Removing interlopers from intensity mapping probes of primordial non-Gaussianity

Abstract

ABSTRACT Line intensity mapping (LIM) has the potential to produce highly precise measurements of scale-dependence bias from primordial non-Gaussianity (PNG) due to its ability to map much larger volumes than are available from galaxy surveys. However, LIM experiences contamination from foreground emission, including interloping emission lines from other redshifts that alter the power spectra of the maps at these scales, potentially biasing measurements of fNL. Here, we model the effect of line interlopers on upcoming LIM probes of PNG from inflation. As an example, we consider the $[\rm C\,{{\small II}}]$ line at target redshift zt = 3.6 to probe PNG, with the important systematic concern being foreground contamination from CO lines residing at redshifts different from the target redshift. We find interloper lines can lead to a significant bias if we neglect the interlopers in the parameter estimation. Including the interlopers in the parameter estimation would cause an increase in errors for our PNG constraints, leading to a false positive for non-standard inflation models. We model how well the cross-correlation technique could reduce this interloper contamination using $[\rm C\,{\small II}]$ and CO(4–3) at the same redshift and find the uncertainty of fNL reduces by factors of 2 and 6 for local and orthogonal shape PNG, respectively, and by a factor of 5 for local shape if we consider seven interloper lines. This shows that when jointly fitting the auto- and cross-spectrum in the presence of interlopers, the errors are comparable to those from fitting without interlopers, almost eliminating the effect of interlopers when measuring non-Gaussianity.