Legacy Surveys

Legacy Surveys. The Legacy Surveys are a coordinated suite of wide-field astronomical imaging projects designed to create a comprehensive, multi-wavelength map of the sky. These surveys combine data from instruments like the Dark Energy Camera and telescopes at premier observatories including Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory. Their primary objective is to support cosmology research, particularly studies of dark energy and dark matter, while also providing a foundational dataset for a vast range of astrophysical investigations. The resulting public data releases have become essential resources for astronomers worldwide.

Overview

The Legacy Surveys represent a collaborative effort led by institutions such as the Lawrence Berkeley National Laboratory and involving partnerships with the National Science Foundation, the United States Department of Energy, and National Aeronautics and Space Administration. They systematically image large portions of the celestial sphere, primarily from sites in the Northern Hemisphere and Southern Hemisphere to achieve nearly full-sky coverage. Key components include the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys, which provide the photometric groundwork for the Dark Energy Spectroscopic Instrument project. These surveys build upon the legacy of earlier wide-field projects like the Sloan Digital Sky Survey and the Two Micron All-Sky Survey, but with greater depth, resolution, and area.

Notable Legacy Surveys

The project comprises several distinct but complementary imaging surveys. The Dark Energy Camera Legacy Survey utilizes the powerful Dark Energy Camera on the Blanco Telescope at Cerro Tololo Inter-American Observatory to map the southern sky. In the north, the Beijing-Arizona Sky Survey uses the Bok Telescope at Kitt Peak National Observatory, while the Mayall z-band Legacy Survey employs the Mosaic3 camera on the Mayall Telescope. Additional infrared data is contributed by the UKIRT Infrared Deep Sky Survey and the NASA Wide-field Infrared Survey Explorer mission. Together, they cover over 14,000 square degrees of extragalactic sky.

Scientific Goals and Impact

The foremost scientific driver is constraining the properties of dark energy by measuring baryon acoustic oscillations and the growth of large-scale structure through weak gravitational lensing. The data catalogs millions of galaxies to trace the cosmic web and support target selection for the Dark Energy Spectroscopic Instrument. Beyond cosmology, the surveys have enabled discoveries in Galactic archaeology, the study of Milky Way satellites and stellar streams, and the identification of distant quasars and transient phenomena like supernovae. They have also been critical for planning observations with the James Webb Space Telescope and the Nancy Grace Roman Space Telescope.

Data Products and Access

The collaboration releases processed data products publicly through portals like the Astro Data Lab at the Space Telescope Science Institute and the NASA/IPAC Infrared Science Archive. Key products include calibrated images, source catalogs containing photometry in optical (g, r, z) and infrared bands, and value-added catalogs with photometric redshifts. The data are served via interactive viewers and application programming interfaces, facilitating large-scale data mining. These resources have been integral to projects like the Galaxy Zoo citizen science initiative and numerous studies from the Hubble Space Telescope and ALMA communities.

Technological and Methodological Innovations

The surveys pioneered large-scale data processing pipelines to handle petabytes of imaging data, employing sophisticated techniques for astrometric calibration, photometric calibration, and image subtraction. Innovations include the use of Tractor, a forward-modeling photometry code, to perform deblending and measure fluxes in crowded fields. The integration of data from multiple telescopes and instruments, such as those at the Lowell Observatory and Palomar Observatory, required novel cross-calibration methods. These advancements in survey astronomy directly informed the data handling strategies for the Vera C. Rubin Observatory and its Legacy Survey of Space and Time.

Category:Astronomical surveys Category:Astronomy projects Category:Dark energy