arXiv subjects

A. Liu

Publications and source records attributed to A. Liu.

At least 19 recordsLinked to original sources

arXiv2026

The SRG/eROSITA All-Sky Survey: Early dark energy and Hubble constant from the cluster mass function

The evolution of the mass function of massive galaxy clusters is a well-established probe of cosmology. Using the eROSITA X-ray instrument on board the Spectrum Roentgen Gamma (SRG) mission, the western Galactic hemisphere of eROSITA's first All-Sky Survey (eRASS1) delivers a uniformly selected and securely confirmed sample of 5259 galaxy clusters spanning $0.1 < z < 0.8$. When combined with overlapping weak lensing data from DES Year 3, KiDS, and HSC for mass calibration, this dataset enables precise tests of the standard $\Lambda$CDM framework and beyond. In this work, we use the $0.1 < z < 0.45$ subsample of the eRASS1 cluster catalog to place constraints on an axion-like Early Dark Energy (EDE) scenario. Such models have been proposed as a possible mechanism to alleviate the tension between early- and late-Universe measurements of the Hubble constant. In this framework, a scalar field temporarily enhances the cosmic expansion rate around the epoch of recombination before rapidly diluting at later times, leaving distinct imprints on structure growth. We leverage these signatures to present the first constraints on EDE derived from galaxy cluster number counts. Using eRASS1 number counts alone, we obtain an upper limit on the maximum EDE fraction of $f_{\rm EDE} < 0.3$, consistent with primary CMB analyses. Combining our cluster analysis with primary CMB measurements, baryon acoustic oscillations, and CMB lensing, while notably excluding distance-ladder calibration data, yields results consistent with a nonzero EDE contribution and $H_0$ values compatible with late-Universe measurements. The most significant detection, at $\sim 3.2\sigma$, arises from the joint analysis of the eRASS1 sample with the full set of external datasets, yielding $f_{\rm EDE} = 0.10^{+0.04}_{-0.03}$ and $H_0 = 71.4 \pm 1.4$ km/s/Mpc. [ABRIDGED]

astro-ph.CO↗

arXiv2026

The SRG/eROSITA All-Sky Survey DR2: Cumulative X-ray catalogues from the first three surveys and multi-wavelength counterparts in the western Galactic hemisphere

The eROSITA telescope array on board the Spektrum-Roentgen-Gamma (SRG) mission began its all-sky survey program in December 2019, scanning the sky at an approximately six-month cadence. Here, we present new catalogues of point-like and extended X-ray sources derived from the first three completed eROSITA all-sky surveys (eRASS:3), covering the western Galactic hemisphere, which Germany's eROSITA consortium holds proprietary rights for. We describe the observational strategy, data processing, and analysis pipelines. We also characterise the resulting X-ray source populations. The eRASS:3 main catalogue contains nearly two million sources, including 1,911,744 point-like and 63,796 extended sources, detected in the 0.2-2.3 keV energy band, eROSITA's most sensitive energy window. This volume has doubled the X-ray source content of eRASS1 and provides a comprehensive census of X-ray-emitting objects across diverse astrophysical classes. We also released a secondary hard catalogue of nearly 15,000 sources detected in the harder 2.3-5.0 keV energy band. In addition, we released six catalogues, three for the main sample and three for the hard sample, in which we identify and classify the optical and infrared counterparts of eRASS:3 point-like sources. This approach delivers a homogeneous, high-quality identification of mostly extragalactic X-ray emitters; for example, we estimate that approximately 88% of the 1.4 million counterparts identified within the footprints of the Legacy Survey Imaging for DESI are extragalactic sources. This work has enabled the generation of samples optimised for completeness and purity, while expanding the discovery space for rare populations. The second data release (DR2) of the SRG/eROSITA all-sky survey is a catalogue-only release, comprising the catalogues presented in this work together with an updated version of the eROSITA upper flux limit server.

