SDSS-III, the third phase of the Sloan Digital Sky Survey, will produce unprecedented spectroscopic data sets for studying the matter and energy contents of the universe, cosmological initial conditions, and the physics of galaxy formation. This project covers theoretical research targeted at two of the four SDSS-III surveys: BOSS, the Baryon Oscillation Spectroscopic Survey, which will measure redshifts of one-and-a-half million luminous galaxies and Lyman-alpha forest spectra of a hundred and fifty thousand quasars, and APOGEE, the Apache Point Observatory Galactic Evolution Experiment, which will measure high-resolution near-infrared spectra of a hundred thousand stars from all regions of the Milky Way.
The high density of quasar sightlines in BOSS enables a three-dimensional treatment of the Lyman-alpha forest on large scales. Dr. Weinberg and collaborators will use analytic models to investigate the sensitivity of cross-sightline flux statistics to cosmological parameters. They will devise numerical methods to predict these statistics with the accuracy demanded by high-precision data, and they will investigate possible signatures of Helium-II reionization that might be detectable in the 3-D forest or in measurements of close quasar pairs. The team will apply halo occupation distribution (HOD) modeling to BOSS galaxy maps to infer the growth and merger history of luminous galaxies. They will use HOD-based methods to sharpen the cosmological constraints from BOSS.
For the APOGEE data, the research team will construct predictive models that combine chemical evolution prescriptions with numerical simulations of disk galaxy formation in a cold dark matter universe, and combine them with APOGEE's revolutionary data set of detailed observations of the Milky Way, to test galaxy formation theory. A variety of simulations, including disks evolved in isolation, disks perturbed by dark matter subhalos and merging satellites, and hydrodynamic simulations, will enable the research group to isolate different physical effects.
SDSS-III will have an enormous impact within the astronomical community and beyond, by creating public data archives that enable a broad range of scientific investigations and educational activities. By enhancing his scientific involvement with SDSS-III, this research will support Dr. Weinberg's role as the SDSS-III Project Scientist, working with the science teams of the four surveys to ensure that they produce high-quality data sets. Dr. Weinberg will also continue his multi-year collaboration with Macarthur Award winning artist Josiah McElheny to use cosmologically inspired sculptures as a basis for public outreach aimed at science- and art-oriented audiences.
Over the past 15 years, the Sloan Digital Sky Survey (SDSS) has carried out the largest ever surveys of structure in the universe and the populations of stars in the Milky Way galaxy. This grant's Principal Investigator (PI), David Weinberg, was the Project Scientist for the third phase of the SDSS, which carried out observations from 2008-2014 and published its final data release in January 2015. The grant supported theoretical research by Dr. Weinberg and his students that developed new methods for interpreting results from SDSS-III and future surveys, as well as applications of these methods to SDSS data. The results of this research were presented in more than 20 articles published in refereed scientific journals and in several public reports. The grant also supported Dr. Weinberg's collaboration with MacArthur Award-winning artist Josiah McElheny on the design of sculptures inspired by the discoveries of modern cosmology, which have been exhibited in museums and galleries across the United States and Europe. The most startling cosmological discovery of recent decades is that the expansion of the universe is speeding up over time rather than slowing down. We know gravity as an attractive force that holds objects to the earth, holds planets in orbit around the sun, and holds stars in orbit within the Milky Way. Over distances of billions of light years, however, it appears that the action of gravity is repulsive, accelerating distant galaxies away from each other. Understanding this mystery is one of the central goals of contemporary cosmology, including the largest of the SDSS-III surveys. One product of this grant is a book-length article titled "Observational Probes of Cosmic Acceleration" that reviews the techniques astronomers are using to measure the history of the expansion and growth of structure in the universe, methods that underpin SDSS-III and many of the most ambitious cosmological experiments planned for the coming decade. Dr. Weinberg and his collaborators also developed new methods for testing theories of cosmological gravity and cosmic acceleration using the motions of galaxies and the absorption of light by intergalactic hydrogen gas, and they applied these techniques to data from the SDSS and other surveys. SDSS-III has yielded the most precise measurements ever of the absolute distance scale of the cosmos. Dr. Weinberg has also been deeply involved in planning for the Wide Field Infrared Survey Telescope (WFIRST), planned to be NASA's major new astrophysics mission of the 2020s, which will apply SDSS-like techniques to map the more distant universe using the unique capabilities of a space-based platform. Another large SDSS-III survey, called APOGEE, has mapped the distribution of chemical elements in 100,000 stars in all regions of the Milky Way. Because the nuclei of atoms are themselves forged in the fusion furnaces of stellar interiors, the chemical fingerprint of a star encodes information about all the generations of stars that preceded it. Supported by this grant, Dr. Weinberg and his students developed a new statistical approach to classifying these chemical fingerprints, and they are now in the process of applying it to the APOGEE maps. They also used supercomputer simulations to develop a theoretical understanding how the disk of the Milky Way formed, showing that it may have started as a thick disk stirred by turbulence powered by vigorous star formation, and only gradually settled into the thin, ordered disk that the sun resides in. Dr. Weinberg's collaboration with Josiah McElheny on cosmological sculptures began in 2004, a series of works culminating in the installation "Island Universe." During the period of this grant, they collaborated on a new sculpture inspired by SDSS observations, a metal-and-glass "core sample" of the universe titled "Study for The Center is Everywhere." These sculptures were exhibited at White Cube Gallery in London, the Reina Sofia Museum in Madrid, and the Institute of Contemporary Art in Boston. Dr. Weinberg gave numerous popular lectures on these sculptures, which provide an ideal vehicle for bringing the ideas of modern cosmology to a broad cross section of the public.
