Galaxies congregate in clusters and along filaments, and are missing from large regions referred to as voids. These structures are seen in maps derived from spectroscopic surveys1,2 that reveal networks of structure that are interconnected with no clear boundaries. Extended regions with a high concentration of galaxies are called ‘superclusters’, although this term is not precise. There is, however, another way to analyse the structure. If the distance to each galaxy from Earth is directly measured, then the peculiar velocity can be derived from the subtraction of the mean cosmic expansion, the product of distance times the Hubble constant, from observed velocity. The peculiar velocity is the line-of-sight departure from the cosmic expansion and arises from gravitational perturbations; a map of peculiar velocities can be translated into a map of the distribution of matter3. Here we report a map of structure made using a catalogue of peculiar velocities. We find locations where peculiar velocity flows diverge, as water does at watershed divides, and we trace the surface of divergent points that surrounds us. Within the volume enclosed by this surface, the motions of galaxies are inward after removal of the mean cosmic expansion and long range flows. We define a supercluster to be the volume within such a surface, and so we are defining the extent of our home supercluster, which we call Laniakea.
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We thank our many collaborators in the accumulation of Cosmicflows-2 distances. We thank the CLUES collaboration, and in particular S. Gottlöber and J. Sorce in connection with the analysis. T. Jarrett provided an unpublished 2MASS Extended Source Catalog redshift compendium, the only all-sky redshift catalogue extensive enough to match the region of our reconstruction. The narration in the Supplementary Video is by S. Anvar and the original music is played by N.-E. Pomarède. The name ‘Laniakea’ was suggested by N. Napoleon, Kapiolani Community College, Hawaii. Financial support was provided by US National Science Foundation award AST09-08846, several awards through the Space Telescope Science Institute for observing time with Hubble Space Telescope, an award from the Jet Propulsion Lab for observations with Spitzer Space Telescope, and NASA award NNX12AE70G for analysis of data from the Wide-field Infrared Survey Explorer. We also acknowledge support from the Israel Science Foundation (1013/12) and the Lyon Institute of Origins under grant ANR-10-LABX-66 and the CNRS under PICS-06233.
Extended data figures
By steps, the video illustrates the observed local distribution of galaxies, the observed departures from the expansion of the universe of the fraction of the galaxies with distance measurements, the inferred three-dimensional flow pattern of the local galaxies, and the inferred underlying distribution of matter causing these flows. Flows are differentiated between motions inward toward a local basin of attraction and flows outward toward external attractors. A boundary is located between inward and outward flows. We call the contiguous region of the inward flow pattern the Laniakea Supercluster of galaxies, our home supercluster. For a high resolution version of this video please follow this link http://irfu.cea.fr/laniakea or http://vimeo.com/pomarede/laniakea.