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arXiv2026

The three-dimensional shapes of the galaxy cluster intracluster medium in eRASS1

The three-dimensional shapes of clusters are important for understanding the astrophysics of the clusters and as a probe in cosmological studies. We estimate the most probable three-dimensional shape of galaxy clusters in the first eROSITA All-sky survey eRASS1 using stereology. Our sample is the largest well-defined sample of clusters, and the most probable shape estimated using our method can be used as a prior for cluster shape models in cosmological, cluster, and weak lensing studies. The first all-sky survey with SRG/ eROSITA resulted in a sample of approximately 12,000 optically confirmed galaxy groups and clusters. We used a well-defined subsample of 3254 clusters from the eRASS1 survey and estimated the most probable shape of the clusters by constraining the probability density function (PDF) of the ellipticity of the clusters. We simulated the projected appearance of clusters with a distribution of three-dimensional shapes (prolate and oblate) and obtained the distribution of their ellipticity. This distribution was then compared with the measured distribution of ellipticities from the eRASS1 cluster sample to infer the three-dimensional shapes consistent with the data. We used Monte Carlo methods to estimate the most probable axial ratios l, w, where l $\equiv$ L/T ,w $\equiv$ W/T , and L, W, T are major, intermediate, and minor axes of the cluster. We did not require any additional probe (optical, SZ, etc.) to constrain the probable shape of the clusters. We describe the ellipticity PDF of the eRASS1 clusters with a normal distribution mean ($\mu$) = 0.79 and a standard deviation ($\sigma$) = 0.25. The most probable shape of the clusters in our eRASS1 subsample is estimated to be (l, w) = (1.51 $\pm$ 0.27, 1.17 $\pm$ 0.27), with prolate shapes being preferred over oblate shapes.

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arXiv2026

The X-ray properties and structure of A3571 up to $R_{500}$

Abell 3571 is a nearby, X-ray bright galaxy cluster located in the Shapley Supercluster. Although it appears morphologically relaxed in X-ray images, multiwavelength observations reveal subtle indications of residual dynamical activity, likely associated with past merger events. Using wide-field ($1^{\circ} \times 1^{\circ}$) data from the Einstein Probe Follow-up X-ray Telescope (EP-FXT), we extend measurements of the cluster's properties beyond its $R_{500}$ radius. We detect surface-brightness excesses on both the northern and southern sides, consistent with previous XMM-Newton results. The temperature, pressure, and entropy in the northern excess region are lower than the average values, whereas those on the southern side are slightly higher. However, we find no evidence for cold fronts or shocks. These features can be interpreted as sloshing motions triggered by an off-center minor merger. Our findings suggest that, despite its symmetric appearance, A3571 is still recovering from a minor merger and is currently in a post-merger phase. This work also demonstrates the excellent capability of EP-FXT for probing the outskirts of galaxy clusters.

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arXiv2026

The SRG/eROSITA all-sky survey: The morphologies of clusters of galaxies: II. The intrinsic distributions of morphological parameters

X-ray selected surveys of clusters of galaxies have been reported to contain more regular cool core clusters compared to samples selected using the Sunyaev-Zel'dovich (SZ) effect. Morphology population studies on X-ray selected clusters will be biased without taking into account selection, as cool cores are more easily detected at low redshifts, but can be mistaken for point sources at high redshift. eROSITA, aboard SRG, found over 12000 optically-identified clusters in its first survey, eRASS1. Taking account of the selection function obtained from simulations, we obtain using a Bayesian framework the intrinsic distribution of morphological parameters, including the concentration, central density, cuspiness, ellipticity and slosh. We construct scaling relations for the parameters as a function of redshift (z) and luminosity (LX), and study their distribution within z or LX bins. We find that the concentration in a scaled aperture evolves positively with LX, similarly to the central scaled density, and negatively with z. When using a fixed aperture, its evolution with LX is lower, but also dependent on the choice of cluster centre. The mean ellipticity does not significantly evolve with z or LX. eRASS1 clusters show indications of higher concentrations compared to SZ-selected objects, even after taking account the selection; this suggests that if our X-ray selection model is correct SZ-selected clusters may also suffer from morphological selection effects. We compare different parameter distribution models in bins of z and LX. The distribution of concentration and ellipticity is generally consistent with a normal one, but other parameters such as the central density and cuspiness strongly favour more complex distributions. However, modelling of all clusters as a single population generally prefers non-normal distributions. [abridged]

