Extended Baryonic Oscillation Spectroscopic Survey (eBOSS)


The accelerating expansion of the Universe is the most surprising recent cosmological discovery, and led to the Nobel Prize in Physics in 2011. Pertaining to this acceleration, scientists have identified these top-level questions:

  1. Is this acceleration caused by a breakdown of General Relativity or by a new form of energy?
  2. If dark energy is causing the acceleration, is its energy density constant in space and time?

Measuring cosmic expansion and the growth of structure with high precision over a wide range of redshifts is the most effective way to address both questions. Doing so also addresses other questions: the mass of the neutrino and the nature of the inflationary epochs.

The extended-BOSS (eBOSS) project – one of the 3 surveys of the 4th generation Sloan Digital Sky Survey (SDSS-IV) – will create the largest volume three-dimensional map of the Universe ever made, addressing these questions in unexplored redshift regimes — including the epochs of transition from deceleration to acceleration.

Two major eBOSS subprograms will concurrently use ~10% of the fibers: the Time Domain Spectroscopic Survey (TDSS) and the Spectroscopic Identification of eROSITA Sources (SPIDERS). eBOSS, TDSS, and SPIDERS all include quasars as a major component, but select them very differently, yielding the largest and most complete spectroscopic survey of quasars ever created.

The eBOSS survey will start on September 2014 for a 6 year duration.

Prof. Jean-Paul Kneib of LASTRO is the Principal Investigator of eBOSS.

Cosmology and Large-Scale Structures

For the first time, eBOSS will enable high-precision distance measurements at epochs spanning the emergence of Dark Energy in the universe. Critically, the 1<z<2.2 expansion has never been probed using any method at comparable accuracy previously.

eBOSS will also provide new tests of General Relativity on cosmological scales through redshift-space distortions, new probes of inflation from limits on non-Gaussianity in the primordial density field, and new constraints on the summed mass of all neutrino species – possibly providing the first cosmological detection of the neutrino mass.

By targeting quasars and galaxies in the redshift window 0.6<z<3.5, eBOSS will produce the largest volume map of the Universe (covering approximately 11 Gpc3 and the strongest cosmological constraints to date from the baryon acoustic oscillation (BAO).

BAO yields cosmological distance measurements with low systematic errors, which the SDSS-III program BOSS has currently produced at high precision to z<0.6 and at z~2.3. Using the BOSS spectrographs, eBOSS targets luminous red galaxies between 0.6<z<0.8, emission lines galaxies between 0.6<z<1, quasars between 1<z<2.2, and Lyman-alpha quasars above z>2.2. We plan to obtain, respectively, 0.9%, 1.8%, 2.0% and 1.5% precision distances — greatly expanding the redshift range relative to BOSS, and doubling the accuracy of the BOSS measurements at the highest redshift using a denser set of Lyman-alpha forest quasars.