![]() ![]() ![]() As an example, measurements of weak gravitational lensing and galaxy clustering using the first year of data from the Dark Energy Survey resulted in a constraint of Ω m = 0.27 − 0.02 + 0.03 ( Abbott et al., 2018). Gravitational lensing is detected through the statistics of galaxy shapes. Velocities are probed through the characteristic distortion they imprint on the three-dimensional statistics of galaxy number counts. 13, large-scale structure provides two beautiful ways to probe gravitational potential wells and hence the amount of matter: galaxy velocities and gravitational lensing. When combined with the CMB, the constraint becomes very tight, yielding Ω m = 0.311 ± 0.006.Īs we will see in Ch. The distance-redshift relation in the late universe, as probed by standard candles and rulers, constrains Ω m alone. Therefore, again invoking our knowledge of the Hubble constant, the CMB observations are consistent with a matter density equal to about 30% of the critical density. Assuming the concordance model, the Planck team reported Ω m h 2 = 0.1431 ± 0.0025 ( Planck Collaboration, 2018b). The sensitivity of the CMB to the matter density is both due to the effect of matter on the expansion history in the early universe, as well as the fact that dark matter dominates the gravitational potential wells which also leave their imprint in the CMB anisotropies. 9) provide a measurement of the physical matter density parameter Ω m h 2. But how do we measure the total density of matter? Unlike for baryons, we cannot use nuclear and atomic physics, but have to rely on gravity. 1, the overwhelming evidence for (non-baryonic) dark matter is not a new revelation to astronomers, who have found corresponding evidence within our Milky Way and local group, as well as other galaxies and clusters of galaxies. Scott Dodelson, Fabian Schmidt, in Modern Cosmology (Second Edition), 2021 2.4.3 Dark matterĪs we mentioned in Ch. ![]()
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