arXiv subjects

Geraint F. Lewis

Publications and source records attributed to Geraint F. Lewis.

At least 19 recordsLinked to original sources

arXiv2026

AGN Reverberation Mapping with LITMUS: Fundamental Limits on lag Recovery Rates

Reverberation mapping of active galactic nuclei provides one of the most direct probes of the geometry and kinematics of the broad-line region by measuring time delays between continuum and line variability. Modern RM surveys frequently suffer difficulties with lag measurements due to poor signal to noise and aliasing, whereby multimodal lag posterior distributions arise due to seasonal gaps in our data. These challenge the reliability of commonly used fitting tools such as JAVELIN, which can return a high rate of false positives. We implement a new lag measurement package, LITMUS, and introduce a new framework that uses Bayesian evidence to identify false positive lag measurements, as well as examine the question of how many AGN present detectable lags in high redshift industrial scale surveys like OzDES and SDSS. Our analysis differs from previous RM studies in six key respects: (i) our inference is robust to the previously under-diagnosed numerical component of aliasing, (ii) we use a consistent methodology for all sources, (iii) uncertainty in the underlying AGN variability is fully marginalised, (iv) lag significance is assessed via Bayesian model comparison rather than heuristic metrics, (v) false-positive rates are quantified by comparison against random-chance recoveries and (vi) we use marginal likelihoods to distinguish between sources where a lag is not detectable in our data and sources that show no evidence of reverberation. Applied to the OzDES sample, we find that previous RM studies are likely to have overestimated the confidence of recovered lags, and we find a stark contrast between a low reverberation percentage for the MgII line (3-28% depending on assumptions) and much higher percentages in the CIV and especially the H$β$ line, which is consistent with 100%. We also present a re-analysed set of lags from the OzDES sample with better quantified reliabilities

astro-ph.CO↗

arXiv2026

Cracking into RACS - I. Measuring the cosmic dipole in the RACS-low3 and RACS-mid1 radio surveys with simulation-based inference

We measure the dipole in the count of radio galaxies over the sky as seen by the Australian SKA Pathfinder (ASKAP) in the Rapid ASKAP Continuum Survey (RACS). Our analysis focuses on the third observational epoch in the 'low' passband (943.5 MHz; RACS-low3) and the first epoch in the 'mid' passband (1367.5 MHz; RACS-mid1). We find strong evidence for a systematic relation between flux density and the temperature at the time of observation, whereby reported flux densities are suppressed to a greater degree when the ASKAP antennas are warmer. We include this temperature response in our forward model as part of our Simulation-based Inference (SBI) pipeline, generating data realisations that are then used by a neural network to learn the likelihood function. Despite this model, RACS-low3 and RACS-mid1 both exhibit a dipole inconsistent with the kinematic dipole of the Cosmic Microwave Background (CMB), adding further evidence for the 'cosmic dipole tension'. For RACS-low3, the dipole agrees in direction but has an amplitude four times in excess, while the dipole for RACS-mid1 is offset from the CMB and has an amplitude roughly five times in excess. Our findings underscore the importance of interrogating the data for systematic effects and showcase the power of SBI in handling them.

astro-ph.CO↗

arXiv2026

Probing the Assembly of Triangulum: Precision Metallicities and $α$ Abundances of M33's Star Clusters from APOGEE Integrated-Light Spectroscopy

The star cluster system of M33 provides an excellent opportunity to investigate whether galaxy formation physics is dependent on a galaxy's mass. Older globular clusters (GCs) trace hierarchical assembly and chemical enrichment, while younger clusters trace the recent star formation. By studying the M33 star cluster system as a whole, we can probe the formation physics of galaxies at a lower mass than the Milky Way, and look for signals of accretion. To that end, we present analysis of 37 M33 star clusters using high-resolution ($R\sim22,500$), near-infrared (1.5-1.7 $μ$m), integrated light spectra from the APOGEE survey. We use full-spectrum fitting to obtain precision measurements of the clusters' kinematics, metallicities, and $α$ abundances. We identify three populations of clusters from our measurements: young stellar clusters (~100 Myr) with broad Brackett absorption features; intermediate-age clusters (1-2 Gyr) that are metal-rich ([M/H]=-0.5 to +0.3) with roughly solar $α$ abundance; and old (>5 Gyr), kinematically-hot and metal-poor GCs. These old GCs exhibit a broad range of kinematics (RV~-250 to -8 km s$^{-1}$), metallicities ([M/H]=-1.8 to -0.6) and $α$ abundances ([$α$/M]=+0.05 to +0.3), and we identify and discuss three GCs that show strong chemodynamical evidence of accretion into M33's halo. M33's GCs at [M/H]~-1.2 have a spread in [$α$/M] of nearly 0.2 dex. This pattern is strikingly similar to the abundance distribution of Milky Way GCs, and indicates either that M33 and the Milky Way formed clusters similarly at early times, or that M33 hosts a significant population of accreted clusters in its halo.

