The Extended Baryon Oscillation Spectroscopic Survey (eBOSS)
eBOSS will map the distribution of galaxies and quasars from when the Universe was 3 to 8 billion years old, a critical time when dark energy started to affect the expansion of the Universe. Image Credit: Dana Berry / SkyWorks Digital Inc. and the SDSS collaboration.
eBOSS will map the distribution of galaxies and quasars from when the Universe was 3 to 8 billion years old, a critical time when dark energy started to affect the expansion of the Universe. Image Credit: Dana Berry / SkyWorks Digital Inc. and the SDSS collaboration.

eBOSS will precisely measure the expansion history of the Universe throughout eighty percent of cosmic history, back to when the Universe was less than three billion years old, and improve constraints on the nature of dark energy. "Dark energy" refers to the observed phenomenon that the expansion of the Universe is currently accelerating, which is one of the most mysterious experimental results in modern physics.

eBOSS concentrates its efforts on the observation of galaxies and in particular quasars, in a range of distances (redshifts) currently left completely unexplored by other three-dimensional maps of large-scale structure in the Universe. In filling this gap, eBOSS will create the largest volume survey of the Universe to date. The figure to the right shows the region that will be newly mapped by the eBOSS project. This region corresponds to the epoch when the Universe was transitioning from deceleration due to the effects of gravity, to the current epoch of acceleration.

The combination of eBOSS with the SPIDERS X-ray selected sample of quasars, and the TDSS variability selected AGN sample, will create a unique window into the full population of quasars at all epochs to redshift z = 3.

Key Science Questions

  • How does the transition from deceleration to acceleration occur? Is it consistent with existing theories of dark energy?
  • How does structure grow during this epoch? Are there signs of violations of the general relativistic theory of gravity, which could be related to the acceleration?
  • Can we detect anomalies in the very largest scale clustering that could tell us about the earliest moments in the Universe's history?
  • Can we detect the effects of cosmic neutrinos, and thus pin down the neutrino mass scale?
  • What is the evolution of bright quasars of all luminosities out to redshift z = 3?

eBOSS Technical Details

  • Dark-time observations
  • July 2014 – February 2019
  • 1000 fibers per 7-square-degree plate
  • Wavelength: 360-1000 nm, resolution R~2000
  • 300,000 luminous red galaxies over 6,000 square degrees, 0.6 < z < 1.0
  • 175,000 emission line galaxies over 1,000 square degrees, 0.6 < z < 1.1
  • 500,000 quasars over 6,000 square degrees, 0.8 < z < 3.5
  • 1–2% distance measurements from baryon acoustic oscillations between 0.6 < z < 2.5


Principal Investigator
Kyle Dawson (University of Utah)
Deputy PI
Jean-Paul Kneib (EPFL)
Survey Scientist
Will Percival (University of Waterloo)
Catalog Scientist
Ashley Ross (The Ohio State University)
Targeting Coordinator
Jeremy Tinker (New York University)
Tiling Coordinator
Hee-Jong Seo (Ohio University)
Lead Data Scientist
Julian Bautista (University of Portsmouth)

eBOSS Data Management Plan

eBOSS Sub-programs

eBOSS Survey
Planned eBOSS coverage of the Universe

eBOSS also includes two subprograms to follow up on other types of objects: the Time-Domain Spectroscopic Survey (TDSS) for variable objects, and the SPectroscopic IDentification of ERosita Sources (SPIDERS) for X-ray sources.



Principal Investigators
Paul Green (SAO/CfA) and Scott Anderson (UW)
Acting Targeting Coordinator
Chelsea MacLeod (SAO/CfA)
Data Coordinator
John Ruan (UW)

The Time-Domain Spectroscopic Survey (TDSS) selects photometrically variable targets (especially from Pan-STARRS 1 and archival SDSS imaging) for spectroscopic follow-up. These targets include quasars and multiple classes of variable stars, some of which may reveal previously unidentified phenomena. By spectroscopically identifying the physical nature of 100,000 detected variables, TDSS will greatly enhance the power of these existing data sets to illuminate the physics of stars and quasars. Future photometric surveys (such as the Large Synoptic Survey Telescope) will leverage TDSS observations to classify their detections more robustly.

TDSS additionally devotes a number of fibers to both "few-epoch spectroscopy" (FES) and to "repeat quasar spectroscopy" (RQS), and these both study optical spectroscopic variability. FES emphasizes multi-epoch observations of selected special subclasses known or suspected to reveal spectral variability, such as double-peaked emission line quasars, broad-absorption line quasars, and dwarf carbon stars; RQS emphasizes in a less subclass biased way the multi-epoch spectroscopy of quasars across a broad range of redshift and luminosity.



Principal Investigators
Andrea Merloni and Kirpal Nandra (MPE)
AGN Survey Coordinator
Antonis Georgakakis (MPE)
Clusters Survey Coordinator
Nicolas Clerc (IRAP)
Targeting Coordinator
Tom Dwelly (MPE)
Data Coordinator
Johan Comparat (MPE)

The main goal of the SPectroscopic IDentfication of ERosita Sources (SPIDERS) survey is to provide a complete and homogeneous optical spectroscopic followup of X-ray sources (both point-like and extended) detected by eROSITA in its first year of survey operation, to begin in Spring 2018. Before then, the SPIDERS Survey will be executed in steps, corresponding to different (increasing) levels of allocated fiber density, with the shallower early phase dedicated to the follow-up of the only existing wide area homogeneous X-ray surveys. In particular, we will target all the ROSAT All-Sky Survey (RASS) sources still missing spectroscopic follow-up within the full eBOSS footprint, as well as the hard X-ray AGN from the shallow XMM-Newton Slew Survey. Detailed description of the target selection and links to value-added catalogs are available in the SPIDERS target selection page.

SPIDERS will follow-up clusters of galaxies selected by cross-correlating faint ROSAT sources with red-galaxy excess found in SDSS imaging in the range 0.1<z<0.6. These are the most massive and largest clusters in the X-ray sky, and represent a well-defined sample that can be used as a first stepping stone for cluster cosmology experiments via measurement of the growth of structure (with ~4,500 clusters, it will be by far the largest homogeneously X-ray selected sample with full spectroscopic followup). Once eROSITA data become available, we will be able to target additional ~1,500 fainter, smaller mass and higher redshift clusters. The better angular resolution of eROSITA over ROSAT, and the better energy resolution, implies we will be able to better characterize the X-ray/optical selection and provide competitive cosmological measurements of cosmic growth.

eBOSS/SPIDERS shall also obtain >30,000 spectra of ROSAT, XMM and eROSITA X-ray selected AGN, about 40% of which in common with eBOSS QSO program and the remaining unique SPIDERS AGN targets.  This spectroscopic X-ray selected sample will be ~2.5 times larger than the total number of X-ray AGN with spectroscopic redshift currently known, and about a factor 10 larger than any existing coherent, contiguous, well-defined, X-ray survey.