Tide-and-Seek: Anisotropic scale-dependent bias in the Lyman-alpha forest and designer samples

Abstract

Searches for primordial non-Gaussianity are powerful ways of learning new information about the early Universe. Observing primordial signals in the late Universe is challenging as, in general, it is difficult to disentangle the small, primordial signatures from the complex physics that describes the distribution of galaxies and large-scale cosmic structures. We demonstrate that scale-dependent bias from primordial non-Gaussianity with non-trivial directional dependence in the squeezed limit (also known as anisotropic primordial non-Gaussianity) can arise in a much larger class of tracers than previously considered. This is a smoking gun signature of primordial Universe physics that cannot be mimicked by late-Universe processes. We demonstrate this explicitly with simulations of the Lyman-$α$ forest and halos selected through their projected shape. The former is a standard cosmological probe and standard analyses could be simply extended to constrain this. The latter provides an interesting new approach: design samples with strong selection effects to provide new sensitivity to primordial physics. As a demonstration of these concepts, we apply this method to BOSS DR12 data, finding no evidence of anisotropic non-Gaussianity.