astro-ph.GA↗

arXiv2026

On the foundations of anthropic reasoning: Implications for life across the universe

With only one confirmed example, namely the Earth, the abundance of life across the universe remains deeply uncertain, and local evidence about Earth's particular circumstances can significantly shape our knowledge of life elsewhere. Such extrapolation is difficult not only because of this sample size of one, but also due to observer selection effects discussed under the Anthropic Principle. In this paper, we describe and apply a framework called Full Indexical Conditioning (FIC) for performing Bayesian inference in this situation. Inspired by, but distinct from, Full Non-Indexical Conditioning, FIC conditions on all evidence available to the reasoner while considering that this evidence could have been otherwise. We address the reference class problem associated with such reasoning, demonstrating that substantive conclusions are unaffected by the choice of reference class provided it is sufficiently large. We apply FIC to several problems in astrobiology, including the Doomsday argument, the early abiogenesis time, and our location around a G-type rather than M-type star, clarifying the foundations of these arguments. We conclude that the early abiogenesis time does not rule out pessimistic possibilities for life's abundance, and that while life around M stars may be uncommon, its temporal distribution could extend far into the future. Ultimately, FIC offers a clear conceptual framework, grounded in straightforward probability theory, for tackling problems involving anthropic selection effects.

astro-ph.IM↗

arXiv2026

The Radius-Luminosity Relationship for Active Galactic Nuclei with Hierarchical Bayesian Reverberation Mapping

Reverberation mapping of active galactic nuclei uses the time taken for variability to travel through the system as a measure of system size, with this size being used to inform estimates of the mass of the central black hole, a technique that has graduated to an industrial-scale effort in recent decades. Such large target-count, multi-year surveys have been consistently undercut by poor light curve quality and the aliasing problems of seasonal observations. These impacts compound with statistical approaches that are not consistent between works and sometimes combine inconsistent statistical frameworks. Here, we present a new end-to-end Bayesian framework for fitting lags at scale in large surveys, simultaneous with the fitting of population models such as the radius-luminosity relation, and formulated in a numerically tractable way. This procedure is a statistically and numerically robust generalisation of the stacking and quality cut procedures of past works, fully marginalising over data uncertainty and data quality. Our approach remains numerically stable when scaling to larger surveys, and can act as a basis for any Bayesian population modelling of large sets of AGN time series observations. Applied to the OzDES sample, we demonstrate that this new approach yields more than double the constraining power on population-level properties like the R-L relationship, and an order-of-magnitude increase in the number of recovered lags and masses. With this method, we go from 24 high quality lag recoveries with traditional methods to a new effective sample size of ~297, all while being robust against random chance false positive measurements.

astro-ph.GA↗

arXiv2026

Life in the Cosmic Neighbourhood: Galactic Habitable Zones in the EAGLE Simulations

When and where is life most likely to form in the universe? We use the EAGLE cosmological hydrodynamical simulations to investigate the prevalence and properties of life-friendly cosmic environments on galactic scales. Our model for the occurrence of observers depends on main-sequence stars, the production and distribution of metals, and the formation of habitable planets. We also take into account five potentially life-extinguishing processes: core-collapse supernovae, Type Ia supernovae, star-star interactions, gamma ray bursts and quasars. We characterise the amount of time that the universe creates on habitable planets per unit mass of baryons and stars in the universe, as a function of galaxy mass and galactocentric distance. As expected, early universe, newly formed, high star formation rate galaxies are the most dangerous. The present-day Milky Way is typical of habitable galaxies: efficient creation of habitable time, and low probability of cosmic catastrophes.

astro-ph.GA↗

arXiv2026

A near-IR survey of luminous asymptotic giant branch stars in the satellites and stellar halo of M31

