arXiv subjects

C. T. Davies

Publications and source records attributed to C. T. Davies.

9 recordsLinked to original sources

arXiv2026

The correlation between voids identified in 3D large-scale-structure and 2D weak-lensing maps

We investigate the correspondence between voids identified in the 3D halo distribution and those detected in WL convergence maps. We used 108 realizations of the full-sky lensing simulations, populated with a source galaxy redshift distribution consistent with the Dark Energy Survey Year 3 sample. Catalogs of 3D halo voids and WL voids were constructed using the VIDE and tunnel algorithms, respectively. The spatial association between the two populations was quantified by measuring the angular excess number density of halo voids around WL void centers. We detected a statistically significant (S/N >= 25) positive correlation between WL voids and low-redshift halo voids (0 < z_hv < 0.5) at small angular separations, indicating that WL voids trace genuine underdensities in the large-scale matter distribution. The correlation amplitude closely depends on the WL void selection scheme and decreases when stringent peak-amplitude thresholds are applied, thereby reducing the number of detected WL voids and broadening their effective sizes. The signal also displays a strong redshift dependence: halo voids at higher redshift exhibit weaker correlations because of the declining efficiency of the WL kernel, while WL voids identified from higher-redshift source bins produce stronger correlations due to the increased contribution from line-of-sight structures. We additionally examined the impact of halo-void morphology and found that rounder voids with a weaker alignment along the line of sight display marginally stronger associations with WL voids. Our results provide new insights into the contribution of 3D structure to WL-selected underdensities and offer guidance for future observational analyses seeking to interpret WL voids as tracers of the matter field.

astro-ph.CO↗

arXiv2026

Constraints on the normal branch of DGP gravity from SPT galaxy clusters with DES and HST weak-lensing mass calibration and from Planck PR4 CMB anisotropies

We present constraints on the normal branch of the Dvali-Gabadadze-Porrati (nDGP) braneworld gravity model from the abundance of massive galaxy clusters. On scales below the nDGP crossover scale $r_{\rm c}$, the nDGP model features an effective gravity-like fifth force that alters the growth of structure, leading to an enhancement of the halo mass function (HMF) on cluster scales. The enhanced cluster abundance allows for constraints on the nDGP model using cluster samples. We employ the SPT cluster sample, selected through the thermal Sunyaev-Zel`dovich effect (tSZE) with the South Pole Telescope (SPT) and with mass calibration using weak-lensing data from the Dark Energy Survey (DES) and the Hubble Space Telescope (HST). The cluster sample contains 1,005 clusters with redshifts $0.25 < z < 1.78$, which are confirmed with the Multi-Component Matched Filter (MCMF) algorithm using optical and near-infrared data. Weak-lensing data from DES and HST enable a robust mass measurement of the cluster sample. We use DES Year 3 data for 688 clusters with redshifts $z < 0.95$, and HST data for 39 clusters with redshifts $ 0.6 < z <1.7$. We account for the enhancement in the HMF through a semi-analytic correction factor to the standard cosmology HMF derived from the spherical collapse model in the nDGP model. We then further calibrate this model using $N$-body simulations. In addition, for the first time, we analyze the primary cosmic microwave background (CMB) temperature and polarization anisotropy measurements from Planck PR4 within the nDGP model. We obtain a competitive constraint from the joint analysis of the SPT cluster abundance with the Planck PR4 data, and report an upper bound of $1/\sqrt{(H_0r_{\rm c})}< 1.41$ at $95\,\%$ when assuming a cosmology with massive neutrinos.

