Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

Context. Baryonic physics has a considerable impact on the distribution of matter in our Universe on scales probed by current and future cosmological surveys, acting as a key systematic in such analyses. Aims. We seek simple symbolic parametrisations for the impact of baryonic physics on the matter power spectrum for a range of physically motivated models, as a function of wavenumber, redshift, cosmology, and parameters controlling the baryonic feedback. Methods. We used symbolic regression to construct analytic approximations for the ratio of the matter power spectrum in the presence of baryons to that without such effects. We obtained separate functions of each of four distinct sub-grid prescriptions of baryonic physics from the CAMELS suite of hydrodynamical simulations (Astrid, IllustrisTNG, SIMBA, and Swift-EAGLE) as well as for a baryonification algorithm. We also provide functions that describe the uncertainty on these predictions, due to both the stochastic nature of baryonic physics and the errors on our fits. Results. The error on our approximations to the hydrodynamical simulations is comparable to the sample variance estimated through varying initial conditions, and our baryonification expression has a root mean squared error of better than one percent, although this increases on small scales. These errors are comparable to those of previous numerical emulators for these models. Our expressions are enforced to have the physically correct behaviour on large scales and at high redshift. Due to their analytic form, we are able to directly interpret the impact of varying cosmology and feedback parameters, and we can identify parameters that have little to no effect. Conlcusions. Each function is based on a different implementation of baryonic physics, and can therefore be used to discriminate between these models when applied to real data. We provide a publicly available code for all symbolic approximations found.

Abstract:

ABSTRACT Several observational studies suggest that the local few hundred Mpc around the Local Group is significantly underdense based on source number counts in redshift space across much of the electromagnetic spectrum, particularly in near-infrared galaxy counts. This ‘Keenan–Barger–Cowie (KBC) void’, ‘Local Hole’, or ‘local supervoid’ would have significant ramifications for the Hubble tension by generating outflows that masquerade as an enhanced local expansion rate. We evaluate models for the KBC void capable of resolving the Hubble tension with a background Planck cosmology. We fit these models to direct distances from the Tully–Fisher catalogue of the CosmicFlows-4 compilation using a field-level forward model. Depending on the adopted void density profile, we find the derived velocity fields prefer a void size $\lesssim 70$ Mpc, which is $\lesssim 10$ per cent of the fiducial size found by Haslbauer et al. based on the KBC luminosity density data. The predicted local Hubble constant is $72.1^{+0.9}_{-0.8}$, $70.4^{+0.4}_{-0.4}$, or $70.2^{+0.5}_{-0.4}$ km s−1 Mpc−1 for an initial underdensity profile that is exponential, Gaussian, or Maxwell–Boltzmann, respectively. The latter two ameliorate the Hubble tension to within $3\sigma$ of the four-anchor distance ladder approach of Breuval et al., which gives $73.2 \pm 0.9$ km s−1 Mpc−1. The exponential profile achieves consistency with this measurement at just over $1\sigma$, but it is disfavoured by the Bayesian evidence. The preferred models produce bulk flow curves that disagree with recent estimates from CosmicFlows-4, despite the void models being flexible enough to match such estimates.

Abstract:

Abstract:

Observations over the past decade have shown that galaxy clusters undergo the most transformative changes during the z = 1.5–2 epoch. However, challenges such as low lensing efficiency, high shape measurement uncertainty, and a scarcity of background galaxies have prevented us from characterizing their masses with weak gravitational lensing (WL) beyond redshift z ∼ 1.75. In this paper, we report the successful WL detection of JKCS 041 and XLSSC 122 at z = 1.80 and z = 1.98, respectively, utilizing deep infrared imaging data from the Hubble Space Telescope with careful removal of instrumental effects. These are the most distant clusters ever measured through WL. The mass peaks of JKCS 041 and XLSSC 122, which coincide with the X-ray peak positions of the respective clusters, are detected at the ∼3.7σ and ∼3.2σ levels, respectively. Assuming a single spherical Navarro–Frenk–White profile, we estimate that JKCS 041 has a virial mass of M200c = (5.4 ± 1.6) × 1014 M⊙, while the mass of XLSSC 122 is determined to be M200c = (3.3 ± 1.8) × 1014 M⊙. These WL masses are consistent with the estimates inferred from their X-ray observations. We conclude that although the probability of finding such massive clusters at their redshifts is certainly low, their masses can still be accommodated within the current ΛCDM paradigm.