arXiv subjects

Erwin T. Lau

Publications and source records attributed to Erwin T. Lau.

At least 19 recordsLinked to original sources

arXiv2026

Non-Thermal Pressure due to Gas Motions in the Intracluster Medium: Confronting XRISM/Resolve with TNG-Cluster Simulations

Intracluster medium (ICM) gas motions probe cluster assembly, feedback, and non-thermal pressure support, but recent XRISM observations reveal velocity dispersions and non-thermal pressure fractions systematically lower than simulations predict, with extreme systems such as Abell 2029 falling below nearly all simulated clusters. Using the TNG-Cluster simulations, we show that the non-thermal pressure fraction depends sensitively on cool-core state and formation history, and provide a two-scale fitting function capturing both the inner cool-core suppression and outer rise of the radial profile. By forward-modeling mock XRISM observations and comparing them with both projected and intrinsic three-dimensional quantities, we find that azimuthal variations and projection effects contribute to the deficit in the observed velocity dispersion and non-thermal pressure fraction. This bias increases with radius and partially offsets the intrinsic outward rise in the true three-dimensional non-thermal pressure fraction. However, these effects cannot explain the extremely low values of the non-thermal pressure fraction observed in Abell 2029, which fall below approximately the 0th-6th percentiles of the simulated cool-core cluster distribution at every measured radius under both the turbulence-only and turbulence-plus-bulk definitions. The remaining tension points to rare dynamical conditions or missing physics affecting the amplitude of gas motions in current ICM models.

astro-ph.CO↗

arXiv2026

Kinetic structure of the intracluster medium across nearby clusters observed with XRISM

XRISM/Resolve is building a sample of galaxy clusters with directly measured ICM gas motions, revealing diverse projected dynamical states. We compile 45 XRISM/Resolve measurements in 19 nearby galaxy clusters and place them on a common, emission-weighted effective line-of-sight scale, $\ell_{\rm eff}$. We compare the line-of-sight velocity dispersion $σ_v$, bulk velocity amplitude $|v_{\rm bulk}|$, their ratio $R_v \equiv |v_{\rm bulk}|/σ_v$, and non-thermal pressure proxies. Disturbed non-cool-core systems are not simply higher-dispersion counterparts of relaxed cool-core regions. Instead, differences among cool-core centers, cool-core outer regions, and non-cool-core systems are driven mainly by coherent line-of-sight motion relative to unresolved line broadening: $R_v$ tends to remain below unity in cool-core regions but often exceeds unity in non-cool-core systems, with the mean $R_v$ rising from 0.45 in cool-core centers to 1.6 in non-cool-core systems. These diagnostics help separate local central line broadening, likely associated with AGN feedback in some cool cores, from larger-scale coherent motions associated with sloshing, mergers, and halo assembly. Comparison with forward-modeled TNG-Cluster predictions suggests that many cool-core measurements occupy the lower part of the predicted non-thermal pressure range, consistent with small hydrostatic-mass corrections in relaxed systems and larger corrections in disturbed ones. XRISM is thus beginning to resolve the projected kinetic structure of the ICM across cluster environments, rather than tracing a single sequence of increasing turbulence.

astro-ph.CO↗

arXiv2026

XRISM reveals sloshing-driven gas motions in the core of Abell 2029

We investigate the velocity structure of the intracluster medium (ICM) in the core of the relaxed cool-core cluster Abell 2029 using XRISM Resolve spectroscopy. We analyze combined XRISM Resolve observations and divide the central region into several subregions. To account for photon mixing caused by the XRISM point spread function, we perform a spatial-spectral mixing analysis. We detect an ordered line-of-sight bulk-velocity gradient across the cluster core: the northern regions are blueshifted relative to the brightest cluster galaxy (BCG), while the southern regions are close to zero velocity or slightly redshifted. The maximum velocity difference is about $280~{\rm km\,s^{-1}}$. In contrast, the turbulent velocity dispersion is smaller, with measured values and upper limits of $\lesssim150~{\rm km\,s^{-1}}$, implying a non-thermal pressure fraction below $\sim2.5\%$. The velocity pattern is consistent with gas sloshing associated with the spiral structure seen in Chandra X-ray images. Averaged over all regions, the inferred turbulent heating rate is below the radiative cooling rate, indicating that turbulent dissipation alone is insufficient to offset cooling in the entire core. These results reveal that A2029 is not kinematically featureless: sloshing-induced bulk motions are present, while the observed line-of-sight velocity dispersion indicates only a limited contribution to pressure support and core heating.

