István Szapudi’s research while affiliated with University of Hawaiʻi at Mānoa and other places

The Cosmic Dawn Survey Pre-launch (PL) catalogues cover an effective 10.13 deg$^{2}$ area with uniform deep Spitzer/IRAC data ($m\sim25$ mag, 5$\sigma$), the largest area covered to these depths in the infrared. These data are used to gain new insight into the growth of stellar mass across cosmic history by characterising the evolution of the galaxy stellar mass function (GSMF) through $0.2 < z \leq 6.5$. The total volume (0.62 Gpc$^{3}$) represents a tenfold increase compared to previous works that have explored $z > 3$ and significantly reduces cosmic variance, yielding strong constraints on the abundance of massive galaxies. Results are generally consistent with the literature but now provide firm estimates of number density where only upper limits were previously available. Contrasting the GSMF with the dark matter halo mass function suggests that massive galaxies ($M \gtrsim10^{11}$ M$_{\odot}$) at $z > 3.5$ required integrated star-formation efficiencies of $M/(M_{\rm h}f_{\rm b}) \gtrsim$ 0.25--0.5, in excess of the commonly-held view of ``universal peak efficiency" from studies on the stellar-to-halo mass relation (SHMR). Such increased efficiencies imply an evolving peak in the SHMR at $z > 3.5$ which can be maintained if feedback mechanisms from active galactic nuclei and stellar processes are ineffective at early times. In addition, a significant fraction of the most massive quiescent galaxies are observed to be in place already by $z\sim 2.5$--3. The apparent lack in change of their number density by $z\sim 0.2$ is consistent with relatively little mass growth from mergers. Utilising the unique volume, evidence for an environmental dependence of the galaxy stellar mass function is found all the way through $z\sim 3.5$ for the first time, though a more careful characterisation of the density field is ultimately required for confirmation.

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. [Abridged]

We constrain AvERA cosmologies in comparison with the flat $\Lambda$CDM model using cosmic chronometer (CC) data and the Pantheon+ sample of type Ia supernovae (SNe Ia). The analysis includes CC fits performed with the \texttt{emcee} sampler and supernova fits based on a custom Markov Chain Monte Carlo implementation. For model comparison, we apply Anderson-Darling tests on normalized residuals to assess consistency with a standard normal distribution. Best-fit parameters are derived within the redshift ranges $z \leq 2$ for CCs and $z \leq 2.3$ for SNe. The best-fit values of the Hubble constant are ${H_0=68.28_{-3.24}^{+3.23}~\mathrm{km~s^{-1}~Mpc^{-1}}}$ from the CC analysis and ${H_0=71.99_{-1.03}^{+1.05}~\mathrm{km~s^{-1}~Mpc^{-1}}}$ from the SN analysis, for the AvERA cosmology. These results are consistent within $1\sigma$ with the corresponding AvERA simulation value of H(z=0). Both the CC and SN datasets substantially favor AvERA cosmologies over the flat $\Lambda$CDM model. We have identified signs of overfitting in both models, which suggests the possibility of overestimating the uncertainties in the Pantheon+ covariance matrix.

We discuss what we call halo or galaxy root systems, collections of particle pathlines that show the infall of matter from the initial uniform distribution into a collapsed structure. The matter clumps as it falls in, producing filamentary density enhancements analogous to tree roots and branches, blood vessels, or even human transportation infrastructure in cities and regions. This relates to the larger-scale cosmic web, but is defined locally about one of its nodes; a physical, geometric version of a merger tree. We find dark-matter-halo root systems on average to exhibit more roots and root branches for the largest cluster haloes than in small haloes. This may relate to the `cosmic-web detachment' mechanism that likely contributes to star-formation quenching in galaxy groups and clusters. We also find that high spin manifests in these root systems as curvier roots.

