New Techniques to Measure Velocities in Our Universe

The evolution of structures in the Universe is thought to be a hierarchical process driven by gravitational instability acting on primordial density fluctuations. The Universe expand according to Hubble's law while galaxies and clusters fall towards each other because of gravity with an additional velocity component called the peculiar velocity.  Peculiar velocities are sensitive to different cosmological models based on dark energy or modified gravity scenarios.

Clusters of galaxies show their imprint in CMB maps on arc-minute scales due to the Sunyaev-Zeldovich (SZ) effect.  I will discuss how SZ effect can be used to measure the peculiar velocities of clusters of galaxies.  I will then discuss how peculiar velocities can be used to measure various cosmological parameters and used as a probe for modified gravity theories.

Peculiar velocities can also be measured by observing Type Ia Supernovae (SNeIa).  SNeIa are standard candles and their distance measures along with their redshifts can be used to derive the velocities of galaxies hosting SNeIa. I will discuss how a sample of large number of SNeIa, that will be discovered by surveys like LSST, can be used to measure the mean relative velocities of SNeIa.  This measurement requires no additional observational effort and provides complementary information about cosmology compared to that obtainable from the SNeIa luminosity distance measures.