Observational Cosmology Seminar

The precision of ongoing and upcoming cosmological surveys such as the Dark Energy Spectroscopic Instrument (DESI), Vera C. Rubin Observatory, SPHEREx, and many others promise to rule out LCDM and extensions of it. However, the improvement in precision also comes with understanding non-cosmological accuracy biases; untreated, these biases could mimic cosmological signals. In the current era, the assumption and modeling of the Milky Way extinction has become one such critical sources of biases. In this talk, I will discuss results from three papers, the cross-correlation of DESI photometric emission-line galaxies (ELG) and the Planck CMB lensing, forecast of the cross-correlation of LSST z > 1 lens sample and the Simons Observatory CMB lensing, and the forecast of LSST type Ia supernovae cosmology. In each case, we find evidence of the impact of the extinction — an up to 1.2 sigma shift on the sigma8 - OmegaM plane (ELG X Planck), an up to 1.5sigma shift in fNL (LSST X SO), and a factor of 3 loss in precision in the dark energy figure of merit (SNIa). Additionally, we find evidence of scale-dependent suppression of power in the cross-correlation of photometric ELGs and the cosmic infrared background. These results together strongly suggest the need to revisit the formalism of joint likelihood analysis, and the need to jointly model the impact of foregrounds on galaxy clustering and supernovae analyses.