Large Scale Structure (LSS) surveys are designed to map the three-dimensional distribution of matter throughout the universe on cosmic scales. These low-redshift observations of galaxies, quasars (QSO's) and intergalactic gas (e.g. through the use of Lyα forest observations; Weinberg et al. 2003) assist with constraints on growth of structure, total matter content, and, if the survey volume is large enough, the expansion history of the universe. LSS surveys include 2dFGRS (2 degree Field Galaxy Redshift Survey; Colless et al. 2001), 6dFGS (6 degree Field Galaxy Survey; Jones et al. 2004) and WiggleZ (Blake et al. 2010).
Image Credit: NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz;
Called the eXtreme Deep Field, or XDF, the photo was assembled by combining 10 years of NASA Hubble Space Telescope photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field. The XDF is a small fraction of the angular diameter of the full moon. The Hubble Ultra Deep Field is an image of a small area of space in the constellation Fornax, created using Hubble Space Telescope data from 2003 and 2004. By collecting faint light over many hours of observation, it revealed thousands of galaxies, both nearby and very distant, making it the deepest image of the universe ever taken at that time. The new full-color XDF image is even more sensitive, and contains about 5,500 galaxies even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness of what the human eye can see.
A major survey is the Sloan Digital Sky Survey (SDSS) which began in 2000, but has continued over time as a phased series of subsequent surveys with additional instruments, such as the SDSS/BOSS (Baryon Oscillation Spectroscopic Survey). Analyses of LSS data extract matter power spectra, correlation functions, mass estimates from weak lensing (WL) and redshift space distortions (RSD) resulting from peculiar velocities of galaxies.
A slice through the SDSS 3-dimensional map of the distribution of galaxies. Earth is at the center, and each point represents a galaxy, typically containing about 100 billion stars. Galaxies are colored according to the ages of their stars, with the redder, more strongly clustered points showing galaxies that are made of older stars. The outer circle is at a distance of two billion light years. The region between the wedges was not mapped by the SDSS because dust in our own Galaxy obscures the view of the distant universe in these directions.
Contributed by the NASA / LAMBDA Archive Team.