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arXiv2025

The eROSITA Final Equatorial-Depth Survey (eFEDS): X-ray stacking analysis of Subaru's optically selected clusters spanning low richness regime

This is the second paper in a series exploring the X-ray properties of galaxy clusters optically selected by the Subaru Hyper Suprime-Cam (HSC) survey, using data from the SRG/eROSITA Final Equatorial-Depth Survey (eFEDS). We aim to investigate scaling relations between observable cluster properties and mass, and to study the radial X-ray profiles of a large sample of optically selected clusters. We analyze a sample of 997 CAMIRA clusters with richness $N > 15$ and redshifts of $0.1 < z < 1.3$. Using bolometric luminosities derived from count rates and a weak-lensing mass calibration, we study the $L-M$ and $N-M$ scaling relations through stacking analysis, while accounting for selection effects and redshift evolution. We also compare clusters with and without X-ray counterparts in the eFEDS catalog in terms of their scaling relations and surface brightness profiles. The best-fit $L-M$ slope ($1.56^{+0.14}_{-0.12}$) is slightly steeper than the self-similar prediction, yet remains consistent with our previous findings. The $N-M$ slope ($0.766^{+0.070}_{-0.060}$) broadly agrees with theoretical expectations and other optical samples. The data do not require any additional redshift evolution beyond the standard self-similar scaling, although current constraints on evolution remain weak. X-ray detected clusters exhibit a marginally steeper $L-M$ slope, higher central surface brightness, and more centrally concentrated X-ray profiles than undetected systems. Our results highlight systematic differences in the X-ray properties between optically and X-ray selected cluster samples. This study extends scaling relation analyses into lower mass and luminosity regimes, demonstrating the value of combining deep X-ray and optical surveys like eROSITA and Subaru HSC.

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arXiv2025

From Observations to Simulations: A Neural-Network Approach to Intracluster Medium Kinematics

We present a systematic comparison between {\it XMM-Newton} velocity maps of the Virgo, Centaurus, Ophiuchus and A3266 clusters and synthetic velocity maps generated from the Illustris TNG-300 simulations. Our goal is to constrain the physical conditions and dynamical states of the intracluster medium (ICM) through a data-driven approach. We employ a Siamese Convolutional Neural Network (CNN) designed to identify the most analogous simulated cluster to each observed system based on the morphology of their line-of-sight velocity maps. The model learns a high-dimensional similarity metric between observations and simulations, allowing us to capture subtle kinematic and structural patterns beyond traditional statistical tests. We find that the best-matching simulated halos reproduce the observed large-scale velocity gradients and local kinematic substructures, suggesting that the ICM motions in these clusters arise from a combination of gas sloshing, AGN feedback, and minor merger activity. Our results demonstrate that deep learning provides a powerful and objective framework for connecting X-ray observations to cosmological simulations, offering new insights into the dynamical evolution of galaxy clusters and the mechanisms driving turbulence and bulk flows in the hot ICM.

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arXiv2025

The SRG/eROSITA all-sky survey: X-ray scaling relations of galaxy groups and clusters in the western Galactic hemisphere

