Galaxy Clusters Research Articles

Position of X-ray low surface brightness clusters in the cosmic filament network

The aim of this work is to study the position of gas-rich and gas-poor galaxy clusters within the large-scale structure and, in particular, their distance to filaments. Our sample is built from 29 of the 34 clusters in the X-ray unbiased cluster sample (XUCS), a velocity-dispersion-selected sample for which various properties, including masses, gas fractions, and X-ray surface brightness, are available in the literature. We computed the projected distance between each cluster and the spine of the nearest filament with the same redshift, and we investigated the link between this distance and the previously mentioned properties of the clusters, in particular their gas content. The average distance between clusters and filaments is larger for low X-ray surface brightness clusters than for those of high surface brightness, with intermediate brightness clusters being an intermediate case. The minimum distance follows a similar trend, with rare cases of low surface brightness clusters found at distances smaller than 2 Mpc from the spine of filaments. However, the Kolmogorov-Smirnov statistical test is not able to exclude the null hypothesis that the two distributions come from the same parent one. We speculate that the position of galaxy clusters within the cosmic web could have a direct impact on their gas mass fraction and hence on their X-ray surface brightness since the presence of a filament can hinder the outward flow of gas induced by the central active galactic nucleus (AGN) and reduce the time required for this gas to fall inward after the AGN is shut. However, a larger sample of clusters is needed in order to derive a statistically robust conclusion.

MeerKAT discovery of gigahertz radio emission extending from Abell 3017 towards Abell 3016

Cosmic filaments are vast, faint structures that connect galaxy clusters, often challenging to detect directly. However, filaments between pre-merger cluster pairs become more visible due to gas heating and compression while the clusters are approaching, enabling detection in X-ray and radio wavelengths. The clusters Abell 3017 and Abell 3016 are located within such a large-scale filament. A prominent X-ray bridge has been detected connecting the two clusters and a potential galaxy group between them. The aim of this work is to investigate the existence of a radio bridge in the filament between Abell 3017 and Abell 3016, to explore other diffuse radio structures within this system, and to investigate the origins of these diffuse radio emission. We analysed MeerKAT L-band data to study the morphology and spectra of the diffuse radio structures in Abell 3016-Abell 3017. X-ray imaging and spectral analysis were carried out with archival and data. Additionally, correlations between radio (I_R) and X-ray surface brightness (I_X) were generated to explore the connections between thermal and non-thermal components in the diffuse radio emission. We detected a faint radio bridge with an average surface brightness of ∼ 0.1 μ Jy at 1280 MHz using MeerKAT. It connects Abell 3017 with a potential galaxy group and extends towards Abell 3016, aligning with the X-ray bridge. A high X-ray temperature of $7.09 ± 0.54$ keV detected in the bridge region suggests an interaction between Abell 3017 and the group. In Abell 3017, we identified two distinct components of diffuse radio emission: a radio mini-halo and an outer radio halo with a northern extension (N-extension hereafter). The radio surface brightness profile of Abell 3017 shows a steep inner component consistent with other mini-halos, and a faint outer component likely linked to an infalling subcluster. The I_ R -I_ X diagram indicates superlinear and sub-linear correlations for the mini-halo and N-extension, respectively. We proposed three plausible explanations for the origin of the radio bridge: (1) it is an inter-cluster radio bridge connecting the two clusters in a filament, enhanced by interactions with the embedded galaxy group; (2) it results from an interaction between Abell 3017 and the galaxy group after their primary apocentric passage, with the group currently falling back towards Abell 3017; (3) it is a cluster radio relic associated with a merger shock, appearing as a bridge due to its face-on orientation. In Abell 3017, the mini-halo is likely powered by gas sloshing, resulting from an offset merger that left the cluster's cool core intact. Turbulence from an infalling subcluster likely contributes to the formation of the outer radio halo.

