Constraining primordial non-Gaussianity using two galaxy surveys and CMB lensing

Next-generation galaxy surveys will be able to measure perturbations on scales beyond the equality scale. On these ultra-large scales, primordial non-Gaussianity leaves signatures that can shed light on the mechanism by which perturbations in the early Universe are generated. We perform a forecast analysis for constraining local type non-Gaussianity and its two-parameter extension with a simple scale-dependence. We combine different clustering measurements from future galaxy surveys – a 21cm intensity mapping survey and two photometric galaxy surveys – via the multi-tracer approach. Furthermore we then include CMB lensing from a CMB Stage 4 experiment in the multi-tracer, which can improve the constraints on bias parameters. We forecast σ(fNL) ≃ 0.9 (1.4) by combining SKA1, a Euclid-like (LSST-like) survey, and CMB-S4 lensing. With CMB lensing, the precision on fNL improves by up to a factor of 2, showing that a joint analysis is important. In the case with running of fNL, our results show that the combination of upcoming cosmological surveys could achieve σ(nNL) ≃ 0.12 (0.22) on the running index.