We investigate the dwarf spheroidal (dSph) satellites and stellar halo of M31 using near-infrared imaging from the Wide-Field Camera on the UKIRT 3.8 m telescope. Our homogeneous analysis covers the stellar extents of 12 dSphs, as well as their surrounding halo field populations. We identify carbon-rich (C) and oxygen-rich (M) thermally-pulsing AGB stars (TP-AGBs) using colour-magnitude and colour-colour diagrams, which also allows for effective contaminant rejection. TP-AGB stars are detected in eight of the 12 dSphs, indicating small intermediate-age populations in a substantial fraction of the sample; they are also found in considerable numbers throughout most of M31's stellar halo. By combining 316 new detections with a revised classification of objects previously reported in the literature, we increase the TP-AGB candidate population in the dSphs from 82 to 359. We use the resulting dSph and halo AGB samples to compute C/M ratios and infer metallicities in the dSphs and adjacent halo fields with non-zero AGB counts. A clear metallicity gradient is observed in the M31 stellar halo out to ~150 kpc, consistent with that found using other tracers. Using literature star formation histories from main-sequence turn-off photometry, we find a tight correlation between the number of C stars in the dSphs and the stellar mass formed in the last 0.5--3 Gyr. This study underscores the promise of AGB stars as quantitative tracers of intermediate-age star formation, particularly in intrinsically faint systems, and provides a catalogue of candidate TP-AGB stars for follow-up.

astro-ph.GA↗

arXiv2026

Harnessing stellar kinematics to constrain dark energy with the double-source-plane gravitational lens SDSS J0946+1006

SDSS J0946+1006 is an attractive target for measuring cosmological parameters through lens modelling. It is the best-studied galaxy-scale strong gravitational lens with multiple sources whose redshift separations are well-suited to constraining the dark energy equation of state. However, multi-plane lens models with free cosmological parameters risk a multi-plane mass-sheet degeneracy, although this can be lifted by a non-lensing deflector density profile tracer. We simultaneously reconstruct near-infrared and near-ultraviolet HST imaging whilst including a velocity dispersion measurement from VLT-MUSE to constrain the foreground deflector. Imaging is reconstructed faithfully regardless of whether the inferred kinematics are realistic, though we find the kinematic constraint essential for shifting the preferred cosmology into a region not in significant tension with other dark energy probes. Deflector density profile perturbations, via substructure and multipolar halo shape deformations, have only a modest effect on inferred cosmology. Combining our fiducial model with Planck CMB data yields $w=-1.01^{+0.08}_{-0.13}$; or, combined with Pantheon SNe Ia, $w=-0.99^{+0.13}_{-0.15}$. We further show that this system proves a remarkably valuable complementary probe in the $w_{0}$-$w_{a}$ plane of an evolving dark energy model, and that the DESI BAO tension with $Λ$CDM seen when combined with other datasets is not reproduced when combined with this lens, yielding $(w_{0}, w_{a})=(-0.87^{+0.10}_{-0.11}, -0.22^{+0.28}_{-0.25})$. The system's third source, visible with MUSE, only weakly constrains $w$CDM but may strengthen $w_{0}w_{a}$CDM constraints, though further mass-model complexity along its line of sight is required. Overall, kinematics-informed multi-plane lens modelling is a robust route to competitive dark energy constraints, even with a single system.

astro-ph.CO↗

arXiv2026

Algorithmic bottlenecks in evolution: Genetic code, symbolic language, and the Great Filter hypothesis

The Great Filter hypothesis proposes that the emergence of technological societies capable of interstellar travel depends on a small number of exceptionally hard and highly improbable steps. Traditional versions of this hypothesis enumerate such "hard steps" along the trajectory from inanimate matter to complex technological societies but diverge in their explanations for why these particular steps should be so improbable. The theory of Major Evolutionary Transitions also faces challenges in identifying which steps should be considered universally "hard" across different evolutionary pathways. In contrast, we argue that two deeply structural obstacles dominate the evolutionary landscape: the coding threshold associated with the origin of genetic code, and the language threshold associated with the emergence of symbolic communication. We examine the developmental precursors of both transitions and analyze the underlying algorithmic bottlenecks: points at which evolving systems separate code from function, while entangling them within information hierarchies. Using a game-theoretic analysis of coupled signaling and coordination dynamics, we then argue that the corresponding multichannel games may exhibit saddle-type equilibria whose stable manifolds define narrow evolutionary paths, making the transitions intrinsically difficult to traverse. We conjecture that the so-called Great Filter is best understood not as a sequence of isolated improbable events, but as a nested structure of tangled information hierarchies. Under this conjecture, the rarity of advanced societies follows from the difficulty of crossing these coding thresholds in a competitive noisy environment. This hypothesis reframes the Great Filter as an algorithmic property of evolving systems, suggesting that only a small fraction of life may ever traverse the path toward technological societies capable of interstellar travel.