Simulating realistic self-interacting dark matter models including small and large-angle scattering

Dark matter (DM) self-interactions alter matter distribution on galactic scales and alleviate tensions with observations. A feature of the self-interaction cross section is its angular dependence, which influences offsets between galaxies and DM halos in merging galaxy clusters. While algorithms for modelling mostly forward-dominated or mostly large-angle scatterings exist, incorporating realistic angular dependencies within N-body simulations remains challenging. To efficiently simulate models with a realistic angle dependence, such as light mediator models, we developed, validated, and applied a novel method. We combined existing approaches to describe small- and large-angle scattering regimes within a hybrid scheme. Below a critical angle, the scheme uses the effective description of small-angle scattering via a drag force combined with transverse momentum diffusion, while above the angle, it samples the dependence explicitly. We first verified the scheme using a test set-up with known analytical solutions, and we checked that our results are insensitive to the choice of the critical angle within an expected range. Next, we demonstrated that our scheme speeds up the computations by multiple orders of magnitude for realistic light mediator models. Finally, we applied the method to galaxy cluster mergers. We discuss the sensitivity of the offset between galaxies and DM to the angle dependence of the cross section. Our scheme ensures accurate offsets for mediator mass m_ϕ and DM mass m_χ within the range $0.1v/c m_ϕ/m_χ v/c$, while for larger (smaller) mass ratios, the offsets obtained for isotropic (forward-dominated) self-scattering are approached. Here, v is the typical velocity scale. Equivalently, the upper condition can be expressed as $1.1 tot /σ_ T 10$ for the ratio of the total and momentum transfer cross sections, with the ratio being $1$ (∞) in the isotropic (forward-dominated) limits.

Exploring the Formation, Dynamics, and Structure of Galaxy Clusters: A Comprehensive Analysis

This study explores the formation, structure, and dynamics of galaxy groups and clusters, highlighting their significance in the cosmic web. Galaxy clusters are massive, self-gravitating systems that display complex interactions influenced by dark matter and the intracluster medium (ICM). Recent advancements in X-ray and optical observations have significantly improved our understanding of the morphology and kinematics of these clusters, shedding light on the processes governing their evolution. The research employs the virial theorem to determine mass distributions and examines gravitational lensing effects to probe the mysterious nature of dark matter. Key challenges addressed include understanding how galaxy clusters form, analyzing the dynamics of the galaxies within them, and identifying the missing mass that holds these structures together. By combining observational data with theoretical models, this investigation aims to enhance our comprehension of the Universe's large-scale structure and the fundamental forces driving galaxy group dynamics.

Deep view of the intracluster light in the Coma cluster of galaxies

The detection and study of the intracluster light (ICL) in rich clusters of galaxies has been a longstanding challenge and key focus. Using the lowest-surface-brightness images of the Coma cluster of galaxies in the g and r bands, from the Halos and Environment of Nearby Galaxies (HERON) Coma Cluster Project we obtained the most extensive image of ICL in a single cluster to date, spreading over 1.5 Mpc from the cluster core. The unprecedented wealth of spectroscopic data from the Dark Energy Spectroscopic Instrument (DESI) Early Data Release, along with a compilation from the NASA/IPAC Extragalactic Database and available data from the literature enabled the identification of 2,157 galaxy members within Coma; on this basis, 42 distinct groups were identified. The synergy between these high-quality data allowed us to : 1) calculate ICL fractions of $19.9±0.5$% and $19.6±0.6$% in the g and r bands, respectively, consistent with a dynamically active cluster; 2) unveil Coma's faintest tidal features; and 3) provide a comprehensive picture of the dynamics and interactions within this complex system . Our findings indicate that the ICL connects several of these groups in a filamentous network, from which we can infer ongoing dynamical processes. In particular, we identified a faint stellar bridge linking the core of Coma with the galaxy NGC 4839, providing compelling evidence that this galaxy has already traversed the central region of the cluster.

