Improving constraints on primordial non-Gaussianity from Quaia with a new cosmological observable: Angular redshift fluctuations

Angular redshift fluctuations (ARFs) are a new cosmological observable recently proposed in the literature. It measures the 2D angular deviations of the average redshift of a given matter tracer under an input redshift shell. Since it depends on galaxy bias, it can be used to constrain primordial non-Gaussianity through the scale-dependent bias effect. We analyzed a sample of quasars built on Gaia satellite and unWISE data, Quaia to measure the local non-Gaussianity parameter f_ NL. This sample is particularly suitable for measuring f_ NL due to its large volume coverage. We measured the ARF power spectra from the Quaia catalog and combined their information with the 2D (projected) galaxy density and their cross-correlation with the Planck PR4 cosmic microwave background lensing maps to jointly constrain f_ NL. Assuming the universality relation, we measure f_ ̊m NL = -3 ± 14 at the 68% confidence level by combining Quaia quasar angular density and ARFs with their CMB lensing cross-correlations. Neglecting the ARF - CMB lensing cross-correlation leads to a significant improvement in the model's goodness-of-fit and yields comparable constraints, f_ ̊m NL = -5^ +16 _ -15 . This result is the second tightest constraint on f_̊m NL using LSS two-point statistics to date and the best measurement achieved using two-point projected summary statistics, improving the previous measurement from Quaia by up to ∼25%. Our results support the inclusion of ARFs as an additional cosmological observable in future 2D analyses of upcoming datasets from large surveys.