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Signatures of peculiar velocities in the cosmic microwave background: University of Southern California

Elena Pierpaoli

[email protected]

The statistics of the peculiar velocity field of galaxy clusters (i.e., motions not related to expansion of the universe) are highly informative about the nature of dark matter, dark energy, and the theory of gravity. Currently, peculiar velocity measurements on large scales are limited to only the line-of-sight components of clusters, leaving most of the available information in the velocity field inaccessible to us. The yet-undetected transverse components can be traced through the cosmic microwave background (CMB) via two effects: (i) the Birkinshaw-Gull (BG) effect in CMB temperature, and (ii) the Kinetic Sunyaev-Zeldocivh (kSZ) effect in CMB polarization. In this research, we make a realistic assessment of the detectability of these signals with the near future CMB experiments, and also investigate the possibility of exploiting the statistics of these signals for cosmology. The PI will develop a creative educational product for K-12 students to promote awareness of and interest in physics and cosmology, in particular the physics of galaxy clusters and structure formation. K-12 teachers will be trained to use this educational product leveraging on existing relationships via the USC family of schools. The developed material will also be available online for all educators willing to download and use it.<br/> <br/>The amplitude of both BG and kSZ effects are subdominant with respect to the primary CMB anisotropies and current instrumental noise levels. Aside from this, the signals can be confused with other emissions from within and outside the clusters, gravitational lensing effects, and uncertainties in clusters' physical description. Therefore, it is almost impossible to observe these effects for individual objects. Nevertheless, it is still possible to achieve a successful detection of them by employing novel statistical methods in the analysis of data. One example is to use pairwise statistical estimators which have been shown to significantly increase the detection signal-to-noise ratio. Throughout this project we will investigate the possibility of measuring these signals in the near future using the next generation of CMB surveys. We will provide forecast analyses through semi-analytical and numerical simulations of clusters and introduce proper map-filtering techniques and new statistical tools for this purpose. The current general interest in producing larger and deeper CMB surveys with improved intensity and polarization sensitivities makes this an appropriate time to further the study of peculiar velocities and inspect their cosmological implications.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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