astro-ph.HE↗

arXiv2026

Lensing-Reconstructed Dark Matter-Intracluster Medium Coherence as a Probe of Cluster Dynamical State: Application to HSTFF, RELICS, and CLASH Clusters

We present the first application of Fourier-space coherence analysis between the lensing-reconstructed projected mass distribution and the X-ray-emitting intracluster medium to a sample of 49 observed galaxy clusters. Using publicly available HST convergence maps from the Hubble Frontier Fields, CLASH, and RELICS programs, together with Chandra X-ray imaging, we measure the scale-dependent coherence between the dark-matter-dominated surface mass density and the hot baryonic gas. We use the coherence length, l_CR, defined as the scale above which the two maps remain at least 90% coherent, as a diagnostic of cluster dynamical state. Across the sample, dynamically relaxed systems exhibit high coherence over a broad range of scales and small l_CR/r500, while disturbed and merging systems show a loss of coherence on intermediate and small scales, yielding larger l_CR/r500. The inferred coherence lengths show sensitivity to lens-model assumptions and to the heterogeneous extent of the available convergence maps. Nevertheless, the coherence signal remains physically interpretable and provides a stringent measure of dark-matter-gas alignment. Applying a conservative threshold, l_CR/r500 < 0.2, we find that only 16% of the sample is relaxed; this fraction rises to 41% for a more permissive threshold of l_CR/r500 < 0.4. Relative to previous X-ray and morphological classifications, we find a 24% disagreement, with the coherence method identifying more systems as dynamically disturbed. These results demonstrate that lensing-X-ray coherence provides a complementary, scale-resolved probe of cluster dynamical state, while highlighting the need for homogeneous, wide-field weak-lensing maps to control reconstruction and field-of-view systematics.

astro-ph.CO↗

arXiv2025

Revisiting Galaxy Cluster Scaling Relations through Dark Matter-Gas Coherence: Scatter Dependence on Dynamical State

Galaxy clusters, the most massive, dark-matter-dominated, and most recently assembled structures in the Universe, are key tools for probing cosmology. However, uncertainties in scaling relations that connect cluster mass to observables like X-ray luminosity and temperature remain a significant challenge. In this paper, we present the results of an extensive investigation of 329 simulated clusters from Illustris TNG300 cosmological simulations. Our analysis involves cross-correlating dark matter and the hot X-ray-emitting gas, considering both the 3D and 2D projected distributions to account for projection effects. We demonstrate that this approach is highly effective in evaluating the dynamical state of these systems and validating the often-utilized assumption of hydrostatic equilibrium, which is key for inferring cluster masses and constructing scaling relations. Our study revisits both the X-ray luminosity-mass and X-ray temperature-mass scaling relations, and demonstrates how the scatter in these relations correlates with the clusters' dynamical state. We demonstrate that matter-gas coherence enables the identification of an optimal set of relaxed clusters, reducing scatter in scaling relations by up to 40%. This innovative approach, which integrates higher-dimensional insights into scaling relations, might offer a new path to further reduce uncertainties in determining cosmological parameters from galaxy clusters.

astro-ph.CO↗

arXiv2025

Cosmology and Astrophysics with the Diffuse eRASS1 X-ray Angular Power Spectrum

The recent tension in the value of the cosmological parameter $S_8 \equiv σ_8(Ω_M/0.3)^{1/2}$, which represents the amplitude of the matter density fluctuations of the universe, has not been resolved. In this work, we present constraints on $S_8$ with the X-ray angular power spectra of clusters and groups measured with the half-sky map from the eROSITA All Sky Survey data release 1 (eRASS1). Thanks to the extensive sky coverage of eRASS1, it achieves unprecedented precision compared to previous power spectrum measurements. Using a well-calibrated, physical halo gas model that includes astrophysics of feedback and non-thermal pressure support, we obtain $S_8 = 0.80^{+0.02}_{-0.01}$ with 1$σ$ uncertainty that is competitive against other cosmological probes. Our derived $S_8$ value is smaller than the primary CMB measurements from {\em Planck}, but still consistent to within $1σ$. We also obtain constraints on the astrophysics of feedback, non-thermal pressure, equation of state in cluster cores, and outer boundaries of gas in clusters and groups. We discuss how additional X-ray observations, and cosmological surveys in microwave and optical, will further improve the cosmological constraints with the angular power spectrum. Our work demonstrates that the angular power spectrum of clusters and groups is a promising probe of both cosmology and astrophysics.