astro-ph.CO↗

arXiv2026

On the cosmology dependence of the cluster weak-lensing mass bias

Measurements of the shear induced by weak gravitational lensing around galaxy cluster lines of sight are the gold standard for calibrating cluster observable-mass relations, thereby enabling a robust and precise inference of cosmological parameters. The weak-lensing mass bias is the systematic offset between the true halo mass and the mass that is inferred from the lensing data using an imperfect model for the halo mass distribution. We study the impact of cosmology on the lensing mass bias to inform future cosmological analyses of galaxy clusters. We create synthetic lensing shear maps for 115,920 projections of clusters with $M_{200\mathrm c}>1.56\times10^{14}\,h^{-1}M_\odot$ in a suite of Magneticum simulations. The simulation boxes are $896\,h^{-1}$Mpc on a side and are set up with 15 different combinations of the cosmological parameters $Ω_\mathrm{m}$, $Ω_\mathrm{b}$, $σ_8$, and $H_0$. Assuming a Navarro-Frenk-White profile, we extract weak-lensing mass measurements and quantify their bias $b_\mathrm{WL}$ with respect to the true halo mass. To investigate the impact of baryonic effects, we perform the analysis on gravity-only simulations and on their full-physics hydrodynamical counterparts. We confirm that assuming a fixed halo concentration or a fixed concentration-mass relation leads to cosmology-dependent changes of the mass bias. We report changes of up to $Δ\ln b_\mathrm{WL}=0.030$ with respect to the bias obtained at the fiducial WMAP7 cosmology. Adopting a model for the concentration that also depends on cosmology absorbs the changes in halo profiles and we recover essentially constant values for the mass bias. Our analysis of hydrodynamical simulations suggests that future, more accurate models will also need to explicitly account for the strength of baryonic effects.

astro-ph.CO↗

arXiv2025

Tracing cosmic voids with fast simulations

Context. Cosmic voids are vast underdense regions in the cosmic web that encode crucial information about structure formation, the composition of the Universe, and its expansion history. Due to their lower density, these regions are less affected by non-linear gravitational dynamics, making them suitable candidates for analysis using semi-analytic methods. Aims. We assess the accuracy of the PINOCCHIO code, a fast tool for generating dark matter halo catalogs based on Lagrangian Perturbation Theory, in modeling the statistical properties of cosmic voids. We validate this approach by comparing the resulting void statistics measured from PINOCCHIO to those obtained from N-body simulations. Methods. We generate a set of simulations using PINOCCHIO and OpenGADGET3, assuming a fiducial cosmology and varying the resolution. For a given resolution, the simulations share the same initial conditions between the different simulation codes. Snapshots are saved at multiple redshifts for each simulation and post-processed using the watershed void finder VIDE to identify cosmic voids. For each simulation code, we measure the following statistics: void size function, void ellipticity function, core density function, and the void radial density profile. We use these statistics to quantify the accuracy of PINOCCHIO relative to OpenGADGET3 in the context of cosmic voids. Results. We find agreement for all void statistics at better than 2σ between PINOCCHIO and OpenGADGET3, with no systematic difference in redshift trends. This demonstrates that the PINOCCHIO code can reliably produce void statistics with high computational efficiency compared to full N-body simulations.

astro-ph.CO↗

arXiv2025

Cosmic Tunnels and the Integrated Sachs-Wolfe effect

Cosmic voids, vast underdensities in the large-scale structure, offer unique sensitivity to cosmological parameters. However, traditional 3D galaxy-based void finding is limited by many factors, including uncertainties in the galaxy-halo connection and distortions from redshift errors. Using alternative tracers and new 2D void definitions can alleviate these limitations and be tailored to maximise the signal for specific observables. Here, we introduce Cosmic Tunnels, a new class of 2D void-like objects traced by galaxy clusters, corresponding to large underdense lines of sight. We identify Cosmic Tunnels by applying the tunnel algorithm to the RASS-MCMF and ACT-MCMF cluster catalogues. We validate their void-like nature by measuring the cross-correlation of Cosmic Tunnels with galaxy density contrast maps from the DESI Legacy Survey (measured at 63$σ$ significance), galaxy weak-lensing maps from DES Y3 (31$σ$), and CMB weak-lensing maps from ACT DR6 (15$σ$), all of which show underdense interiors enclosed by compensation ridges, consistent with 3D galaxy voids, measured at high statistical significance. We also show that the lensing profiles fit the universal HSW void profile, further validating their void-like nature. We cross-correlate the Cosmic Tunnels with Planck CMB temperature maps to measure the ISW signal. Using the ACT-MCMF Cosmic Tunnels, we achieve a 3.6$σ$ ISW detection, one of the highest significances ever reported from a single tracer catalogue. These results confirm that Cosmic Tunnels are robust underdense structures and demonstrate their potential as a new tool for cosmological analyses. Finally, we report a tentative detection of a sign flip in the ISW signal at very low redshift (z<0.03), consistent with previous studies, challenging the standard $Λ\rm{CDM}$ paradigm.

