NBIA Seminar: Mohamed Rameez


Finding a lump in the Universe

The dipolar anisotropy of the CMB is believed to be due to our motion with respect to the CMB rest frame at 369 km/s. This should cause a dipolar modulation in the number counts of distant sources, through special relativistic aberration and Doppler boosting effects. We test this with various all-sky catalogues: NVSS and SUMSS radio galaxies, WISE galaxies and Quasars as well as GAIA-unWISE AGNs and consistently find a significantly larger dipole than expected, implying velocities >1000 km/s at conservative statistical significances as high as 3.3 sigma. These and other observations hint at a bulk displacement between the matter and radiation rest frames in the local Universe, extending out to scales larger than is typical in Lambda CDM N-body simulations. An observational effect of such a bulk flow would be a scale dependent dipolar modulation in the deceleration parameter. We look for this in the SDSS-II/SNLS-III Joint lightcurve analysis catalogue of SN1a curves and find such a modulation at >3.4 sigma statistical significance, while the evidence for any isotropic acceleration of the Universe simultaneously drops to <1.4 sigma. These observations and other curious features of SN1a data, as well as a significant body of literature from the classical general relativistic picture of cosmology suggest that Lambda CDM may merely be an approximate model of the "lumpy" Universe of Ellis and Stoeger 1987.