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 multitracer approach. Furthermore we then include cosmic microwave background (CMB) lensing from a CMB Stage 4 experiment in the multitracer, which can improve the constraints on bias parameters. We forecast sigma(f(NL)) similar or equal to 0.9 (1.4) by combining SKA1, a Euclid-like (LSST-like) survey, and CMB Stage 4 lensing. With CMB lensing, the precision on f(NL) improves by up to a factor of 2, showing that a joint analysis is important. In the case with running of f(NL), our results show that the combination of upcoming cosmological surveys could achieve sigma(n(NL)) similar or equal to 0.12 (0.22) on the running index.
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