astro-ph.CO↗

arXiv2025

Non-linear infusion of intrinsic alignment and source clustering: impact on non-Gaussian cosmic shear statistics

Intrinsic alignments (IA) of galaxies is one of the key secondary signals to cosmic shear measurements, and must be modeled to interpret weak lensing data and infer the correct cosmology. There are large uncertainties in the physical description of IA, and analytical calculations are often out of reach for weak lensing statistics beyond two-point functions. We present here a set of six flexible IA models infused directly into weak lensing simulations, constructed from the mass shells, the projected tidal fields and, optionally, dark matter halo catalogues. We start with the non-linear linear alignment (NLA) and progressively sophisticate the galaxy bias and the tidal coupling models, including the commonly-used extended NLA (also known as the e-NLA or $δ$-NLA) and the tidal torque (TT) models. We validate our methods with MCMC analyses from two-point shear statistics, then compute the impact on non-Gaussian cosmic shear probes from these catalogues as well as from reconstructed convergence maps. We find that the $δ$-NLA model has by far the largest impact on most probes, at times more than twice the strength of the NLA. We also observe large differences between the IA models in under-dense regions, which makes minima, void profiles and lensing PDF the best probes for model rejection. Furthermore, our bias models allow us to separately study the source-clustering term for each of these probes, finding good agreement with the existing literature, and extending the results to these new probes. The third-order aperture mass statistics ($M^3_{ap}$) and the integrated three-point functions are particularly sensitive to this when including low-redshift data, often exceeding a 20% impact on the data vector. Our IA models are straightforward to implement and rescale from a single simulated IA-infused galaxy catalogue, allowing for fast model exploration.

astro-ph.CO↗

arXiv2025

Euclid: Early Release Observations of ram-pressure stripping in the Perseus cluster. Detection of parsec scale star formation with in the low surface brightness stripped tails of UGC 2665 and MCG +07-07-070

Euclid is delivering optical and near-infrared imaging data over 14,000 deg$^2$ on the sky at spatial resolution and surface brightness levels that can be used to understand the morphological transformation of galaxies within groups and clusters. Using the Early Release Observations (ERO) of the Perseus cluster, we demonstrate the capability offered by Euclid in studying the nature of perturbations for galaxies in clusters. Filamentary structures are observed along the discs of two spiral galaxies with no extended diffuse emission expected from tidal interactions at surface brightness levels of $\sim$ $30\,{\rm mag}\,{\rm arcsec}^{-2}$. The detected features exhibit a good correspondence in morphology between optical and near-infrared wavelengths, with a surface brightness of $\sim$ $25\,{\rm mag}\,{\rm arcsec}^{-2}$, and the knots within the features have sizes of $\sim$ 100 pc, as observed through $I_E$ imaging. Using the Euclid, CFHT, UVIT, and LOFAR $144\,{\rm MHz}$ radio continuum observations, we conduct a detailed analysis to understand the origin of the detected features. We constructed the \textit{Euclid} $I_E-Y_E$, $Y_E-H_E$, and CFHT $u - r$, $g - i$ colour-colour plane and showed that these features contain recent star formation events, which are also indicated by their H$α$ and NUV emissions. Euclid colours alone are insufficient for studying stellar population ages in unresolved star-forming regions, which require multi-wavelength optical imaging data. The morphological shape, orientation, and mean age of the stellar population, combined with the presence of extended radio continuum cometary tails can be consistently explained if these features have been formed during a recent ram-pressure stripping event. This result further confirms the exceptional qualities of Euclid in the study of galaxy evolution in dense environments.