q-bio.PE↗

arXiv2026

$S^5$: Tidal Disruption in Crater 2 and Formation of Diffuse Dwarf Galaxies in the Local Group

We present results of a spectroscopic campaign around the diffuse dwarf galaxy Crater 2 (Cra2) and its tidal tails as part of the Southern Stellar Stream Spectroscopic Survey ($S^5$). Cra2 is a Milky Way dwarf spheroidal satellite with extremely cold kinematics, but a huge size similar to the Small Magellanic Cloud, which may be difficult to explain within collisionless cold dark matter. We identify 143 Cra2 members, of which 114 belong to the galaxy's main body and 29 are deemed part of its stellar stream. We confirm that Cra2 is dynamically cold (central velocity dispersion $2.51^{+0.33}_{-0.30}\,{\rm km \ s^{-1}}$) and also discover a $\approx$7$σ$ velocity gradient consistent with its tidal debris track. We separately estimate the stream's internal velocity dispersion to be $5.74^{+0.98}_{-0.83}\,{\rm km \ s^{-1}}$. We develop a suite of $N$-body simulations with both cuspy and cored density profiles on a realistic Cra2 orbit to compare with $S^5$ observations. We find that the velocity dispersion ratio between Cra2 stream and galaxy ($2.30^{+0.41}_{-0.35}$) is difficult to reconcile with a cuspy halo with fiducial concentration and an initial mass predicted by standard stellar mass--halo mass relationships. Instead, either a cored halo with relatively small core radius or a low-concentration cuspy model can reproduce this ratio. Despite tidal mass loss, Cra2 is metal-poor ($\langle \rm[Fe/H]\rangle=-2.16\pm0.04$) compared to the stellar mass--metallicity relation for its luminosity. Other diffuse dwarf galaxies similar to Cra2 in the Local Group (Antlia 2 and Andromeda 19) also challenge galaxy formation models. Finally, we discuss possible formation scenarios for Cra2, including ram-pressure stripping of a gas-rich progenitor combined with tides.

astro-ph.GA↗

arXiv2026

The GALAH Survey: Neutron-Capture Elemental Abundances for 350,000 Gaia-RVS spectra and the Chemodynamics of Accreted Structures

We present a comprehensive data-driven spectroscopic analysis of 357,415 red giant stars using Gaia DR3 Radial Velocity Spectrometer (RVS) spectra (8460-8700 A; $R\approx11,500$), aimed at deriving homogenous stellar parameters and elemental abundances (collectively referred to as stellar labels). We employ The Cannon, a generative model based on 2747 giants in common with GALactic Archaeology with HERMES (GALAH) DR4, adopting GALAH labels ($R\approx28,000$) for training. The resulting model predicts 11 stellar labels for RVS giants: effective temperature ($T_{\rm eff}$), surface gravity ($\log g$), projected rotational velocity ($v\sin i$), and abundances of [Fe/H], [Ca/Fe], [Si/Fe], [Ni/Fe], [Ti/Fe], as well as the neutron-capture elements [Zr/Fe], [Ce/Fe], and [Nd/Fe]. Building on these results, we develop a probabilistic framework to chemically identify debris from the Gaia-Sausage-Enceladus (GSE) accretion event. A logistic regression classifier, optimized via Markov chain Monte Carlo sampling and trained on a small reference sample of GSE members and comparison stars, identifies stars with high GSE membership probabilities based solely on their chemical abundances, with the resulting candidates exhibiting distinctive abundance-ratio patterns, including [Ca/Ti], [Ti/Ce], and [Nd/Zr]. Applying independent kinematic constraints yields a robust sample of GSE candidates, demonstrating that the characteristic chemical signatures remain consistent after applying these constraints. This work demonstrates the potential of data-driven analysis techniques to extract detailed chemical information from medium-resolution spectra and establishes a framework for tracing Galactic accretion events using chemical abundances.

