Session M03: Early Universe and Reionization

Status of 21cm Intensity Mapping with CHIME

Intensity mapping of redshifted 21cm emission from neutral hydrogen holds great promise for learning about cosmology, as it provides an efficient way to map large volumes of the universe without the need to characterize individual luminous sources. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a cylinder telescope located in Western Canada that was custom-built for this purpose, and that has collected several years worth of data since it reached full observational capacity in late 2018. I will present a status update on recently-completed and ongoing cosmological analyses of CHIME data, including cross-correlations with galaxy/quasar catalogs from the extended Baryon Oscillation Spectroscopic Survey (eBOSS), cross-correlations with Lyman-alpha forest measurements from eBOSS, and progress toward a measurement of the auto power spectrum of the cosmological 21cm signal between redshifts 0.8 and 2.5.   

Reconstructing the recombination history using cosmic microwave background and baryon acoustic oscillation data

We present a data-driven reconstruction of the ionization history during the epoch of recombination, leveraging the constraining power of both cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) data sets. This constraining power arises mostly from the sensitivity of acoustic peak locations to the redshift of recombination, and the sensitivity of both the diffusion damping scale and small-scale polarization amplitude to the duration of recombination. Our approach avoids a commonly used linear response approximation, because it would lead to significantly biased results. The reconstructed ionization history is consistent with the standard recombination history, although parameter constraints are impacted due to the newly introduced degeneracies. We find that modifications to recombination can alleviate the Hubble tension to varying degrees depending on the datasets used. The 95% confidence upper limits on H0 are 73.0 (70.2) km/s/Mpc when CMB (CMB+BAO) data are included, assuming no other changes are made to the standard cosmological model. We forecast that adding forthcoming SPT-3G measurements to Planck and existing BAO data will shrink the constraints on the ionization history by about a factor of two.   

Probing non-Gaussianity beyond the local-type with kSZ tomography

Primordial non-Gaussianity remains a key target for studying the physics of the early Universe. In this talk, I will discuss how kinematic Sunyaev-Zeldovich (kSZ) tomography has promise as a powerful probe of primordial non-Gaussianity beyond the standard local type. In particular, primordial non-Gaussianity can manifest as a source of scale-dependent galaxy bias. By using kSZ tomography as an additional probe of the large scale matter power spectrum, a better measurement of the scale-dependent galaxy bias is possible, enabling improved inference of the parameters that control the amplitude and shape (squeezed, equilateral, etc.) of the bispectrum of primordial curvature perturbations. I will also discuss discuss the robustness of these results to various biases, degeneracies, and survey details.   

Advancing Normalizing Flows for Correlated Non-Gaussian Fluctuations in Cosmological Simulations

We present a technique to improve the accuracy and training efficiency of normalizing flows for multiple images in the context of cosmology. Normalizing flows are powerful deep generative models that can learn complex probability distributions through invertible transformations applied to a simple distribution. They are well-suited for both image generation and density estimation, enabling precise likelihood evaluation and efficient sampling. However, due to the inherent constraint of invertibility, normalizing flows exhibit limited expressiveness when compared to other well-known models like GANs. Yet, past research has demonstrated that this limitation can be addressed by employing more expressive priors, such as resampled normal Gaussian or correlated priors, effectively enhancing the capabilities of normalizing flows. Our ongoing work focuses on developing a technique to enable normalizing flows to capture correlated non-Gaussian fluctuations in realistic mm-wave extragalactic foreground simulations, which consist of multiple components, based on N-body simulations. As part of this endeavor, we investigate and compare the efficiency of normalizing flows in generating two-component correlated non-Gaussian maps using various priors. The three priors considered are as follows: the normal distribution (the simplest setup), the correlated prior (which incorporates the auto-spectrum of each target maps but not their correlations), and the component-correlated prior (which incorporates both the auto- and the cross-spectra of the target maps). We find that, when dealing with $f_{nl}$ type local non-Gaussianity the application of correlated and component-correlated priors results in more accurate representations of the target distribution compared to other approaches. We will next apply this on realistic simulations of the CMB lensing convergence and extragalactic foreground fields, with the goal of field-level inference with mm-wave data.