A candidate quadruple AGN system at z∼3

Multiple galaxies hosting active galactic nuclei (AGNs) at kiloparsec separations from each other are exceedingly rare, and in fact, only one quadruple AGN is known so far. These extreme densities of AGNs are expected to pinpoint protocluster environments and therefore should be surrounded by large galaxy overdensities. In this letter, we present another quadruple AGN candidate at z ∼ 3 including two SDSS quasars at a separation of roughly 480 kpc. The brighter quasar is accompanied by two AGN candidates (a type 1 AGN and a likely type 2 quasar) at a close (∼ 20 kpc) separation identified through emission line ratios, line widths, and high ionization lines, such as The extended Lyα emission associated with the close triple system is more modest in extent and brightness compared to similar multiple AGN systems and could be caused by ram-pressure stripping of the type 2 quasar host during infall into the central dark matter halo. The predicted evolution of the system into a z=0 galaxy cluster with the AGN host galaxies forming the brightest cluster galaxy needs to be further tested by galaxy overdensity studies on large scales around the quadruple AGN candidate. If confirmed as a quadruple AGN with X-ray observations or rest-frame optical line ratios, this system would represent a second AGN quartet and be the highest-redshift multiplet and the closest high-redshift triplet known.

Corrigendum: The properties of magnetised cold filaments in a cool-core galaxy cluster

Corrigendum: The properties of magnetised cold filaments in a cool-core galaxy cluster

Monopole Fluctuations in Galaxy Surveys

Abstract Galaxy clustering provides a powerful way to probe cosmology. This requires understanding of the background mean density of galaxy samples, which is estimated from the survey itself by averaging the observed galaxy number density over the angular position. The angle average includes not only the background mean density but also the monopole fluctuation at each redshift. Here for the first time we compute the monopole fluctuations in galaxy surveys and investigate their impact on galaxy clustering. The monopole fluctuations vary as a function of redshift, and it is correlated with other fluctuations, affecting the two-point correlation function measurements. In an idealized all-sky survey, the rms fluctuation at z = 0.5 can be as large as 7% of the two-point correlation function in amplitude at the baryonic acoustic oscillation scale, and it becomes smaller than 1% at z > 2. The monopole fluctuations are unavoidable, but they can be modeled. We discuss its relation to the integral constraint and the implications for the galaxy clustering analysis.

Ellipticities of Galaxy Cluster Halos from Halo–Shear–Shear Correlations

Abstract We report the first detection of the halo ellipticities of galaxy clusters by applying the halo–shear–shear correlations (HSSCs), without the necessity of using major axis determination. We use the Fourier_Quad shear catalog based on the Hyper Suprime-Cam Survey and the group catalog from the Dark Energy Spectroscopic Instrument Legacy Surveys for the measurement of group/cluster lensing and HSSC. Our analysis includes off-centering effects. We obtain the average projected ellipticity of dark matter halos with mass 13.5 < log ( M G h / M ⊙ ) < 14.5 within a 1.3 virial radius to be 0.4 8 − 0.19 + 0.12 . We divide the sample into two groups based on mass and redshift, and we find that halos with higher mass tend to exhibit increased ellipticity. We also reveal that high-richness halos have larger ellipticities, confirming the physical picture from numerical simulation that high-richness halos have a dynamical youth and more active mass accretion phase.

Study of Satellite Plane Structure Characteristics Based on TNG50 Simulations: A Comparative Analysis from Plane to Nonplane Structures

Abstract In recent years, multiple plane structures of satellite galaxies have been identified in the nearby Universe, although their formation mechanisms remain unclear. In this work, we employ the TNG50-1 numerical simulation to classify satellite systems into plane and nonplane structures, based on their geometric and dynamical properties. We focus on comparing the characteristics of these plane and nonplane structures. The plane structures in TNG50-1 exhibit a mean height of 5.24 kpc, with most of them found in galaxy groups with intermediate halo virial masses within the narrow range of 1011.5–1012.5 M ⊙. Statistical analyses reveal that plane structures of satellite galaxies constitute approximately 11.30% in TNG50-1, with this proportion increasing to 27.11% in TNG100-1, aligning closely with previous observations. Additionally, central galaxies in clusters and groups hosting corotating plane structures are intermediate massive and slightly metal-poorer than those in nonplane structures. Significant differences are found between in-plane and out-of-plane satellite galaxies, suggesting that in-plane satellites exhibit slightly longer formation times and more active interstellar matter cycles. The satellites within these plane structures in TNG50-1 exhibit similar radial distributions with observations but are fainter and more massive than those in observational plane structures due to the over- or underestimation of galaxy properties in simulations. Our analysis also shows that the satellite plane structures might be affected by some low- or high-mass galaxies temporarily entering the plane structures due to the gravitational potential of the clusters and groups after the plane structures had formed.

