Free Astronomy Magazine May-June 2021

MAY-JUNE 2021 ready yielded more than a thousand new gravitational lenses, and there are undoubtedly many more await- ing discovery.” The DESI Legacy Imaging Surveys data are served to the astronomical community via the Astro Data Lab at NOIRLab’s Community Science and Data Center (CSDC). “Providing science-ready datasets for discovery and exploration is core to our mission,” said CSDC Director Adam Bolton. “The DESI Legacy Im- aging Surveys is a key resource that can be used for years to come by the astronomy community for investiga- tions like these.” To analyze the data, Huang and team used the National Energy Re- search Scientific Computer Center’s (NERSC) supercomputer at Berkeley Lab. “The DESI Legacy Imaging Sur- veys were absolutely crucial to this study; not just the telescopes, in- struments, and facilities but also data reduction and source extrac- tion, ” explains Huang. “The combi- nation of the breadth and depth of the observations is unparalleled.” With the huge amount of science- ready data to work through, the researchers turned to a kind of ma- chine learning known as a deep residual neural net. Neural nets are computing algorithms that are somewhat comparable to a human brain and are used for solving arti- ficial intelligence problems. Deep neural nets have many layers that collectively can decide whether a candidate object belongs to a par- ticular group. In order to be able to do this, however, the neural nets have to be trained to recognize the objects in question. With the large number of lens can- didates now on hand, researchers can make new measurements of cosmological parameters such as the Hubble constant. The key will be to detect a supernova in the back- ground galaxy, which, when lensed by a foreground galaxy, will appear as multiple points of light. Now that astronomers know which galaxies show evidence for strong lensing, they know where to search. New facilities such as the Vera C. Rubin Observatory (currently under construction in Chile and operated by NOIRLab) will monitor objects like these as part of its mission, al- lowing any supernova to be meas- ured rapidly by other telescopes. Undergraduate students played a significant role in the project from its beginning. University of Califor- nia student Andi Gu said, “My role on the project has helped me de- velop several skills which I believe to be key for my future academic career.” E xamples of gravitational lenses found in the DESI Legacy Survey data. [DESI Legacy Imaging Surveys/ LBNL/DOE & KPNO/CTIO/NOIRLab/ NSF/AURA] The lensing study was possible be- cause of the availability of science- ready data from the DESI Legacy Imaging Surveys, which were con- ducted to identify targets for DESI’s operations, and from which the ninth and final dataset has just been released. These surveys comprise a unique blend of three projects that have observed a third of the night sky: the Dark Energy Camera Legacy Survey (DECaLS), observed by the DOE-built Dark Energy Camera (DECam) on the Víctor M. Blanco 4- meter Telescope at CTIO in Chile; the Mayall z-band Legacy Survey (MzLS), by the Mosaic3 camera on the Nicholas U. Mayall 4-meter Tel- escope at KPNO; and the Beijing- Arizona Sky Survey (BASS) by the 90Prime camera on the Bok 2.3- meter Telescope, which is owned and operated by the University of Arizona and located at KPNO. “We designed the Legacy Surveys imaging project from the ground up as a public enterprise, so that it could be used by any scientist,” said study co-author Arjun Dey, from NSF’s NOIRLab. “Our survey has al- !