The soft X-ray telescope on board the Spectrum-Roentgen-Gamma (SRG) mission, eROSITA (extended ROentgen Survey with an Imaging Telescope Array), has produced the largest sample to date of galaxy groups and clusters detected via their intracluster/intragroup medium (ICM/IGrM) emission. Scaling relations between the intrinsic properties of these systems provide valuable insight into their formation and evolution. In this work, we investigate the scaling relations between key physical properties, such as soft band X-ray luminosity, temperature, gas mass, and the low-scatter mass proxy $Y_{\rm X}$, for the galaxy groups and clusters detected in the first eROSITA All-Sky Survey (eRASS1). Our analysis fully accounts for selection effects and the redshift evolution of the observable distributions. We construct a high-purity sample of $3061$ galaxy groups and clusters spanning the redshift range $0.05<z<1.07$ and mass range of $1.1\times10^{13}<M_{500}/$M$_{\odot}<1.6\times10^{15}$. This represents the largest sample to date used for scaling relation analysis. The selection function, derived from state-of-the-art simulations of the eROSITA sky, is rigorously incorporated into our modeling. We report best-fit parameters - normalization, slope, redshift evolution, and intrinsic scatter - for a set of scaling relations: $L_{\mathrm{X}}-T$, $L_{\mathrm{X}}-M_{\rm gas}$, $L_{\mathrm{X}}-Y_{\rm X}$, as well as the $M_{\rm gas}-T$ relation. Our best-fit models indicate that the slopes of the scaling relations deviate significantly from self-similar expectations, while the redshift evolution remains consistent with the self-similar model. The fits exhibit small statistical uncertainties, likely owing to the large sample size. Our results are in good agreement with previous observational studies that account for selection effects, as well as with simulations that incorporate non-gravitational physics.

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arXiv2025

The Quiescent Merging Nature of the Coma Cluster Revealed by ICM Velocity Structure

The hot gas permeating galaxy clusters-the intracluster medium (ICM)-is a key tracer of their assembly history and internal dynamics. Understanding the motion of this gas provides critical insight into processes such as mergers, turbulence, and energy dissipation in the largest gravitationally bound structures in the Universe. The Coma cluster is a nearby, massive system long suspected to be dynamically disturbed. Previous high-resolution X-ray spectroscopy with the XRISM mission revealed bulk motions in the cluster core and southern regions. Here we present new XRISM Resolve observations of a northern region in Coma, which reveal a coherent velocity gradient of nearly $530 km/s across the cluster from south to north. We find that the hot gas in this northern region exhibits modest line-of-sight motions and uniform thermodynamic properties, indicating relatively mild local disturbances. The consistent levels of turbulence throughout the cluster suggest that the energy from a past merger has been distributed on large scales. These findings provide compelling evidence for an off-axis merger event and demonstrate how high-resolution X-ray spectroscopy can uncover subtle dynamical signatures in the ICM, offering important constraints for simulations of cluster evolution.

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arXiv2025

The SRG/eROSITA All-Sky Survey. Detection of shock-heated gas beyond the halo boundary into the accretion region

The hot gas in the outskirts of galaxy cluster-sized halos, extending around and beyond the virial radius into nearby accretion regions, remains among one of the least explored baryon components of the large-scale cosmic structure. We present a stacking analysis of 680 galaxy clusters located in the western Galactic hemisphere, using data from the first two years of the SRG/eROSITA All-Sky Survey. The stacked X-ray surface brightness (SB) profile reveals a statistically significant signal extending out to 2 r_200m (~4.5 Mpc). The best-fit SB profile is well described by a combination of terms describing orbiting and infalling gas, with a transition occurring around r_200m. At this radius, the gas number density corresponds to a baryon overdensity of about 30. By integrating the density profile out to r_200m, we inferred a gas fraction exceeding the universal baryon fraction, assuming a typical halo concentration. However, correcting for possible clumping effects reduces the baryon fraction by more than 20%. Additionally, we examined the distribution of hot gas in massive clusters in the IllustrisTNG simulations, from the halo center to the accretion region. This analysis reveals differences in radial gas profiles depending on whether the direction points toward voids or toward nearby cosmic filaments. Beyond r_200m, the density profile along the filament direction exceeds that along the void direction. This pattern aligns with the observed transition radius between the one-halo and two-halo terms, suggesting that r_200m is the approximate radius marking the location at which cosmic filaments connect to galaxy clusters. Meanwhile, comparisons of the gas density and gas fraction profiles between the observation and the IllustrisTNG simulation suggest that the feedback processes in the stacking sample are more efficient at distributing gas to large radii than the IllustrisTNG model.

