The Extended Baryon Oscillation Spectroscopic Survey

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 cosmic expansion.

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 oldand improve constraints on the nature of dark energy. “Dark energy” refers the observed phenomenon that the expansion of the Universe is currently accelerating, which is the most mysterious experimental result in modern physics.

eBOSS will concentrate its efforts on observing faraway galaxies, quasars in particular, in a range of distances (redshifts, denoted by z) currently unexplored by other 3-D maps of large-scale structure in the Universe. In filling this gap, eBOSS will create the largest volume survey of the Universe to date.

eBOSS will also include 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.

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.

MPIA researchers have already created the primary algorithms to select quasars from imaging data, and are planning on using it to study the history of the intergalactic medium and large-scale structure in the distant Universe.

Planned eBOSS coverage of the Universe. The region to be newly explored by eBOSS corresponds to the epoch when the Universe was transitioning from deceleration due to the effects of gravity, to the current epoch of acceleration due to dark energy.

Key Science Questions

  • In cosmic history, 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?
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