astro-ph.CO↗

arXiv2025

X-raying CAMELS: Constraining Baryonic Feedback in the Circum-Galactic Medium with the CAMELS simulations and eRASS X-ray Observations

The circumgalactic medium (CGM) around massive galaxies plays a crucial role in regulating star formation and feedback. Using the CAMELS simulation suite, we develop emulators for the X-ray surface brightness profile and the X-ray luminosity--stellar mass scaling relation to investigate how stellar and AGN feedback shape the X-ray properties of the hot CGM. Our analysis shows that at CGM scales ($10^{12} \lesssim M_{\rm halo}/M_\odot \lesssim 10^{13}$, $10\lesssim r/{\rm kpc} \lesssim 400$), stellar feedback more significantly impacts the X-ray properties than AGN feedback within the parameters studied. Comparing the emulators to recent eROSITA All-Sky Survey observations, it was found that stronger feedback than currently implemented in the IllustrisTNG, SIMBA, and Astrid simulations is required to match observed CGM properties. However, adopting these enhanced feedback parameters causes deviations in the stellar-mass-halo-mass relations from observational constraints below the group mass scale. This tension suggests possible unaccounted systematics in X-ray CGM observations or inadequacies in the feedback models of cosmological simulations.

astro-ph.GA↗

arXiv2025

Baryon Pasting the Uchuu Lightcone Simulation

We present the Baryon Pasted (BP) X-ray and thermal Sunyaev-Zel'dovich (tSZ) maps derived from the half-sky Uchuu Lightcone simulation. These BP-Uchuu maps are constructed using more than $75$ million dark matter halos with masses $M_{500c} \geq 10^{13} M_\odot$ within the redshift range $0 \leq z \leq 2$. A distinctive feature of our BP-Uchuu Lightcone maps is their capability to assess the influence of both extrinsic and intrinsic scatter caused by triaxial gaseous halos and internal gas characteristics, respectively, at the map level. We show that triaxial gas drives substantial scatter in X-ray luminosities of clusters and groups, accounting for nearly half of the total scatter in core-excised measurements. Additionally, scatter in the thermal pressure and gas density profiles of halos enhances the X-ray and SZ power spectra, leading to biases in cosmological parameter estimates. These findings are statistically robust due to the extensive sky coverage and large halo sample in the BP-Uchuu maps. The BP-Uchuu maps are publicly available on https://app.globus.org/file-manager?origin_id=cf8dadb7-b6e9-4e2c-abc1-0813877efc13 .

astro-ph.CO↗

arXiv2024

Cosmological and Astrophysical Parameter Inference from Stacked Galaxy Cluster Profiles Using CAMELS-zoomGZ

We present a study on the inference of cosmological and astrophysical parameters using stacked galaxy cluster profiles. Utilizing the CAMELS-zoomGZ simulations, we explore how various cluster properties--such as X-ray surface brightness, gas density, temperature, metallicity, and Compton-y profiles--can be used to predict parameters within the 28-dimensional parameter space of the IllustrisTNG model. Through neural networks, we achieve a high correlation coefficient of 0.97 or above for all cosmological parameters, including $Ω_{\rm m}$, $H_0$, and $σ_8$, and over 0.90 for the remaining astrophysical parameters, showcasing the effectiveness of these profiles for parameter inference. We investigate the impact of different radial cuts, with bins ranging from $0.1R_{200c}$ to $0.7R_{200c}$, to simulate current observational constraints. Additionally, we perform a noise sensitivity analysis, adding up to 40\% Gaussian noise (corresponding to signal-to-noise ratios as low as 2.5), revealing that key parameters such as $Ω_{\rm m}$, $H_0$, and the IMF slope remain robust even under extreme noise conditions. We also compare the performance of full radial profiles against integrated quantities, finding that profiles generally lead to more accurate parameter inferences. Our results demonstrate that stacked galaxy cluster profiles contain crucial information on both astrophysical processes within groups and clusters and the underlying cosmology of the universe. This underscores their significance for interpreting the complex data expected from next-generation surveys and reveals, for the first time, their potential as a powerful tool for parameter inference.