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arXiv2025

The SRG/eROSITA All-Sky Survey $J$-Band Follow-Up Observations for Selected High-Redshift Galaxy Cluster Candidates

We select galaxy cluster candidates from the high-redshift (BEST_Z > 0.9) end of the first SRG/eROSITA All-Sky Survey (eRASS1) galaxy cluster catalogue, for which we obtain moderately deep J-band imaging data with the OMEGA2000 camera at the 3.5m telescope of the Calar Alto Observatory. We include J-band data of four additional targets obtained with the three-channel camera at the 2m Fraunhofer telescope at the Wendelstein Observatory. We complement the new J-band photometric catalogue with forced photometry in the i- and z-bands of the tenth data release of the Legacy Survey (LSDR10) to derive the radial colour distribution around the eRASS1 clusters. Without assuming a priori to find a cluster red sequence at a specific colour, we try to find a radially weighted colour over-density to confirm the presence of high-redshift optical counterparts for the X-ray emission. We compare our confirmation with optical properties derived in earlier works based on LSDR10 data to refine the existing high-redshift cluster confirmation of eROSITA-selected clusters. We attempt to calibrate the colour-redshift-relation including the new J-band data by comparing our obtained photometric redshift estimate with the spectroscopic redshift of a confirmed, optically selected, high-redshift galaxy cluster. We confirm 9 out of 18 of the selected galaxy cluster candidates with a radial over-density of similar coloured galaxies for which we provide a photometric redshift estimate. We can report an increase in the relative colour measurement precision from 8% to 4% when including J-band data. In conclusion, our findings indicate a not insignificant spurious contaminant fraction at the high-redshift end (BEST_Z > 0.9) of the eROSITA/eRASS1 galaxy cluster catalogue, as well as it underlines the necessity for wide and deep near infrared imaging data for confirmation and characterisation of high-$z$ galaxy clusters.

astro-ph.CO↗

arXiv2025

Imaging-spectroscopy diagnosis of the giant sloshing spiral in the Virgo cluster with the Einstein Probe Follow-up X-ray Telescope

We performed deep X-ray observations of the Virgo cluster using the Einstein Probe Follow-up X-ray Telescope (EP-FXT) with a total exposure of 295 ks. Leveraging the large field of view (FoV) and low particle background of EP-FXT, the image reveals a giant spiral feature connecting the cold fronts in the northwest and southeast, forming a coherent structure consistent with earlier results from XMM-Newton and Suzaku. We also present two-dimensional maps of temperature, metallicity, and entropy across the Virgo Cluster, covering a FoV of approximately 28.5 arcmin. These maps clearly show a spiral structure with high density, low temperature, high metallicity, and low entropy. The results support a scenario where the spiral morphology arises from gas sloshing driven by a minor merger. Additionally, EP-FXT temperature measurements agree well with XMM-Newton data within uncertainties.

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arXiv2025

Chemical enrichment of ICM within the A3266 cluster I: radial profiles

We present a detailed study of the elemental abundances distribution of the intracluster medium (ICM) within the A3266 cluster using {\it XMM-Newton} observations. This analysis uses EPIC-pn data, including a new energy scale calibration, which allows us to measure velocities with uncertainties down to $\Delta v \sim 80$ km/s, and MOS observations. We measured radial O, Mg, Si, S, Ar, Ca, and Fe profiles. This is the first study of elemental abundances beyond Fe using X-ray observations within the A3266 cluster. The abundance profiles display discontinuities similar to those obtained for the temperature. We modeled the X/Fe ratio profiles with a linear combination of type~Ia supernovae (SNIa) and core-collapse supernovae (SNcc) models. We found that the SNIa ratio over the total cluster enrichment tends to be uniform, with a $42\pm 5\%$ contribution. Such a trend supports an early ICM enrichment scenario, with most metals produced before clustering.

