiar velocity field in the local volume via the Tully-Fisher and Faber-Jackson relations), and more. Read more about the SGA-2020 on the AAS poster.

For each galaxy in the SGA, we carry out the following measurements:

• We generate custom grz and W1W2 image stacks using all the available imaging (upper-left panel);
• We use The Tractor, in the context of the legacypipe photometric pipeline to build a model of all the sources in the field (middle-left panel);
• We subtract all the sources in the field except the object of interest from the data and measure the surface-brightness profile using nested, fixed-geometry elliptical isophotes (bottom-left panel).

This procedure yields the non-parametric grz surface-brightness profiles, g-r and r-z color-radius profiles, and grz curves of growth shown in the right-hand panels of the figure above, and more.

Documentation of the SGA-2020 can be found here. A queryable web-application is also available here.

The ninth and final data release from the ambitious DESI Legacy Imaging Surveys was announced at the January (14th) 2021 meeting of the American Astronomical Society. This major milestone sets the stage for the start of the 5-year survey with the Dark Energy Spectroscopic Instrument (DESI), which aims to provide new insights into the nature of dark energy. See the NOIRLab organization release.

Using machine learning trained on real data, and applied on DESI Legacy Imaging Surveys Data Release 8th has uncovered the 1210 new strong lens candidates, approximately the double of known lenses. This research was presented in the paper Discovering New Strong Gravitational Lenses in the DESI Legacy Imaging Surveys to appear in The Astrophysical Journal. These new lens candidates can be used to make new measurements of cosmological parameters. See the Science Release Note.

The team behind this discovery is formed by of X. Huang (Department of Physics and Astronomy, University of San Francisco), C. Storfer (Department of Physics and Astronomy, University of San Francisco), A. Gu (Department of Physics, University of California, Berkeley), V. Ravi (Department of Computer Science, University of San Francisco), A. Pilon (Department of Physics and Astronomy, University of San Francisco), W. Sheu (Department of Physics, University of California, Berkeley), R. Venguswamy (Department of Physics, University of California, Berkeley), S. Banka (Department of Physics, University of California, Berkeley), A. Dey (NSF’s NOIRLab), M. Landriau (Physics Division, Lawrence Berkeley National Laboratory), D. Lang (Physics Division, Lawrence Berkeley National Laboratory; Department of Astronomy & Astrophysics, University of Toronto; Perimeter Institute for Theoretical Physics, Waterloo), A. Meisner (NSF’s NOIRLab), J. Moustakas (Department of Physics and Astronomy, Siena College), A. D. Myers (Department of Physics & Astronomy, University of Wyoming), R. Sajith (Department of Physics, University of California, Berkeley), E. F. Schlafly (NSF’s NOIRLab), and D. J. Schlegel (Physics Division, Lawrence Berkeley National Laboratory).

On May 8, 2020, the DOE Energy Systems Acquisition Advisory Board (ESAAB) approved the CD-4 completion of construction for the DESI Project. It’s the culmination of 10 years of hard work by an incredibly dedicated and talented team and a major accomplishment for all involved. DESI is now the premier multi-object spectrograph and the first stage-IV dark energy experiment to go on-sky.

DESI commissioning has raced forward this winter, and we have now
demonstrated the key performance parameters of the instrument!
Since installation of the instrument, refinement of the performance of the 8 square
degree corrector, high-precision (10 micron) positioning of the
fibers under active feedback, accurate calibration of the spectrographs,
and on-sky commissioning of the whole user interface have been demonstrated.

All of this progress culminated in successful demonstration in March
of spectroscopy with the full DESI system of many tens of thousands
of survey targets. The image below is of a luminous red galaxy targets, easily revealing the distinctive Balmer-line signature of a post-starburst galaxy at redshift 1.286! See our blog for more details!

Due to growing travel restrictions and concerns regarding the COVID-19 outbreak, the DESI2020 Collaboration Meeting, originally scheduled for March 9-12 in Tucson, AZ, was held completely remotely. The online format of the meeting was very successful and many important discussions centered on early data from commissioning and preparing for the upcoming Survey Validation.

The picture shows a small group of collaboration members that were “stranded” in Tucson before travel restrictions were put in place. They practiced social distancing in the Sonoran Desert!

DESI Opens It’s 5,000 Eyes to Capture the Colors of the Cosmos!
Full press release here

The completed 6-lens corrector, weighing in at 8,900 pounds, will deliver a huge 8-square degree field-of-view. That’s a sixteen times larger field-of-view than the previous optics. The six hexapods bolted to the skirt will actively position the corrector to microns accuracy.