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

TL;DR

ARF provides a novel 2D observable sensitive to local primordial non-Gaussianity through scale-dependent bias. By combining Quaia quasar density, ARF, and Planck $CMB$ lensing in a joint angular power spectrum analysis, the authors obtain $f_{\rm NL} = -3 \pm 14$ (68% CL), improving the Quaia two-point constraint by about 25% and achieving one of the tightest LSS two-point bounds to date. The result showcases ARF's potential to enhance 2D clustering analyses for upcoming surveys and motivates broader adoption, while highlighting ongoing challenges in non-linear ARF modeling and systematic deprojection. Future work will focus on refining ARF theory, reducing photometric redshift systematics, and extending 2D analyses to DESI, Euclid, and LSST.

Abstract

Angular redshift fluctuations (ARF) 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 the galaxy bias, it can be used to constrain primordial non-Gaussianity through the scale-dependent bias effect. We analyze a sample of quasars built upon the Gaia satellite and unWISE data, Quaia, to measure the local non-Gaussianity parameter $f_{\rm NL}$. This sample is particularly suitable for measuring $f_{\rm NL}$ due to its large volume coverage. We measure the ARF power spectra from the Quaia catalog and combine their information with the 2D (projected) galaxy density and their cross-correlation with the $Planck$ PR4 CMB lensing maps lensing to jointly constrain $f_{\rm NL}$. Assuming the universality relation, we measure $f_{\rm NL} = -3 \pm 14$ at 68% confidence level by combining Quaia quasar angular density and ARF with the CMB lensing. This result is the second tightest constraint on $f_{\rm NL}$ using LSS two-point statistics to date and the best measurement achieved using two-point projected summary statistics, improving by $\sim$25% the previous measurement from Quaia. Our results motivate the inclusion of ARF as an additional cosmological observable in future 2D analysis of upcoming datasets from large surveys.

Figures (8)

• Figure 1: Normalized redshift distribution of the Quaia QSO sample analyzed in this paper. The black dashed line corresponds to the full sample, while the blue and red lines correspond to the low and high redshift bins, respectively.
• Figure 2: Upper panels: normalized masks from the Quaia selection functions applied in our analysis after applying a 0.5 threshold for the low-z and high-z redshift bins. Middle panels: Quaia density maps for the low-z and high-z redshift bins. Lower panels: Quaia ARF maps for the low-z and high-z redshift bins. The density and ARF maps are represented with a 1 degree beam smoothing.
• Figure 3: Measured angular power spectra of the Quaia density and ARF autocorrelations for the low redshift (left panel) and high redshift (right panel) bins. The dots represent the binned angular power spectra with errorbars, the dashed lines the theoretical model with $f_{\rm NL} = 0$, and the dotted lines the same model after the parametrization of the measured excess of power.
• Figure 4: Measured angular power spectra of the Quaia density and ARF cross-correlations with the $Planck$ CMB lensing for the low redshift (left panel) and high redshift (right panel) bins. The dots represent the binned angular power spectra with errorbars and the dashed lines the theoretical fiducial model with $f_{\rm NL} = 0$.
• Figure 5: Comparison of the shift on the $\ell = 6$ and $\ell = 10$ angular power spectra of the Quaia high-z sample after applying systematics deprojection to the mocks and data for $C_\ell^{zz}$ (left panels) and $C_\ell^{\kappa z}$ (right panels), used to validate the scale cuts in our analysis. The blue bars represent the distribution of the shift on the 1000 mock realizations and the red lines the shift found in real data.