astro-ph.GA↗

arXiv2025

Constraints on $f(R)$ gravity from tSZE-selected SPT galaxy clusters and weak lensing mass calibration from DES and HST

We present constraints on the $f(R)$ gravity model using a sample of 1,005 galaxy clusters in the redshift range $0.25 - 1.78$ that have been selected through the thermal Sunyaev-Zel'dovich effect (tSZE) from South Pole Telescope (SPT) data and subjected to optical and near-infrared confirmation with the Multi-component Matched Filter (MCMF) algorithm. We employ weak gravitational lensing mass calibration from the Dark Energy Survey (DES) Year 3 data for 688 clusters at $z < 0.95$ and from the Hubble Space Telescope (HST) for 39 clusters with $0.6 < z < 1.7$. Our cluster sample is a powerful probe of $f(R)$ gravity, because this model predicts a scale-dependent enhancement in the growth of structure, which impacts the halo mass function (HMF) at cluster mass scales. To account for these modified gravity effects on the HMF, our analysis employs a semi-analytical approach calibrated with numerical simulations. Combining calibrated cluster counts with primary cosmic microwave background (CMB) temperature and polarization anisotropy measurements from the Planck2018 release, we derive robust constraints on the $f(R)$ parameter $f_{R0}$. Our results, $\log_{10} |f_{R0}| < -5.32$ at the 95 % credible level, are the tightest current constraints on $f(R)$ gravity from cosmological scales. This upper limit rules out $f(R)$-like deviations from general relativity that result in more than a $\sim$20 % enhancement of the cluster population on mass scales $M_\mathrm{200c}>3\times10^{14}M_\odot$.

astro-ph.CO↗

arXiv2025

Galaxy cluster matter profiles: I. Self-similarity, mass calibration, and observable-mass relation validation employing cluster mass posteriors

We present a study of the weak lensing inferred matter profiles $ΔΣ(R)$ of 698 South Pole Telescope thermal Sunyaev-Zel'dovich effect selected and MCMF optically confirmed galaxy clusters in the redshift range $0.25 <z< 0.94$ that have associated weak gravitational lensing shear profiles from the Dark Energy Survey. Rescaling these profiles to account for the mass dependent size and the redshift dependent density produces average rescaled matter profiles $ΔΣ(R/R_\mathrm{200c})/(ρ_\mathrm{crit}R_\mathrm{200c})$ with a lower dispersion than the unscaled $ΔΣ(R)$ versions, indicating a significant degree of self-similarity. Galaxy clusters from hydrodynamical simulations also exhibit matter profiles that suggest a high degree of self-similarity, with RMS variation among the average rescaled matter profiles with redshift and mass falling by a factor of approximately six and 23, respectively, compared to the unscaled average matter profiles. We employed this regularity in a new Bayesian method for weak lensing mass calibration that employs the so-called cluster mass posterior $P(M_\mathrm{200c}|\hatζ, \hatλ, z)$, which describes the individual cluster masses given their tSZE and optical observables. We validated the method using realistic mock datasets and present observable-mass relation constraints for the SPT$\times$DES sample. We present new validation tests of the observable-mass relation that indicate the underlying power-law form and scatter are adequate to describe the real cluster sample but that also suggest a redshift variation in the intrinsic scatter of the $λ$-mass relation may offer a better description. In addition, the average rescaled matter profiles offer high signal-to-noise ratio constraints on the shape of real cluster matter profiles, which are in good agreement with available hydrodynamical $Λ$CDM simulations.

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