27 research outputs found

    Foreground-immune CMB lensing reconstruction with polarization

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    Extragalactic foregrounds are known to generate significant biases in temperature-based CMB lensing reconstruction. Several techniques, which include ``source hardening'' and ``shear-only estimators'' have been proposed to mitigate contamination and have been shown to be very effective at reducing foreground-induced biases. Here we extend both techniques to polarization, which will be an essential component of CMB lensing reconstruction for future experiments, and investigate the ``large-lens'' limit analytically to gain insight on the origin and scaling of foreground biases, as well as the sensitivity to their profiles.Using simulations of polarized point sources, we estimate the expected bias to both Simons Observatory and CMB-S4 like (polarization-based) lensing reconstruction, finding that biases to the former are minuscule while those to the latter are potentially non-negligible at small scales (L∼1000−2000L\sim1000-2000). In particular, we show that for a CMB-S4 like experiment, an optimal linear combination of point-source hardened estimators can reduce the (point-source induced) bias to the CMB lensing power spectrum by up to two orders of magnitude, at a ∼4%\sim4\% noise cost relative to the global minimum variance estimator.Comment: 18 pages, 7 figure

    Lower bias, lower noise CMB lensing with foreground-hardened estimators

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    Extragalactic foregrounds in temperature maps of the Cosmic Microwave Background (CMB) severely limit the ability of standard estimators to reconstruct the weak lensing potential. These foregrounds are not fully removable by multi-frequency cleaning or masking and can lead to large biases if not properly accounted for. For foregrounds made of a number of unclustered point sources, an estimator for the source amplitude can be derived and deprojected, removing any bias to the lensing reconstruction. We show with simulations that all of the extragalactic foregrounds in temperature can be approximated by a collection of sources with identical profiles, and that a simple bias hardening technique is effective at reducing any bias to lensing, at a minimal noise cost. We compare the performance and bias to other methods such as "shear-only" reconstruction, and discuss how to jointly deproject any arbitrary number of foregrounds, each with an arbitrary profile. In particular, for a Simons Observatory-like experiment foreground-hardened estimators allow us to extend the maximum multipole used in the reconstruction, increasing the overall statistical power by ∼50%\sim 50\% over the standard quadratic estimator, both in auto and cross-correlation. We conclude that source hardening outperforms the standard lensing quadratic estimator both in auto and cross-correlation, and in terms of lensing signal-to-noise and foreground bias.Comment: published in PR

    Optical depth to reionization from perturbative 21cm clustering

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    The optical depth τ\tau is the least well determined parameter in the standard model of cosmology, and one whose precise value is important for both understanding reionization and for inferring fundamental physics from cosmological measurements. We forecast how well future epoch of reionization experiments could constraint τ\tau using a symmetries-based bias expansion that highlights the special role played by anisotropies in the power spectrum on large scales. Given a parametric model for the ionization evolution inspired by the physical behavior of more detailed reionization simulations, we find that future 21cm experiments could place tight constraints on the timing and duration of reionization and hence constraints on τ\tau that are competitive with proposed, space-based CMB missions provided they can measure k≈0.1 h Mpc−1k\approx 0.1\,h\,\text{Mpc}^{-1} with a clean foreground wedge across redshifts spanning the most active periods of reionization, corresponding to ionization fractions 0.2≲x≲0.80.2 \lesssim x \lesssim 0.8. Significantly improving upon existing CMB-based measurements with next-generation 21cm surveys would require substantially longer observations (∼5\sim5 years) than standard O(1000  hour)\mathcal{O}(1000 \,\,\text{hour}) integration times. Precise measurements of smaller scales will not improve constraints on τ\tau until a better understanding of the astrophysics of reionization is achieved. In the presence of noise and foregrounds even future 21cm experiments will struggle to constrain τ\tau if the ionization evolution deviates significantly from simple parametric forms.Comment: published in JCA

    A Spectroscopic Road Map for Cosmic Frontier: DESI, DESI-II, Stage-5

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    In this white paper, we present an experimental road map for spectroscopic experiments beyond DESI. DESI will be a transformative cosmological survey in the 2020s, mapping 40 million galaxies and quasars and capturing a significant fraction of the available linear modes up to z=1.2. DESI-II will pilot observations of galaxies both at much higher densities and extending to higher redshifts. A Stage-5 experiment would build out those high-density and high-redshift observations, mapping hundreds of millions of stars and galaxies in three dimensions, to address the problems of inflation, dark energy, light relativistic species, and dark matter. These spectroscopic data will also complement the next generation of weak lensing, line intensity mapping and CMB experiments and allow them to reach their full potential.Comment: Contribution to Snowmass 202

    Optimal multifrequency weighting for CMB lensing

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    Cosmology at high redshift -- a probe of fundamental physics

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    An observational program focused on the high redshift ($
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