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arXiv2025

eROSITA clusters dynamical state and their impact on the BCG luminosity

The Spectrum Roentgen Gamma/eROSITA first public release contains 12,247 clusters and groups. We use the offset between the Brightest Cluster Galaxy (BCG) and the X--ray peak (D$_{\rm BCG-X}$) to classify the cluster dynamical state of 3,946 galaxy clusters and groups. The X--ray peaks come from the eROSITA survey while the BCG positions come from the DECaLS DR10 optical data, which includes the DECam eROSITA Survey optical data. We aim to investigate the evolution of the merger and relaxed cluster distributions with redshift and mass, and their impact on the BCG. We model the distribution of D$_{\rm BCG-X}$ as the sum of two Rayleigh distributions representing the cluster's relaxed and disturbed populations, and explore their evolution with redshift and mass. To explore the impact of the cluster's dynamical state on the BCG luminosity, we separate the main sample according to the dynamical state. We define clusters as relaxed if D$_{\rm BCG-X}$ < 0.25$r_{500}$, disturbed if D$_{\rm BCG-X}$>0.5$r_{500}$, and as `diverse' otherwise. We find no evolution of the merging fraction in redshift and mass. We observe that the width of the relaxed distribution to increase with redshift, while the width of the two Rayleigh distributions decreases with mass. The analysis reveals that BCGs in relaxed clusters are brighter than BCGs in both the disturbed and diverse cluster population. The most significant differences are found for high mass clusters at higher redshift. The results suggest that BCGs in low-mass clusters are less centrally bound than those in high-mass systems, irrespective of dynamical state. Over time, BCGs in relaxed clusters progressively align with the potential center. This alignment correlates with their luminosity growth relative to BCGs in dynamically disturbed clusters, underscoring the critical role of the clusters dynamical state in regulating BCG evolution. [Abridged]

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arXiv2025

The SRG/eROSITA all-sky survey: View of the Fornax galaxy cluster

The Fornax cluster is one of the closest X-ray-bright galaxy clusters. Previous observations of the intracluster medium were limited to less than R500. We aim to significantly extend the X-ray coverage. We used data from 5 SRG/eROSITA all-sky surveys and performed a detailed 1- and 2-dimensional X-ray surface brightness analysis, tracing hot gas emission from kpc to Mpc scales with a single instrument. We compared the results to those from a recent numerical simulation of the local Universe (SLOW) and correlated the X-ray emission distribution with that of other tracers, including cluster member galaxies, ultra-compact dwarf galaxies, intracluster globular clusters, and HI-tail galaxies. We detect X-ray emission beyond the virial radius, R100=2.2 deg. In the inner regions within R500, we see previously known features, such as a large-scale spiral-shaped edge; however, we do not find obvious evidence of the bow shock several hundred kpc south of the cluster center predicted by previous numerical simulations of the Fornax cluster. Instead, we discover emission fingers beyond R500 to the west and southeast and excesses that stretch out far beyond the virial radius. They might be due to gas being pushed outward by the previous merger with NGC 1404 or due to warm-hot gas infall along large-scale filaments. Intriguingly, we find the distributions of the other tracers - galaxies and globular clusters - to be correlated with the X-ray-excess regions, favoring the infall scenario. Interestingly, we also discover an apparent bridge of low-surface-brightness emission beyond the virial radius connecting to the Fornax A galaxy group, which is also traced by the member galaxy and globular cluster distribution. The gas distribution in the SLOW simulation shows similar features as those we have discovered with eROSITA. With eROSITA, we witness the growth of a cluster along large-scale filaments.

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arXiv2025

Discovery of large-scale radio emission enveloping the mini-halo in the most X-ray luminous galaxy cluster RX~J1347.5-1145

Diffuse radio sources, known as mini-halos and halos, are detected at the centres of galaxy clusters. These centralized diffuse sources are typically observed individually, with both appearing together only in rare cases. The origin of the diffuse radio sources in such systems remains unclear. We investigate the formation of large-scale radio emission in the most X-ray luminous, massive galaxy cluster RXJ~1347.5-1145 which is known to host a mini-halo at its centre and possibly additional more extended emission. We conduct deep multi-frequency observations of the galaxy cluster using the MeerKAT at 1.28 GHz and the uGMRT (upgraded Giant Metrewave Radio Telescope) at 1.26 GHz and 700 MHz. We characterize the brightness and spectral properties of the central diffuse sources and combine our radio observations with \textit{Chandra} X-ray data to explore the correlation between the cluster's non-thermal and thermal emissions. We confirm the presence of the diffuse emission and find that it extends up to 1~Mpc in size. Our multi-wavelength data reveal that the central diffuse emission consists of two distinct components: a mini-halo located in the cluster core and a larger radio halo extending around it. The correlation between radio and X-ray surface brightness in both sources indicates a strong connection between the non-thermal and thermal properties of the ICM. The differing slopes in the $I_R-I_X$ and $\alpha-I_X$ relations suggest that distinct mechanisms are responsible for the formation of the mini-halo and halo. The properties of the halo align with the turbulent model, while both turbulent and hadronic processes may contribute to the formation of the mini-halo.

