Constraints on local primordial non-Gaussianity from large scale structure

TL;DR

This paper investigates how local primordial non-Gaussianity affects large scale structure bias, deriving theoretical predictions, testing assumptions, and setting observational limits on the non-Gaussianity parameter f_NL.

Contribution

It rederives the scale-dependent bias effect within peak-background split, explores how halo merging history influences this bias, and provides observational constraints on f_NL using large scale structure data.

Findings

Limit on f_NL: -29 to +70 at 95% confidence assuming simple models.

Limits weaken to -31 to +70 if recent mergers are considered.

Results are comparable to WMAP 5-year constraints, with no positive detection.

Abstract

Recent work has shown that the local non-Gaussianity parameter f_NL induces a scale-dependent bias, whose amplitude is growing with scale. Here we first rederive this result within the context of peak-background split formalism and show that it only depends on the assumption of universality of mass function, assuming halo bias only depends on mass. We then use extended Press-Schechter formalism to argue that this assumption may be violated and the scale dependent bias will depend on other properties, such as merging history of halos. In particular, in the limit of recent mergers we find the effect is suppressed. Next we use these predictions in conjunction with a compendium of large scale data to put a limit on the value of f_NL. When combining all data assuming that halo occupation depends only on halo mass, we get a limit of -29 ~ (-65)< f_NL < +70 ~(+93) at 95% (99.7%) confidence. While we use a wide range of datasets, our combined result is dominated by the signal from the SDSS photometric quasar sample. If the latter are modeled as recent mergers then the limits weaken to -31 ~(-96) < f_NL < +70 ~ (+96) . These limits are comparable to the strongest current limits from the WMAP 5 year analysis, with no evidence of a positive signal in f_NL. While the method needs to be thoroughly tested against large scale structure simulations with realistic quasar and galaxy formation models, our results indicate that this is a competitive method relative to CMB and should be further pursued both observationally and theoretically.