astro-ph.GA↗

arXiv2026

Simulation-based tension quantification of the cosmic dipole

The cosmic dipole measured in surveys of cosmologically distant sources consistently exceeds the expectation derived from the cosmic microwave background, posing a significant challenge to the standard $Λ$CDM cosmology. In the era of precision cosmology, quantifying robust tensions is constrained by our ability to model complex, non-linear effects that often result in intractable likelihood functions. In this paper, we present a flexible simulation-based inference (SBI) architecture for measuring the cosmic dipole tension using Neural Ratio Estimators (NREs). We design and train an ensemble of NREs to evaluate the log Bayesian evidence ratio and measure $Nσ$ tension. We validate our approach against nested sampling, demonstrating that it accurately recovers the ground-truth. Under the kinematic interpretation of the dipole, we apply our approach to Planck, the NRAO VLA Sky Survey (NVSS), the Rapid ASKAP Continuum Survey (RACS), and the Wide-field Infrared Survey Explorer catalogue (CatWISE). Here, leveraging SBI, we measure a $\approx5.7σ$ tension between CatWISE and Planck. We demonstrate the extensibility of our approach by applying it to forward-modelled simulations of the CatWISE Eddington bias, revealing a $\approx6.7σ$ tension. The methodology proposed here enables robust tension quantification as we enter the era of LSST, Euclid, and the SKA.

astro-ph.CO↗

arXiv2026

Microlensing of Microlensing: Effects of Random Stars on the Double-Source-Plane Gravitational Lens

Microlensing, the influence of stars within a galactic gravitational lens, has emerged as a powerful probe of compact mass and, through differential magnification, sub-parsec scale sources at cosmological distances. The recent discovery of a double-source-plane gravitational lens system in which the most distant source is a quasar offers the prospect of compound microlensing, in which quasar light rays are influenced by compact masses within the two foreground lensing galaxies. Here, we present the first numerical simulations of this "microlensing of microlensing". We consider the recently discovered "Einstein zig-zag" lens, J1721+8842, as a fiducial case, and construct microlensing magnification maps for each of the six quasar images in this system. Due to the secondary microlensing effects of the myriad of initial microimages, the resulting maps contain more complex caustic features than seen in the case of single plane microlensing. This is reflected in the expected lightcurves seen for each of the images.

astro-ph.CO↗

arXiv2026

Boötes III is a Tidally Disrupting Ultra-Faint Dwarf Galaxy on an Eccentric Polar Orbit

We present updated systemic properties of the ultra-faint dwarf galaxy Boötes III from the Southern Stellar Stream Spectroscopic Survey (S$^5$). We identify 21 high-probability members and measure a velocity dispersion of $σ_{v} = 1.69^{+1.03}_{-0.85}$ km s$^{-1}$, about six times smaller than the previously reported $10.7 \pm 3.5$ km s$^{-1}$, and a mean metallicity of [Fe/H] $= -2.34 \pm 0.11$. The revised dispersion brings Boötes III in line with other tidally disrupting dwarfs such as Antlia II and Crater II. Orbit integrations in a Milky Way (MW) + Large Magellanic Cloud (LMC) potential confirm a highly eccentric ($e \approx 0.8$), polar ($i \approx 89.5^\circ$) orbit with a recent pericentric passage $\sim 0.14$ Gyr ago at $r_{\rm peri} \approx 9.5$ kpc. Boötes III is thus likely actively tidally disrupting, as its tidal radius at pericenter, $r_t \approx 164$ pc, is only $\sim 0.35$ of its half-light radius. The unusually low dispersion also implies that Boötes III has either lost most of its dark matter to tides or hosts a cored inner density profile, making it a probe of the nature of dark matter. Simulated tidal streams are broadly consistent with the Styx stellar stream, though the predicted track and kinematics are sensitive to the MW halo mass, LMC mass, and solar velocity. Boötes III overlaps the Typhon stream in integrals-of-motion space but has a much lower mean metallicity, suggesting the two are not the same system but may have had a common group infall origin. Sagittarius-stream contamination prevents a direct tidal-tail detection, so deep spectroscopic follow-up remains essential, both to confirm Styx as a genuine stream and to establish it as Boötes III's tidal tail.

astro-ph.GA↗

arXiv2026

The twin paradox in the vicinity of rotating black holes

The twin paradox is a foundational thought experiment in the special theory of relativity where a returning twin ages less than the one who remains stationary. However, the intricacies of the twin paradox remain relatively underexplored in the curved spacetimes of general relativity. Here we explore the twin paradox in the vicinity of a rotating black hole, where the existence of multiple paths between two events creates significant complexity. We develop a numerical framework based on residual maps and optimisation to identify possible trajectories. We find a strong negative correlation between a traveller's experienced proper time and both the azimuthal distance travelled and the magnitude of acceleration. We apply numerical Jacobi field analysis to examine conjugate points along geodesics within the Kerr geometry, finding that only the geodesic with the minimal azimuthal distance contains no conjugate points. This provides beginner students of general relativity with a visual tool to understand general relativistic concepts, helping to correct flat-spacetime intuitions.

gr-qc↗

arXiv2026

The Information Content of Quasar Variability Light Curves: How Well Can we Infer Stochastic Model Parameters?

