The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Overview and Early Data (1508.04473v2)

Abstract: The Extended Baryon Oscillation Spectroscopic Survey (eBOSS) will conduct novel cosmological observations using the BOSS spectrograph at Apache Point Observatory. Observations will be simultaneous with the Time Domain Spectroscopic Survey (TDSS) designed for variability studies and the Spectroscopic Identification of eROSITA Sources (SPIDERS) program designed for studies of X-ray sources. eBOSS will use four different tracers to measure the distance-redshift relation with baryon acoustic oscillations (BAO). Using more than 250,000 new, spectroscopically confirmed luminous red galaxies at a median redshift z=0.72, we project that eBOSS will yield measurements of $d_A(z)$ to an accuracy of 1.2% and measurements of H(z) to 2.1% when combined with the z>0.6 sample of BOSS galaxies. With ~195,000 new emission line galaxy redshifts, we expect BAO measurements of $d_A(z)$ to an accuracy of 3.1% and H(z) to 4.7% at an effective redshift of z= 0.87. A sample of more than 500,000 spectroscopically-confirmed quasars will provide the first BAO distance measurements over the redshift range 0.9<z\<2.2, with expected precision of 2.8% and 4.2% on $d_A(z)$ and H(z), respectively. Finally, with 60,000 new quasars and re-observation of 60,000 quasars known from BOSS, we will obtain new Lyman-alpha forest measurements at redshifts z\>2.1; these new data will enhance the precision of $d_A(z)$ and H(z) by a factor of 1.44 relative to BOSS. Furthermore, eBOSS will provide improved tests of General Relativity on cosmological scales through redshift-space distortion measurements, improved tests for non-Gaussianity in the primordial density field, and new constraints on the summed mass of all neutrino species. Here, we provide an overview of the cosmological goals, spectroscopic target sample, demonstration of spectral quality from early data, and projected cosmological constraints from eBOSS.

• The paper presents eBOSS’s main contribution by extending cosmological measurements using BAO and RSD techniques over a wide redshift range.
• It details a robust survey design that employs LRGs, ELGs, and quasars to achieve sub-percent precision in mapping large-scale structures.
• The study demonstrates improved constraints on dark energy models and neutrino masses by integrating eBOSS data with complementary observations like Planck.

Overview and Implications of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS)

The paper "The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Overview and Early Data" provides a comprehensive introduction to the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), a part of the Sloan Digital Sky Survey IV (SDSS-IV). This project is an ambitious spectroscopic survey that builds upon the success of the Baryon Oscillation Spectroscopic Survey (BOSS), expanding its capabilities and scientific reach. Through the utilization of the proven infrastructure and techniques of BOSS, eBOSS is designed to address fundamental questions in cosmology, particularly those pertaining to the nature of dark energy, the growth of large-scale structures, and the constraints on neutrino masses.

Scientific Objectives and Survey Design

eBOSS aims to deliver high-precision measurements of the cosmic distance scale and the growth of structure over an expansive redshift range from 0.6 to 2.2. The core scientific objective is to improve the constraints on the cosmological model by leveraging the power of Baryon Acoustic Oscillations (BAO) and Redshift Space Distortions (RSD) through an extensive spectroscopic survey.

The survey encompasses a systematic paper using over 7500 square degrees of celestial area, deploying four distinct tracers of large-scale structure: Luminous Red Galaxies (LRGs), Emission Line Galaxies (ELGs), quasars for direct clustering measurement, and high-redshift quasars for Lyα forest studies. Each tracer is carefully selected to optimize the mapping of the underlying matter distribution at various epochs in cosmic history.

• LRGs and ELGs: These targets serve to fill the redshift gap between previous SDSS galaxy samples and provide precise BAO measurements. LRGs are expected to enable sub-percent level precision on distance measurements up to z=1.
• Quasars: A comprehensive quasar sample targets both the direct clustering regime and higher redshift quasars for Lyα absorption studies, providing unique leverage on BAO and structure growth up to z=2.2.

Expected Results and Cosmological Implications

The strong statistical power of eBOSS is expected to substantively advance the understanding of the energy budget of the Universe, providing key insights into dark energy's role in cosmic acceleration. The projected precision in BAO measurements can distinguish between a cosmological constant and evolving dark energy models. By combining the survey data with Planck CMB measurements, eBOSS aims to constrain the dark energy equation-of-state parameters, $\omega_0$ and $\omega_a$, with substantially higher accuracy than current limits.

The survey's RSD observations are poised to probe potential deviations from General Relativity by mapping the growth of cosmic structures. eBOSS aims to measure the growth index $\gamma$ with unprecedented precision, testing models of modified gravity at cosmological scales.

Furthermore, eBOSS is well-placed to contribute to the field of neutrino physics. The precise clustering measurements of eBOSS can place compelling constraints on the sum of neutrino masses, with the potential to improve current limits significantly. The eBOSS dataset, combined with advances in theoretical modeling and simulation, will refine estimates of the broad-band power spectrum affected by massive neutrinos, thereby addressing questions fundamental to high-energy physics and cosmology.

Conclusion

The eBOSS represents a substantial step forward in the precision mapping of the Universe. By capturing the transitional epoch of $0.6