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| LAMOST ExtraGAlactic Survey (LEGAS) | |
|---|---|
| Name | LAMOST ExtraGAlactic Survey (LEGAS) |
| Established | 2012 |
| Location | Xinglong Observatory |
LAMOST ExtraGAlactic Survey (LEGAS) is a wide-area spectroscopic survey of extragalactic objects conducted with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope. It complements imaging surveys and redshift programs by providing millions of spectra across the Northern Hemisphere, enabling studies of galaxy formation, large-scale structure, and active galactic nuclei. LEGAS operates in coordination with multiple observatories and survey projects to maximize scientific return and legacy value.
LEGAS is built around the Large Sky Area Multi-Object Fiber Spectroscopic Telescope at Xinglong Observatory and integrates observing strategies influenced by projects such as the Sloan Digital Sky Survey, 2dF Galaxy Redshift Survey, DEEP2 Redshift Survey, WISE, and Pan-STARRS. The survey targets galaxies, quasars, and emission-line objects across contiguous sky regions to map redshift-space structure and complement imaging from missions like GALEX, SDSS, UKIDSS, and DESI Legacy Imaging Surveys. LEGAS collaborates with institutions including the Chinese Academy of Sciences, Peking University, National Astronomical Observatories of China, and international partners linked to European Southern Observatory and National Astronomical Observatory of Japan.
Instrumentation centers on the 4-meter class LAMOST telescope with a 5-degree focal plane and 4,000 fiber positioning units, a concept comparable in multiplexing ambition to the Anglo-Australian Telescope with 2dF and the design lineage related to projects like Subaru Telescope instrumentation. Spectrographs provide low-resolution optical spectra suitable for redshift measurement, stellar population analysis, and emission-line diagnostics, drawing technical parallels to spectrographs used by Hobby-Eberly Telescope, Keck Observatory, and Very Large Telescope. The survey design incorporates tiling strategies akin to those developed for Baryon Oscillation Spectroscopic Survey and fiber-allocation algorithms used in Dark Energy Spectroscopic Instrument planning.
Target selection for LEGAS synthesizes photometric catalogs from SDSS, Pan-STARRS1, UKIDSS, WISE, and space-based surveys such as GALEX to identify candidate galaxies, active galactic nuclei, and emission-line objects, using color cuts and morphology criteria parallel to selection methods in eBOSS and VVDS. Observing strategies divide sky coverage into plates with prioritized target classes including luminous red galaxies, emission-line galaxies, and quasar candidates drawn from cross-matches with catalogs from 2MASS and FIRST. Scheduling accounts for seasonal visibility of fields near Beijing latitude and coordinates practicalities similar to those faced by LAMOST and by programs at Cerro Tololo Inter-American Observatory.
Raw spectra from LEGAS are processed through pipelines for bias subtraction, wavelength calibration, sky subtraction, and flux calibration, employing algorithms conceptually related to reductions used by SDSS and LAMOST LEGUE. Derived data products include redshift catalogs, spectral classifications, emission-line flux measurements, stellar population indices, and value-added catalogs that cross-match objects with external databases such as NED and SIMBAD. Data releases follow formats comparable to those of SDSS Data Release series and include FITS spectra, catalogs, and documentation to support cosmological analyses, galaxy evolution studies, and AGN demographics.
Primary goals encompass mapping the three-dimensional distribution of galaxies for large-scale structure studies, constraining galaxy formation and evolution through spectral indicators, and cataloging active galactic nuclei across a wide luminosity range; these goals align with scientific themes advanced by Lambda-CDM cosmology tests exemplified in analyses from Planck and WMAP. Key results include large redshift catalogs that improve measurements of galaxy clustering, identification of rare populations such as post-starburst galaxies and low-luminosity quasars akin to discoveries from SDSS and 2dFGRS, and contributions to studies of galaxy environments comparable to work from GAMA and COSMOS. LEGAS spectra have enabled emission-line diagnostic work building on the Baldwin–Phillips–Terlevich diagram tradition and have supported black hole mass estimates using techniques related to reverberation mapping applied in studies by Lick Observatory and Keck teams.
LEGAS operations involve collaborations among institutes including the National Astronomical Observatories of China, Peking University, Tsinghua University, and international research groups from institutions such as IAP, University of Cambridge, and Princeton University. Data release policies are structured to balance proprietary periods for survey teams with community access, following precedents set by SDSS and 2dFGRS where public data releases provide catalogs and spectra. Access mechanisms include online archives and query tools similar to the services offered by SDSS SkyServer and virtual observatory standards promoted by the International Virtual Observatory Alliance.
LEGAS legacy contributions are expected to include enduring spectroscopic catalogs that feed multi-wavelength studies across surveys like LSST, Euclid, WFIRST (now Roman Space Telescope), and DESI, serving as calibrators for photometric redshifts and training sets for machine-learning applications developed in collaboration with groups at Google DeepMind and university data-science centers. Future directions involve deeper or higher-resolution follow-up with facilities such as Subaru Telescope, Keck Observatory, and proposed multi-object spectrographs on 8–10 m class telescopes, as well as synergies with next-generation radio facilities like Square Kilometre Array and cosmic microwave background experiments tied to Planck heritage.
Category:Astronomical surveys Category:Observational astronomy Category:Large Sky Area Multi-Object Fiber Spectroscopic Telescope