Quasar variability, driven by multi-scale physical processing within a relativistic accretion disk, is commonly modelled with stochastic time series models. The simplest of these is the Damped Random Walk (DRW), also known as the Ornstein-Uhlenbeck (OU) process. Here, we demonstrate that, when fitting such a model to quasar light curve data, the mean of the light curve, $μ$, should not be fixed (which is the typical approach), as this leads to overconfident inferences about the variability timescale $τ$, with substantially underestimated uncertainties. However, the short term volatility parameter $η$ is typically very well constrained from short light curves. Through simulations, we compute information theoretic quantities such as the conditional entropy and the mutual information, confirming that light curves provide much more information about $η$ than about $τ$. As a result, we recommend that future quasar variability studies focus on $η$ rather than $τ$. To demonstrate this approach, we fit a hierarchical Bayesian regression model for $η$ as a function of bolometric luminosity and rest wavelength to a dataset of 570 light curves measured over decades. We perform the fit using a likelihood function that uses the light curves directly, rather than using intermediate $η$ values from individual light curve fits. We find that volatility decreases as a function of both bolometric luminosity and rest wavelength. The volatility also decreases more steeply with redshift than time dilation alone would suggest, pointing to an increase in intrinsic volatility as quasars evolve over cosmic time.

astro-ph.GA↗

arXiv2026

The Ellis and Baldwin test of the Cosmic Dipole: Exploring the impact of multiple flux density cuts

The cosmic dipole tension - the discrepancy between the Cosmic Microwave Background kinematic dipole and the matter dipole inferred from all-sky surveys poses a significant challenge to the Cosmological Principle, which dictates that the universe is homogeneous and isotropic at the largest scales. Traditional measurement of the matter dipole requires selecting an appropriate limiting flux and calculating the dipolar modulation using sources brighter than the flux. This approach, however, ignores the shape of the source luminosity function (LF) and deprives the analysis of this crucial information. In this study, we present a new approach to calculate the matter dipole by integrating the source flux distribution into the analysis. We achieve this by dividing the catalogue into disjoint flux bins and simultaneously fitting the matter dipole across them. For non-power-law LFs, this method gives a higher Bayes factor - and hence a better description of the matter dipole - as compared to the traditional approach. The method works best when the flux cuts are selected in regions where the LF's shape changes significantly. We discuss the feasibility of this method for upcoming cosmological surveys and show that it has the potential to yield decisive results at both radio and infrared wavelengths.

astro-ph.CO↗

arXiv2026

Cosmic dipole tensions: confronting the cosmic microwave background with infrared and radio populations of cosmological sources

The cosmic dipole measured in surveys of cosmologically distant sources is generally found to be in disagreement with the kinematic expectation of the Cosmic Microwave Background (CMB). This discrepancy represents severe tension with the Cosmological Principle and challenges the standard model of cosmology. Here, we present a Bayesian analysis of the tension between datasets used to measure the cosmic dipole. We examine the NRAO VLA Sky Survey (NVSS), the Rapid ASKAP Continuum Survey (RACS) and the Wide-field Infrared Survey Explorer catalogue (CatWISE), and jointly analyse them with the Planck observations of the CMB. Under the kinematic interpretation, we find that Planck is in severe tension with CatWISE above 5$σ$, strong tension with RACS, and moderate tension with NVSS. Moreover, the strong concordance between CatWISE and NVSS suggests that their dipoles arise from a common astrophysical signal. Conversely, the high discordance between RACS and both CatWISE and NVSS indicates a possible systematic difference in the RACS catalogue itself. Whilst the tension between Planck and infrared-selected quasars is already significant, the question of whether or not the dipole in individual radio surveys adds to the challenge against the standard model is yet to be seen. We estimate that $\mathcal{O}(10^6)$ radio sources are required to measure the tension to a significance of 5$σ$. Therefore, in light of the upcoming SKA radio surveys, we are on the cusp of disentangling the anomaly of the cosmic dipole.

astro-ph.CO↗