Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe (1703.00052v2)

Abstract: We describe the Sloan Digital Sky Survey IV (SDSS-IV), a project encompassing three major spectroscopic programs. The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is observing hundreds of thousands of Milky Way stars at high resolution and high signal-to-noise ratio in the near-infrared. The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey is obtaining spatially-resolved spectroscopy for thousands of nearby galaxies (median redshift of z = 0.03). The extended Baryon Oscillation Spectroscopic Survey (eBOSS) is mapping the galaxy, quasar, and neutral gas distributions between redshifts z = 0.6 and 3.5 to constrain cosmology using baryon acoustic oscillations, redshift space distortions, and the shape of the power spectrum. Within eBOSS, we are conducting two major subprograms: the SPectroscopic IDentification of eROSITA Sources (SPIDERS), investigating X-ray AGN and galaxies in X-ray clusters, and the Time Domain Spectroscopic Survey (TDSS), obtaining spectra of variable sources. All programs use the 2.5-meter Sloan Foundation Telescope at Apache Point Observatory; observations there began in Summer 2014. APOGEE-2 also operates a second near-infrared spectrograph at the 2.5-meter du Pont Telescope at Las Campanas Observatory, with observations beginning in early 2017. Observations at both facilities are scheduled to continue through 2020. In keeping with previous SDSS policy, SDSS-IV provides regularly scheduled public data releases; the first one, Data Release 13, was made available in July 2016.

• The paper leverages APOGEE-2, MaNGA, and eBOSS to provide a comprehensive mapping of stars and galaxies.
• It employs high-resolution infrared spectra and integral field spectroscopy to analyze stellar populations and galactic dynamics.
• The findings constrain cosmic expansion and dark energy, setting the stage for future astronomical investigations.

Overview of the Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe

The Sloan Digital Sky Survey IV (SDSS-IV) is an ambitious astronomical project that significantly expands the scope of its predecessors to map both the local and distant universe through three major spectroscopic programs: APOGEE-2, MaNGA, and eBOSS. This initiative utilizes the 2.5 m Sloan Foundation Telescope at Apache Point Observatory and the 2.5 m du Pont Telescope at Las Campanas Observatory, enabling comprehensive observations across both hemispheres.

APOGEE-2: Galactic Archaeology

APOGEE-2 enhances our understanding of the Milky Way by gathering high-resolution, high signal-to-noise ratio infrared spectra of hundreds of thousands of stars, allowing for the analysis of their chemical and dynamical properties. This program builds upon APOGEE-1 by expanding sky coverage and the sheer volume of data, aiming to dissect the structure and evolution of the Milky Way. By targeting stars across the Galactic disk, bulge, and halo, including the Magellanic Clouds, APOGEE-2 provides insights into the history of stellar populations and Galactic dynamics.

MaNGA: Integral Field Spectroscopy of Nearby Galaxies

MaNGA is designed to paper the evolutionary processes of roughly 10,000 nearby galaxies through integral field spectroscopy. This enables two-dimensional mapping of stars and gas across these galaxies, facilitating the paper of star formation, chemical enrichment, and kinematic properties in unprecedented detail. MaNGA's unique capability to observe the spatial distribution of these properties allows researchers to probe fundamental questions about galaxy growth, stellar accretion, and the impact of environment on galaxy evolution.

eBOSS: Expanding the Cosmological Horizon

The extended Baryon Oscillation Spectroscopic Survey (eBOSS) pushes the boundaries of cosmological research by mapping the distribution of galaxies, quasars, and intergalactic gas over an unprecedented volume. eBOSS targets major gaps in the redshift range from 0.6 to 3.5, which is critical for understanding the transition from deceleration to acceleration in cosmic expansion. By employing baryon acoustic oscillations and redshift space distortions, eBOSS provides constraints on the universe's expansion history, dark energy, and modifications to general relativity.

Subprograms: SPIDERS and TDSS

Complementing eBOSS, the SPIDERS and TDSS programs further explore the universe's dynamic aspects. SPIDERS focuses on identifying X-ray detected active galactic nuclei (AGNs) and galaxy clusters, enhancing our comprehension of black hole accretion and its relationship with galaxies. TDSS, on the other hand, focuses on time-domain observations, targeting variable sources in the PS1 and SDSS catalogs to paper the underlying mechanisms driving such variability.

Data Management and Public Release

SDSS-IV continues the tradition of making significant contributions to the astronomical community through regular public data releases. These releases include reduced data, derived quantities, and value-added catalogs, ensuring transparency and facilitating further research. The data is meticulously archived and made accessible through advanced interfaces, optimizing for both academic and educational use.

Implications and Future Prospects

SDSS-IV serves as a foundational pillar for the next generation of astronomical research both in stellar and extragalactic studies. Its contributions to understanding the structure and dynamics of the Milky Way, the evolutionary history of galaxies, and the large-scale structure of the cosmos lay critical groundwork for future observatories and missions. As the survey progresses, it is anticipated that its findings will spur new theoretical developments and inspire observational strategies extending well beyond its operational timeline. The multi-faceted approach of SDSS-IV exemplifies its pivotal role in bridging the gap between current and future cosmic explorations.