Verein für datenintensive Radioastronomie e.V.

Verein für datenintensive Radioastronomie e.V.

AUF DEM WEG ZUR PRÄZISIONSKOSMOLOGIE

Expansion des Universums

Quelle: NASA / WMAP Science Team simple retouch by Yikrazuul

Recent progress in defining the standard cosmological model – known as ΛCDM – has been dominated by observa- tions of the Cosmic Microwave Background (CMB, Hinshaw et al. 2013; Planck Collaboration et al. 2016a, 2018). Maps of the microwave sky made by the Planck satellite between 30 and 857 GHz, have allowed almost cosmic variance limited measurements of the temperature anisotropy spectrum out to multipoles in excess of l = 1000 as well as high fidelity measurements of the polarization of the CMB. These measurements have constrained  five of the standard six parameters ΛCDM to 1% precision and the final one (the optical depth to reionization) to 10%. The parameter constraints from CMB observations are broadly compatible with other cosmological indicators such as measurements of the cosmic distance scale using standard candles (Cepheids and Supernovae, Astier et al. 2006) and number counts of clusters of galaxies (Planck Collaboration et al., 2016c).

A wide range of physical phenomena can be probed beyond the ΛCDM model. These include the dark sector which is responsible for cosmic acceleration, massive neutrinos and primordial non-Gaussianity. Although these phenomena can be constrained with further observations of the CMB, probes of large scale structure, mapping the Uni- verse at relatively lower redshifts, are essential to break some of the degeneracies inherent in CMB observations.

Measurements of the matter power spectrum through galaxy redshift surveys have been around for some time (Cole et al., 2005), indeed before the detection of the CMB anisotropies, and have played a significant role in defining ΛCDM (Efstathiou et al., 1990). The next two decades will see rapid progress in the field of Large Scale Structure (LSS) surveys with the advent of the Euclid Satellite (Laureijs et al., 2011a), the Large Synoptic Survey Telescope (LSST, LSST Science Collaboration et al. 2009) and the Dark Energy Spectroscopic Instrument (DESI, DESI Collaboration et al. 2016) which will create large scale maps of the Universe. In particular they will use measurements of the angular positions and redshifts of galaxies to infer the matter power spectrum, facilitating measurements of Baryonic Acoustic Oscillations (BAOs) and Redshift Space Distortions (RSDs), and measurements of cosmic shear power spectrum by estimation of galaxy shapes. There are many challenges in achieving the fantastic levels of statistical precision which will be possible with these instruments, notably reducing the levels of observational systematic errors.

The SKA will be an important further step towards  high precicsion cosmology. Three cosmological surveys are envisioned with the SKA: a medium-deep continuum weak lensing and low-redshift spectroscopic HI galaxy survey over 5,000 deg2; a wide and deep continuum galaxy and HI intensity mapping survey over 20,000 deg2 from z = 0.35 − 3; and a deep, high-redshift HI intensity mapping survey over 100 deg2 from z = 3 − 6. Taken together, these surveys will achieve an array of important scientific goals: measuring the equation of state of dark energy out to z ∼ 3 with percent-level precision measurements of the cosmic expansion rate; constraining possible deviations from General Relativity on cosmological scales by measuring the growth rate of structure through multiple independent methods; mapping the structure of the Universe on the largest accessible scales, thus constraining fundamental properties such as isotropy, homogeneity, and non-Gaussianity; and measuring the HI density and bias out to z = 6. These surveys will also provide highly complementary clustering and weak lensing measurements that have independent systematic uncertainties to those of optical surveys like LSST and Euclid, leading to a multitude of synergies that can improve constraints significantly beyond what optical or radio surveys can achieve on their own.

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Thema von Anders Norén