The Cosmic Dawn Survey (DAWN survey) provides multiwavelength (UV/optical to mid-IR) data across the combined 59 deg ² of the Euclid Deep and Auxiliary fields (EDFs and EAFs). In this work, the first public data release from the DAWN survey is presented. The catalogues made available herein consist of a subset of the full DAWN survey that includes two EDFs: EDF North (EDF-N) and EDF Fornax (EDF-F). Each field has been covered by the ongoing Hawaii Twenty Square Degree Survey (H20), which includes imaging from the CFHT MegaCam in the u filter and from the Subaru Hyper Suprime-Cam (HSC) in the griz filters. Each field has been further covered by Spitzer /IRAC 3.6–4.5µm imaging spanning 10 deg ² and reaching ~25 mag AB (5 σ ). All present H20 imaging and all publicly available imaging from the aforementioned facilities were combined with the deep Spitzer /IRAC data to create source catalogues spanning a total area of 16.87 deg ² in EDF-N and 2.85 deg ² in EDF-F for this first release. These catalogues are referred to as the ‘pre-launch’ (PL), as Euclid data is not yet public for these fields and therefore it is not included. Photometry was measured from these multiwavelength data using The Farmer , a novel and well validated model-based photometry code. Photometric redshifts and stellar masses were computed using two independent codes for modelling spectral energy distributions: EAZY and LePhare . Photometric redshifts show good agreement with spectroscopic redshifts ( σ NMAD ~ 0.5, η < 8% at i < 25). Number counts, photometric redshifts and stellar masses were further validated in comparison to the COSMOS2020 catalogue. The DAWN survey PL catalogues are designed to be of immediate use in these two EDFs and will be continuously updated and made available as both new ground-based data and spaced-based data from Euclid are acquired and made public. Future data releases will provide catalogues of all EDFs and EAFs and include Euclid data.

The discrepancy between low and high redshift Hubble constant H0 measurements is the highest significance tension within the concordance ΛCDM paradigm. If not due to unknown systematics, the Hubble puzzle suggests a lack of understanding of the universe’s expansion history despite the otherwise spectacular success of the theory. We show that a Gödel inspired slowly rotating dark-fluid variant of the concordance model resolves this tension with an angular velocity today ω0 ≃ 2 × 10−3 Gyr-1. Curiously, this is close to the maximal rotation, avoiding closed time-like loops with a tangential velocity less than the speed of light at the horizon.

The discrepancy between low and high redshift Hubble constant $H_0$ measurements is the highest significance tension within the concordance $\Lambda$CDM paradigm. If not due to unknown systematics, the Hubble puzzle suggests a lack of understanding of the universe's expansion history despite the otherwise spectacular success of the theory. We show that a G\"odel inspired slowly rotating dark-fluid variant of the concordance model resolves this tension with an angular velocity today $\omega_0 \simeq 2\times 10^{-3}$~Gyr\textsuperscript{-1}. Curiously, this is close to the maximal rotation, avoiding closed time-like loops with a tangential velocity less than the speed of light at the horizon.

We present the results of a novel type of numerical simulation that realizes a rotating Universe with a shear-free, rigid body rotation inspired by a Gödel-like metric. We run cosmological simulations of unperturbed glasses with various degrees of rotation in the Einstein–de Sitter and the $\Lambda$ Λ CDM cosmologies. To achieve this, we use the N-body code capable of simulating the infinite Universe, overcoming the technical obstacles of classical toroidal (periodic) topologies that would otherwise prevent us from running such simulations. Results show a clear anisotropy between the polar and equatorial expansion rates with more than $1~\%$ 1 % deviation from the isotropic case for maximal rotation without closed timeline curves within the horizon, $\omega _{0} \approx 10^{-3}$ ω 0 ≈ 10 - 3 $\hbox {Gyr}^{-1}$ Gyr - 1 ; a considerable effect in the era of precision cosmology.

The integrated Sachs–Wolfe (ISW) effect from stacking cosmic microwave background (CMB) images of superclusters and voids persists as a challenge to the concordance ΛCDM paradigm. The signal is 4–5 times the expectation. The CMB Cold Spot (CS), the most significant CMB anomaly, resulted in the discovery of the Eridanus supervoid, one of the most enormous known structures. Bayesian statistics and a later Dark Energy Survey (DES) analysis suggest it is responsible for the CS, consistent with the observed fourfold enhancement over concordance predictions. These results motivate the average expansion rate approximation (AvERA) model, tracking coarse-grained inhomogeneities in an N-body simulation. The AvERA expansion history provides a ‘late solution’ to the Hubble-constant tension with emerging curvature taking the role of Dark Energy, is consistent with all principal CMB and large-scale structure measurements, and solves the ISW puzzle. In addition, it predicts a sign reversal of the ISW effect that has been recently confirmed, albeit at a moderate significance, with eBOSS quasars. Deep and wide galaxy surveys, such as Euclid, will soon confirm or refute the ‘late complexity’ indicated by the ISW sign reversal, increase the overall statistical significance of the findings and settle whether the ISW puzzle necessitates any significant modification to the concordance ΛCDM paradigm. This article is part of the discussion meeting issue ‘Challenging the standard cosmological model’.