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arXiv2025

The SRG/eROSITA all-sky survey: Constraints on Ultra-light Axion Dark Matter through Galaxy Cluster Number Counts

Ultralight axions are hypothetical scalar particles that influence the evolution of large-scale structures of the Universe. Depending on their mass, they can potentially be part of the dark matter component of the Universe as candidates commonly referred to as fuzzy dark matter. While strong constraints have been established for pure fuzzy dark matter models, the more general scenario where ultralight axions constitute only a fraction of the dark matter has been limited to only a few observational probes. In this work, we use the galaxy cluster number counts obtained from the first All-Sky Survey (eRASS1) of the SRG/eROSITA mission together with gravitational weak lensing data from the Dark Energy Survey, the Kilo-Degree Survey, and the Hyper Suprime-Cam to constrain the fraction of ultralight axions in the mass range $10^{-32}$ eV to $10^{-24}$ eV. We put upper bounds on the ultralight axion relic density $\Omega_\mathrm{a}$ in independent logarithmic axion mass bins by performing a full cosmological parameter inference. We find an exclusion region in the intermediate ultralight axion mass regime with the tightest bounds reported so far in the mass bins around $m_\text{a} = 10^{-27}$ eV with $\Omega_\text{a} < 0.0035$ and $m_\text{a} = 10^{-26}$ eV with $\Omega_\text{a} < 0.0079$ (95% C.L.). When combined with cosmic microwave background probes, these bounds are tightened to $\Omega_\text{a} < 0.0030$ in the $m_\text{a} = 10^{-27}$ eV mass bin and $\Omega_\text{a} < 0.0058$ in the $m_\mathrm{a} = 10^{-26}$ eV mass bin (95% C.L.). This is the first time that constraints on ultralight axions have been obtained using the growth of structure measured by galaxy cluster number counts. These results pave the way for large surveys, which can be utilized to obtain tight constraints on the mass and relic density of ultralight axions with better theoretical modeling of the abundance of halos.

astro-ph.CO↗

arXiv2025

The SRG/eROSITA all-sky survey: The morphologies of clusters of galaxies I: A catalogue of morphological parameters

The first SRG/eROSITA all-sky X-ray survey, eRASS1, resulted in a catalogue of over twelve thousand optically-confirmed galaxy groups and clusters in the western Galactic hemisphere. Using the eROSITA images of these objects, we measure and study their morphological properties, including their concentration, central density and slope, ellipticity, power ratios, photon asymmetry, centroid shift and Gini coefficient. We also introduce new forward-modelled parameters which take account of the instrument point spread function (PSF), which are slosh, which measures how asymmetric the surface brightness distribution is, and multipole magnitudes, which are analogues to power ratios. Using simulations, we find some non forward-modelled parameters are strongly biased due to PSF and data quality. For the same clusters, we find similar values of concentration and central density compared to results by ourselves using Chandra and previous results from XMM-Newton. The population as a whole has log concentrations which are typically around 0.3 dex larger than South Pole Telescope or Planck-selected samples and the deeper eFEDS sample. The exposure time, detection likelihood threshold, extension likelihood threshold and number of counts affect the concentration distribution, but generally not enough to reduce the concentration to match the other samples. The concentration of clusters in the survey strongly affects whether they are detected as a function of redshift and luminosity. We introduce a combined disturbance score based on a Gaussian mixture model fit to several of the parameters. For brighter clusters, around 1/4 of objects are classified as disturbed using this score, which may be due to our sensitivity to concentrated objects.

astro-ph.CO↗