astro-ph.CO↗

arXiv2024

Comparison of Models for the Warm-Hot Circumgalactic Medium around Milky Way-like Galaxies

A systematic comparison of the models of the circumgalactic medium (CGM) and their observables is crucial to understanding the predictive power of the models and constraining physical processes that affect the thermodynamics of CGM. This paper compares four analytic CGM models: precipitation, isentropic, cooling flow, and baryon pasting models for the hot, volume-filling CGM phase, all assuming hydrostatic or quasi-hydrostatic equilibrium. We show that for fiducial parameters of the CGM of a Milky-Way (MW) like galaxy ($\rm M_{vir} \sim 10^{12}~M_{\odot}$ at $z\sim 0$), the thermodynamic profiles -- entropy, density, temperature, and pressure -- show most significant differences between different models at small ($r\lesssim 30$ kpc) and large scales ($r\gtrsim 100$ kpc) while converging at intermediate scales. The slope of the entropy profile, which is one of the most important differentiators between models, is $\approx 0.8$ for the precipitation and cooling flow models, while it is $\approx0.6$ and 0 for the baryon pasting and isentropic models, respectively. We make predictions for various observational quantities for an MW mass halo for the different models, including the projected Sunyaev-Zeldovich (SZ) effect, soft X-ray emission (0.5--2 keV), dispersion measure, and column densities of oxygen ions (OVI, OVII, and OVIII) observable in absorption.

astro-ph.GA↗

arXiv2024

Impact of Property Covariance on Cluster Weak lensing Scaling Relations

We present an investigation into a hitherto unexplored systematic that affects the accuracy of galaxy cluster mass estimates with weak gravitational lensing. Specifically, we study the covariance between the weak lensing signal, $ΔΣ$, and the "true" cluster galaxy number count, $N_{\rm gal}$, as measured within a spherical volume that is void of projection effects. By quantifying the impact of this covariance on mass calibration, this work reveals a significant source of systematic uncertainty. Using the MDPL2 simulation with galaxies traced by the SAGE semi-analytic model, we measure the intrinsic property covariance between these observables within the 3D vicinity of the cluster, spanning a range of dynamical mass and redshift values relevant for optical cluster surveys. Our results reveal a negative covariance at small radial scales ($R \lesssim R_{\rm 200c}$) and a null covariance at large scales ($R \gtrsim R_{\rm 200c}$) across most mass and redshift bins. We also find that this covariance results in a $2-3\%$ bias in the halo mass estimates in most bins. Furthermore, by modeling $N_{\rm gal}$ and $ΔΣ$ as multi-(log)-linear equations of secondary halo properties, we provide a quantitative explanation for the physical origin of the negative covariance at small scales. Specifically, we demonstrate that the $N_{\rm gal}$-$ΔΣ$ covariance can be explained by the secondary properties of halos that probe their formation history. We attribute the difference between our results and the positive bias seen in other works with (mock)-cluster finders to projection effects. These findings highlight the importance of accounting for the covariance between observables in cluster mass estimation, which is crucial for obtaining accurate constraints on cosmological parameters.

astro-ph.CO↗

arXiv2024

Zooming by in the CARPoolGP lane: new CAMELS-TNG simulations of zoomed-in massive halos

