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Dark matter maps reveal cosmic scaffolding


Ordinary baryonic particles (such as protons and neutrons) account for only one-sixth of the total matter in the Universe1,2,3. The remainder is a mysterious ‘dark matter’ component, which does not interact via electromagnetism and thus neither emits nor reflects light. As dark matter cannot be seen directly using traditional observations, very little is currently known about its properties. It does interact via gravity, and is most effectively probed through gravitational lensing: the deflection of light from distant galaxies by the gravitational attraction of foreground mass concentrations4,5. This is a purely geometrical effect that is free of astrophysical assumptions and sensitive to all matter—whether baryonic or dark6,7. Here we show high-fidelity maps of the large-scale distribution of dark matter, resolved in both angle and depth. We find a loose network of filaments, growing over time, which intersect in massive structures at the locations of clusters of galaxies. Our results are consistent with predictions of gravitationally induced structure formation8,9, in which the initial, smooth distribution of dark matter collapses into filaments then into clusters, forming a gravitational scaffold into which gas can accumulate, and stars can be built10.

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Figure 1: Map of the dark matter distribution in the two-square-degrees COSMOS field.
Figure 2: Sensitivity of probes of large-scale structure, as a function of distance.
Figure 3: Comparison of baryonic and non-baryonic large-scale structure.
Figure 4: Growth of large-scale structure.
Figure 5: Three-dimensional reconstruction of the dark matter distribution.

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This work was based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA). We also used data collected from: the XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and NASA; the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the European Southern Observatory, Chile; the Kitt Peak National Observatory, the Cerro Tololo Inter-American Observatory, and the National Optical Astronomy Observatory, which are operated by AURA under cooperative agreement with the American National Science Foundation; the National Radio Astronomy Observatory, which is a facility of the American National Science Foundation operated under cooperative agreement by Associated Universities, Inc.; and the Canada-France-Hawaii Telescope operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France and the University of Hawaii. The photometric redshifts used here were validated using spectra from the European Southern Observatory Very Large Telescope zCOSMOS survey. We gratefully acknowledge the contributions of the entire COSMOS collaboration, consisting of more than 70 scientists. We thank T. Roman, D. Taylor and D. Soderblom for help scheduling the extensive COSMOS observations; and A. Laity, A. Alexov, B. Berriman and J. Good for managing online archives and servers for the COSMOS data sets at NASA IPAC/IRSA. This work was supported by grants from NASA (to N.S. and R.M.).

Author Contributions A.K. processed the raw HST data, and J.-P.K. masked defects in the image. A.L., J.R. and R.M. catalogued the positions and shapes of galaxies. Y.T. and S.S. obtained multicolour follow-up data, which was processed and calibrated by S.S., P.C., H.McC. and H.A. P.C. determined galaxies’ redshifts, and B.M. their stellar mass. N.S. constructed maps of stellar mass and galaxy density. A.F. processed the X-ray image and removed point sources. R.M. and A.R. produced the two-dimensional and tomographic mass maps; J.-L.S. and S.P. developed the wavelet filtering technique. D.B. and A.T. produced the three-dimensional mass reconstruction. J.T., A.F., R.E. and R.M. compared the various tracers of large-scale structure.

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Correspondence to Richard Massey.

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Supplementary Information

This file contains Supplementary Figures S1-S7 and Supplementary Table S1. Figure S1 illustrates the process of gravitational lensing. Figure S2 shows spurious signal due to imperfect Charge Transfer Efficiency (CTE) before correction. Figure S3 shows correction for Charge Transfer Efficiency (CTE). Figure S4 shows realisation of noise level in the tomographic mass reconstructions. Figure S5 shows photometric redshift accuracy for bright galaxies. Figure S6 shows measured and expected number counts of faint galaxies. Figure S7 shows additional views of the 3 dimensional mass reconstruction. Table S1 shows dilution of the lensing signal by the spurious inclusion of low redshift galaxies at high redshift. (PDF 3354 kb)

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Massey, R., Rhodes, J., Ellis, R. et al. Dark matter maps reveal cosmic scaffolding. Nature 445, 286–290 (2007).

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