Prof. David Alonso

Abstract:

Abstract We present a quadratic estimator that detects and reconstructs spatially-varying multiplicative (m −) bias in weak lensing shear measurements, by exploiting the EB mode coupling that it generates. The method combines E and B modes with inverse-variance weights, to yield an unbiased reconstruction of $m(\boldsymbol{\theta })$ to first order. We study the ability of future Stage IV surveys to obtain an unbiased reconstruction of the m-bias in differing scenarios, considering differing bias morphologies, and characteristic scales, as well as differing metrics to quantify the signal-to-noise ratio of the reconstructed map. We consider an m pattern repeating on ~1○ × 1○ sky patches, as might be the case for an m field caused by focal-plane systematics. With a Euclid-like redshift distribution, we find that ~5 % rms variations in m-bias may be detected at the 20σ level, after stacking between ~400 and ~1000 patches (rising to between ~2800 and ~7600 for 1 % rms variations, data volumes that are becoming available with upcoming surveys), depending on the morphology of the m pattern. We show that these results are robust against the cosmological model assumed in the reconstruction, as well as the presence of intrinsic alignments or baryonic effects, and that the method shows no spurious response to additive (c −) bias. These results demonstrate that percent-level, spatially-varying m −bias can be detected at high significance, enabling diagnosis and mitigation in the Stage IV weak lensing era.

Abstract:

<jats:title>Abstract</jats:title> <jats:p> We analyse the large-scale angular clustering of quasars in the <jats:italic>Gaia</jats:italic> - <jats:italic>unWISE</jats:italic> quasar catalog, <jats:italic>Quaia</jats:italic> , and their cross-correlation with maps of the lensing convergence of the Cosmic Microwave Background (CMB), to constrain the level of primordial non-Gaussianity (PNG). Specifically, we target the scale-dependent bias that would be induced by PNG on biased tracers of the matter inhomogeneities on large scales. The <jats:italic>Quaia</jats:italic> sample is particularly well suited for this analysis, given the large effective volume covered, and our ability to map out the main potential sources of systematic contamination and mitigate their impact. Using the universality relation to characterise the response of the quasar overdensity to PNG ( <jats:italic> p <jats:sub>ϕ</jats:sub> </jats:italic> = 1), we report constraints on the local-type PNG parameter   <jats:italic>f</jats:italic> <jats:sub>NL</jats:sub> of <jats:italic>f</jats:italic> <jats:sub>NL</jats:sub> = -20.5 <jats:sup>+19.0</jats:sup> <jats:sub>-18.1</jats:sub> (68% C.L.) by combining the quasar auto-correlation and its cross-correlation with CMB lensing in two tomographic redshift bins (or <jats:italic>f</jats:italic> <jats:sub>NL</jats:sub> = -28.7 <jats:sup>+26.1</jats:sup> <jats:sub>-24.6</jats:sub> if assuming a lower response for quasars, <jats:italic> p <jats:sub>ϕ</jats:sub> </jats:italic> = 1.6). The error on <jats:italic>f</jats:italic> <jats:sub>NL</jats:sub> can be further improved if the cross-correlation between the tomographic redshift bins is included. Using the CMB lensing cross-correlations alone, we find <jats:italic> f <jats:sub>NL</jats:sub> </jats:italic> = -13.8 <jats:sup>+26.7</jats:sup> <jats:sub>-25.0</jats:sub> and <jats:italic> f <jats:sub>NL</jats:sub> </jats:italic> = -15.6 <jats:sup>+42.3</jats:sup> <jats:sub>-34.8</jats:sub> for <jats:italic> p <jats:sub>ϕ</jats:sub> </jats:italic> = 1 and <jats:italic> p <jats:sub>ϕ</jats:sub> </jats:italic> = 1.6 respectively. These are the tightest constraints on <jats:italic> f <jats:sub>NL</jats:sub> </jats:italic> to date from angular clustering statistics and cross-correlations with CMB lensing. </jats:p>