BigBOSS: The Ground-Based Stage IV BAO ExperimentThis Response to the Decadal Survey is submitted by:The Lawrence Berkeley National Laboratory 1 Cyclotron Rd MS 50R-5032, Berkeley, CA 94720 David Schlegel, DJSchlegel@lbl.gov, 510-495-2595 Chris EXECUTIVE SUMMARYThe BigBOSS experiment is a proposed DOE-NSF Stage IV ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the growth of structure with an allsky galaxy redshift survey. The project is designed to unlock the mystery of dark energy using existing ground-based facilities operated by NOAO. A new 4000-fiber R=5000 spectrograph covering a 3-degree diameter field will measure BAO and redshift space distortions in the distribution of galaxies and hydrogen gas spanning redshifts from 0.2 < z < 3.5. The Dark Energy Task Force figure of merit (DETF FoM) for this experiment is expected to be equal to that of a JDEM mission for BAO with the lower risk and cost typical of a ground-based experiment. This project will enable an unprecedented multi-object spectroscopic capability for the U.S. community through an existing NOAO facility. The U.S. community would have access directly to this instrument/telescope combination, as well as access to the legacy archives that will be created by the BAO key project.The BigBOSS survey will target luminous red galaxies, emission line galaxies, and QSOs. This experiment builds upon the SDSS-III/BOSS project, reusing many aspects of the BOSS spectrograph and computing pipeline designs. The BigBOSS project is enabled by the impressive 3 degree diameter field of view of the 4-m Mayall telescope at KPNO. The focal plane of this telescope will be filled with an automated fiber-positioner capable of targeting 4000 objects simultaneously over a wavelength range from 340 nm to 1130 nm with resolution R=2300-6100. This carefully-designed instrument is capable of measuring redshifts to the brightest [OII] emitters to z=2 with a 4-m aperture. Assuming a majority allocation of the dark time and optimal observing conditions during 30% of all nights, and with approximately onehour exposures, over 5 million targets will be visited per year. We propose to operate for six years at KPNO and then move the instrument to CTIO, the Mayall sister telescope in the southern hemisphere, for a four year run commencing after the Dark Energy Survey (DES) program.The 30-million galaxy sample of BigBOSS-North provides precision baryon acoustic oscillation measurements over 14000 square degrees from 0.2 < z < 2.0 and a million QSOs from 1.8< z <3.5. A continuation with BigBOSS-South completes the survey, bringing the total to 50 million galaxies over 24000 square degrees. BigBOSS will sculpt the redshift distribution to maximize the statistical significance of the dark energy measurement. The target selection will be done using existing and planned imaging surveys. A summary of experiment goals is shown in Table 1.BigBOSS is proposed as a partnership between NSF/NOAO and DOE/OHEP. Details of this partnership will be determined w...

We report studies on the mitigation of optical effects of bright low-Earth-orbit (LEO) satellites on Vera C. Rubin Observatory and its Legacy Survey of Space and Time (LSST). These include options for pointing the telescope to avoid satellites, laboratory investigations of bright trails on the Rubin Observatory LSST camera sensors, algorithms for correcting image artifacts caused by bright trails, experiments on darkening SpaceX Starlink satellites, and ground-based follow-up observations. The original Starlink v0.9 satellites are g ∼ 4.5 mag, and the initial experiment “DarkSat” is g ∼ 6.1 mag. Future Starlink darkening plans may reach g ∼ 7 mag, a brightness level that enables nonlinear image artifact correction to well below background noise. However, the satellite trails will still exist at a signal-to-noise ratio ∼ 100, generating systematic errors that may impact data analysis and limit some science. For the Rubin Observatory 8.4 m mirror and a satellite at 550 km, the full width at half maximum of the trail is about 3″ as the result of an out-of-focus effect, which helps avoid saturation by decreasing the peak surface brightness of the trail. For 48,000 LEOsats of apparent magnitude 4.5, about 1% of pixels in LSST nautical twilight images would need to be masked.

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The Dark Energy Spectroscopic Instrument (DESI) embarked on an ambitious 5 yr survey in 2021 May to explore the nature of dark energy with spectroscopic measurements of 40 million galaxies and quasars. DESI will determine precise redshifts and employ the baryon acoustic oscillation method to measure distances from the nearby universe to beyond redshift z > 3.5, and employ redshift space distortions to measure the growth of structure and probe potential modifications to general relativity. We describe the significant instrumentation we developed to conduct the DESI survey. This includes: a wide-field, 3.°2 diameter prime-focus corrector; a focal plane system with 5020 fiber positioners on the 0.812 m diameter, aspheric focal surface; 10 continuous, high-efficiency fiber cable bundles that connect the focal plane to the spectrographs; and 10 identical spectrographs. Each spectrograph employs a pair of dichroics to split the light into three channels that together record the light from 360–980 nm with a spectral resolution that ranges from 2000–5000. We describe the science requirements, their connection to the technical requirements, the management of the project, and interfaces between subsystems. DESI was installed at the 4 m Mayall Telescope at Kitt Peak National Observatory and has achieved all of its performance goals. Some performance highlights include an rms positioner accuracy of better than 0.″1 and a median signal-to-noise ratio of 7 of the [O ii] doublet at 8 × 10−17 erg s−1 cm−2 in 1000 s for galaxies at z = 1.4–1.6. We conclude with additional highlights from the on-sky validation and commissioning, key successes, and lessons learned.

The Polarbear Cosmic Microwave Background (CMB) polarization experiment is currently observing from the Atacama Desert in Northern Chile. It will characterize the expected B-mode polarization due to gravitational lensing of the CMB, and search for the possible B-mode signature of inflationary gravitational waves. Its 250 mK focal plane detector array consists of 1,274 polarization-sensitive antenna-coupled bolometers, each with an associated lithographed band-defining filter. Each detector's planar antenna structure is coupled to the telescope's optical system through a contacting dielectric lenslet, an architecture unique in current CMB experiments. We present the initial characterization of this focal plane.