Galaxy formation models within cosmological hydrodynamical simulations contain numerous parameters with non-trivial influences over the resulting properties of simulated cosmic structures and galaxy populations. It is computationally challenging to sample these high dimensional parameter spaces with simulations, particularly for halos in the high-mass end of the mass function. In this work, we develop a novel sampling and reduced variance regression method, CARPoolGP, which leverages built-in correlations between samples in different locations of high dimensional parameter spaces to provide an efficient way to explore parameter space and generate low variance emulations of summary statistics. We use this method to extend the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) to include a set of 768 zoom-in simulations of halos in the mass range of $10^{13} - 10^{14.5} M_\odot\,h^{-1}$ that span a 28-dimensional parameter space in the IllustrisTNG model. With these simulations and the CARPoolGP emulation method, we explore parameter trends in the Compton $Y-M$, black hole mass-halo mass, and metallicity-mass relations, as well as thermodynamic profiles and quenched fractions of satellite galaxies. We use these emulations to provide a physical picture of the complex interplay between supernova and active galactic nuclei feedback. We then use emulations of the $Y-M$ relation of massive halos to perform Fisher forecasts on astrophysical parameters for future Sunyaev-Zeldovich observations and find a significant improvement in forecasted constraints. We publicly release both the simulation suite and CARPoolGP software package.

astro-ph.GA↗

arXiv2023

Mapping the Intracluster Medium in the Era of High-resolution X-ray Spectroscopy

High-resolution spectroscopy in soft X-rays will open a new window to map multiphase gas in galaxy clusters and probe physics of the intracluster medium (ICM), including chemical enrichment histories, circulation of matter and energy during large-scale structure evolution, stellar and black hole feedback, halo virialization, and gas mixing processes. An eV-level spectral resolution, large field-of-view, and effective area are essential to separate cluster emissions from the Galactic foreground and efficiently map the cluster outskirts. Several mission concepts that meet these criteria have been proposed recently, e.g., LEM, HUBS, and SuperDIOS. This theoretical study explores what information on ICM physics could be recovered with such missions and the associated challenges. We emphasize the need for a comprehensive comparison between simulations and observations to interpret the high-resolution spectroscopic observations correctly. Using Line Emission Mapper (LEM) characteristics as an example, we demonstrate that it enables the use of soft X-ray emission lines (e.g., O VII/VIII and Fe-L complex) from the cluster outskirts to measure the thermodynamic, chemical, and kinematic properties of the gas up to $r_{200}$ and beyond. By generating mock observations with full backgrounds, analysing their images/spectra with observational approaches, and comparing the recovered characteristics with true ones from simulations, we develop six key science drivers for future missions, including the exploration of multiphase gas in galaxy clusters (e.g., temperature fluctuations, phase-space distributions), metallicity, ICM gas bulk motions and turbulence power spectra, ICM-cosmic filament interactions, and advances for cluster cosmology.

astro-ph.HE↗

arXiv2023

X-ray Absorption Lines in the Warm-Hot Intergalactic Medium: Probing Chandra observations with the CAMEL simulations

Known as the "Missing Baryon Problem", about one-third of baryons in the local universe remain unaccounted for. The missing baryons are thought to reside in the warm-hot intergalactic medium (WHIM) of the cosmic web filaments, which are challenging to detect. Recent Chandra X-ray observations used a novel stacking analysis and detected an OVII absorption line toward the sightline of a luminous quasar, hinting that the missing baryons may reside in the WHIM. To explore how the properties of the OVII absorption line depend on feedback physics, we compare the observational results with predictions obtained from the Cosmology and Astrophysics with MachinE Learning (CAMEL) Simulation suite. CAMELS consists of cosmological simulations with state-of-the-art supernova (SN) and active galactic nuclei (AGN) feedback models from the IllustrisTNG and SIMBA simulations, with varying strengths. We find that the simulated OVII column densities are higher in the outskirts of galaxies than in the large-scale WHIM, but they are consistently lower than those obtained in the Chandra observations, for all feedback runs. We establish that the OVII distribution is primarily sensitive to changes in the SN feedback prescription, whereas changes in the AGN feedback prescription have minimal impact. We also find significant differences in the OVII column densities between the IllustrisTNG and SIMBA runs. We conclude that the tension between the observed and simulated OVII column densities cannot be explained by the wide range of feedback models implemented in CAMELS.

astro-ph.CO↗

arXiv2022

The X-ray Angular Power Spectrum of Extended Sources in the eROSITA Final Equatorial Depth Survey

