eBOSS

eBOSS is a cosmological spectroscopic survey conducted as part of Sloan Digital Sky Survey IV that mapped the large-scale structure of the Universe using optical spectroscopy of galaxies, quasars, and emission-line objects. It extended the redshift reach of prior SDSS programs to probe baryon acoustic oscillations (BAO), redshift-space distortions (RSD), and the expansion history from intermediate to high redshift. The survey built on the legacy of earlier projects at the Apache Point Observatory and contributed data products used by teams across Harvard–Smithsonian Center for Astrophysics, Lawrence Berkeley National Laboratory, and international partners including the Max Planck Institute for Astronomy.

Overview

eBOSS operated within the framework of Sloan Digital Sky Survey IV alongside other programs at the Apache Point Observatory and the Las Campanas Observatory affiliated efforts. The survey targeted several tracer populations, including luminous red galaxies used previously by Baryon Oscillation Spectroscopic Survey, emission-line galaxies similar to those in DEEP2 Redshift Survey, and quasars analogous to targets in the 2dF QSO Redshift Survey. eBOSS filled the redshift gap between low-redshift surveys like Sloan Digital Sky Survey I–III and high-redshift probes such as the Dark Energy Spectroscopic Instrument era, enabling cross-comparisons with results from the Planck cosmic microwave background analyses and constraints from the Dark Energy Survey.

Survey design and instrumentation

The observational program used the 2.5-meter Sloan Foundation Telescope at Apache Point Observatory equipped with multi-fiber spectrographs that were upgraded by teams at Lawrence Berkeley National Laboratory and University of Washington. Fiber targeting and tiling strategies built on algorithms developed for Sloan Digital Sky Survey I–III and incorporated lessons from Baryon Oscillation Spectroscopic Survey tiling and plate designs. Wavelength coverage and resolution specifications were set to permit reliable redshift measurements comparable to those achieved by the 2dF Galaxy Redshift Survey and the WiggleZ Dark Energy Survey. Instrument calibration and throughput monitoring involved collaboration with instrument groups at Carnegie Mellon University and engineering teams at Yale University.

Target selection and data processing

Target selection combined photometric catalogs from the Sloan Digital Sky Survey imaging pipeline with algorithms informed by studies from the Two Micron All Sky Survey and color selection techniques used in the Canada–France–Hawaii Telescope Legacy Survey. Quasar selection exploited variability analyses similar to those from the Palomar Transient Factory and color–magnitude cuts refined by teams linked to the University of Portsmouth. Fiber assignment and collision corrections followed statistical approaches developed in the Baryon Oscillation Spectroscopic Survey and the 2dFGRS collaborations. Data reduction and redshift fitting used spectral pipelines descended from the original SDSS spectroscopic reduction, with quality assessment by groups at the Max Planck Institute for Astronomy and cross-validation against catalogs from the Sloan Digital Sky Survey Data Release 12 era.

Scientific goals and key results

Primary goals included measurement of the BAO scale across multiple redshift bins to constrain the expansion history and dark energy models compared against predictions from Planck results and theoretical frameworks developed within the Lambda-CDM paradigm. Secondary aims encompassed RSD measurements to probe structure growth, tests of primordial non-Gaussianity complementary to analyses by the Atacama Cosmology Telescope and the South Pole Telescope, and legacy quasar science informing studies related to the Lyman-alpha forest exploited by earlier SDSS collaborations. Key results delivered percent-level BAO distance measurements consistent with Planck-based cosmology, improved growth-rate constraints that interfaced with results from the Dark Energy Survey and the Kilo-Degree Survey, and catalogs of millions of spectra enabling community investigations into galaxy evolution traced by comparisons to surveys like DEEP2, VVDS, and GAMA.

Data releases and access

Survey data products were made public through SDSS data releases, notably Sloan Digital Sky Survey Data Release 14 and Sloan Digital Sky Survey Data Release 16, with spectra, redshift catalogs, and value-added products accessible to the community. Data distribution mechanisms and documentation were coordinated with the broader SDSS collaboration including archival teams at Harvard–Smithsonian Center for Astrophysics and software contributions from groups at Carnegie Mellon University. The public releases facilitated cross-survey science with datasets from Planck, Dark Energy Survey, Gaia, and follow-up programs at observatories such as Keck Observatory and Subaru Telescope.

Category:Observational astronomy surveys