Mid-infrared photometry provides a robust technique for identifying active galaxies. While the ultraviolet to mid-infrared (k P 5 m) continuum of stellar populations is dominated by the composite blackbody curve and peaks at approximately 1.6 m, the ultraviolet to mid-infrared continuum of active galactic nuclei (AGNs) is dominated by a power law. Consequently, with a sufficient wavelength baseline, one can easily distinguish AGNs from stellar populations. Mirroring the tendency of AGNs to be bluer than galaxies in the ultraviolet, where galaxies (and stars) sample the blue, rising portion of stellar spectra, AGNs tend to be redder than galaxies in the mid-infrared, where galaxies sample the red, falling portion of the stellar spectra. We report on Spitzer Space Telescope mid-infrared colors, derived from the IRAC Shallow Survey, of nearly 10,000 spectroscopically identified sources from the AGN and Galaxy Evolution Survey. On the basis of this spectroscopic sample, we find that simple mid-infrared color criteria provide remarkably robust separation of active galaxies from normal galaxies and Galactic stars, with over 80% completeness and less than 20% contamination. Considering only broad-lined AGNs, these mid-infrared color criteria identify over 90% of spectroscopically identified quasars and Seyfert 1 galaxies. Applying these color criteria to the full imaging data set, we discuss the implied surface density of AGNs and find evidence for a large population of optically obscured active galaxies.

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We describe the Sloan

In a six-year program started in July 2014, the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) will conduct novel cosmological observations using the BOSS spectrograph at Apache Point Observatory. These observations will be conducted simultaneously 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. In particular, eBOSS will measure with percent-level precision the distance-redshift relation with baryon acoustic oscillations (BAO) in the clustering of matter. eBOSS will use four different tracers of the underlying matter density field to vastly expand the volume covered by BOSS and map the large-scale-structures over the relatively unconstrained redshift range 0.6 < z < 2.2. 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 the angular diameter distance 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 reobservation of 60,000 BOSS quasars, we will obtain new Lyα forest measurements at redshifts z > 2.1; these new data will enhance the precision of d A (z) and H(z) at z > 2.1 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 (RSD) 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. eBOSS 3 confidence, where w is the ratio of pressure to energy density for dark energy. Thus, current observations are generally consistent with the simplest picture where dark energy is described completely by Einstein's cosmological constant (Λ).New precise observations can unravel the origin of the accelerating universe; specifically, to determine if cosmic acceleration is caused by deviations in General Relativity (GR) on large scales or by a new form of (dark) energy. It is possible to decouple scenarios of acceleration that require dark energy from those that require modifications to GR by independently probing both cosmic expansion history and the structure growth rate. Four primary observational techniques are generally accepted as the most powerful toward obtaining that goal (e.g. Albrech...

This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library “MaStar”). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17).