The eROSITA Final Equatorial Depth Survey (eFEDS), with a sky area of 140 square degrees with depth equivalent to the equatorial patch of the final eROSITA all-sky survey, represents the largest continuous non-full-sky X-ray fields to-date, making it the premier data set for measuring the angular power spectrum. In this work, we measure the X-ray angular power spectrum of galaxy clusters and groups in the eFEDS field. We show that the measured power spectrum is consistent with past observations, including the ROSAT All Sky Survey, and the Chandra COSMOS and Bootes fields. The predictions of cluster gas halo model that is calibrated from Chandra observations is also consistent with the eFEDS power spectrum. While the eFEDS does not have large enough sky coverage to provide meaningful cosmological constraints, we predict that the X-ray power spectrum from the cycle 4 of the eROSITA All-Sky Survey (eRASS4) will provide constraints on $Ω_M$ and $σ_8$ at the 10% level.

astro-ph.CO↗

arXiv2022

Triaxiality in galaxy clusters: Mass versus Potential reconstructions

Accounting for the triaxial shapes of galaxy clusters will become important in the context of upcoming cosmological surveys. We show that, compared to the gas density distribution, the cluster gravitational potential can be better characterised by a simple 3D model and is more robust against fluctuations. Perturbations in the gas density distribution can have a substantial influence on the derived thermodynamic properties, while cluster potentials are smooth and well-approximated by a spheroidal model. We use a statistical sample of 85 galaxy clusters from a large cosmological hydrodynamical simulation to investigate cluster shapes as a function of radius. In particular, we examine the shape of isodensity and isopotential shells and analyze how it is affected by the choice of component (gas vs. potential), substructure removal (for the gas density) and the definition of the computation domain (interior vs. shells). We find that the orientation and axis ratios of gas isodensity contours are degenerate with the presence of substructures and unstable against fluctuations. We observe that, as the derived cluster shape depends on the method used for removing the substructures, thermodynamic properties extracted from e.g. X-ray emissivity profiles suffer from this additional, often underestimated bias. In contrast, the shape reconstruction of the potential is largely unaffected by these factors and converges towards simple geometric models for both relaxed and dynamically active clusters. The observation that cluster potentials are better represented by simple geometrical models and reconstructed with a low level of systematics for both dynamically active and relaxed clusters suggests that by characterising galaxy clusters by their potential rather than by their mass, dynamically active and relaxed clusters could be combined in cosmological studies, improving statistics and lowering scatter.

astro-ph.CO↗

arXiv2022

The CAMELS project: public data release

The Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) project was developed to combine cosmology with astrophysics through thousands of cosmological hydrodynamic simulations and machine learning. CAMELS contains 4,233 cosmological simulations, 2,049 N-body and 2,184 state-of-the-art hydrodynamic simulations that sample a vast volume in parameter space. In this paper we present the CAMELS public data release, describing the characteristics of the CAMELS simulations and a variety of data products generated from them, including halo, subhalo, galaxy, and void catalogues, power spectra, bispectra, Lyman-$α$ spectra, probability distribution functions, halo radial profiles, and X-rays photon lists. We also release over one thousand catalogues that contain billions of galaxies from CAMELS-SAM: a large collection of N-body simulations that have been combined with the Santa Cruz Semi-Analytic Model. We release all the data, comprising more than 350 terabytes and containing 143,922 snapshots, millions of halos, galaxies and summary statistics. We provide further technical details on how to access, download, read, and process the data at \url{https://camels.readthedocs.io}.

astro-ph.CO↗

arXiv2021

Shock and Splash: Gas and Dark Matter Halo Boundaries around LambdaCDM Galaxy Clusters

Recent advances in simulations and observations of galaxy clusters suggest that there exists a physical outer boundary of massive cluster-size dark matter haloes. In this work, we investigate the locations of the outer boundaries of dark matter and gas around cluster-size dark matter haloes, by analyzing a sample of 65 massive dark matter halos extracted from the Omega500 zoom-in hydrodynamical cosmological simulations. We show that the location of accretion shock is offset from that of the dark matter splashback radius, contrary to the prediction of the self-similar models. The accretion shock radius is larger than all definitions of the splashback radius in the literature by 20-100%. The accretion shock radius defined using the steepest drop in the entropy pressure profiles is approximately 2 times larger than the splashback radius defined by the steepest slope in the dark matter density profile, and it is ~1.2 times larger than the edge of the dark matter phase-space structure. We discuss implications of our results for multi-wavelength studies of galaxy clusters.

astro-ph.CO↗