X-ray surface brightness fluctuations in smooth galaxy cluster atmospheres

Abstract We measure surface brightness fluctuations in Chandra X-ray images of the cores of the galaxy clusters Abell 2029, Abell 2151, Abell 2107, RBS0533, and RBS0540. Their relatively structureless X-ray atmospheres exhibit the thermodynamic properties of cool cores including short central cooling times and low entropy. However, unlike typical cool-core clusters, molecular gas, star formation, and bubbles associated with radio jets are faint or absent near their central galaxies. Four clusters show typical gas density fluctuation amplitudes of ∼ 10percnt on the scales probed, apart from RBS0540, which exhibits lower amplitudes, suggesting that its gas is mildly disturbed. Under the assumption that gas density fluctuations are indicative of random gas velocities, we estimate scale-dependent velocity amplitudes of gas motions across all studied clusters, which range from 100 $\rm km~s^{-1}$ to 200 $\rm km~s^{-1}$ in Abell 2029, Abell 2151, and Abell 2107. These velocity estimates are comparable to the atmospheric velocity dispersion in the Perseus cluster measured by the Hitomi X-ray Observatory. The turbulent heating rates implied by our measurements are of the same order as the radiative cooling rates. Our results suggest that atmospheric sloshing and perhaps turbulent motion may aid radio jets in stabilizing atmospheric cooling.

COOL-LAMPS. VII. Quantifying Strong-lens Scaling Relations with 177 Cluster-scale Strong Gravitational Lenses in DECaLS

Abstract We estimate the Einstein-radius-enclosed total mass for 177 cluster-scale strong gravitational lenses identified by the ChicagO Optically selected Lenses Located At the Margins of Public Surveys (COOL-LAMPS) collaboration with lens redshifts ranging from 0.2 ⪅ z ⪅ 1.0 using the brightest-cluster-galaxy (BCG) redshift and an observable proxy for the Einstein radius. We constrain the Einstein-radius-enclosed luminosity and stellar mass by fitting parametric spectral energy distributions to aperture photometry from the Dark Energy Camera Legacy Survey (DECaLS) in the g-, r-, and z-band Dark Energy Camera filters. We find that the BCG redshift, enclosed total mass, and enclosed luminosity are strongly correlated and well described by a planar relationship in 3D space. We find that the enclosed total mass and stellar mass are correlated with a logarithmic slope of 0.50 0 − 0.031 + 0.029 , and the enclosed total mass and stellar-to-total mass fraction are correlated with a logarithmic slope of − 0.49 5 − 0.033 + 0.032 . In tandem with the small radii within which these slopes are constrained, this may suggest invariance in baryon conversion efficiency and feedback strength as a function of cluster-centric radii in galaxy clusters. Additionally, the correlations described here should have utility in ranking strong-lensing candidates in upcoming imaging surveys—such as Rubin/Legacy Survey of Space and Time—in which an algorithmic treatment of strong lenses will be needed due to the sheer volume of data these surveys will produce.

A halo model approach for mock catalogs of time-variable strong gravitational lenses

Time delays in both galaxy- and cluster-scale strong gravitational lenses have recently attracted a lot of attention in the context of the Hubble tension. Future wide-field cadenced surveys, such as the LSST, are anticipated to discover strong lenses across various scales. We generate mock catalogs of strongly lensed QSOs and SNe on galaxy-, group-, and cluster-scales based on a halo model that incorporates dark matter halos, galaxies, and subhalos. For the upcoming LSST survey, we predict that approximately 3500 lensed QSOs and 200 lensed SNe with resolved multiple images will be discovered. Among these, about 80 lensed QSOs and 10 lensed SNe will have maximum image separations larger than 10 arcsec, which roughly correspond to cluster-scale strong lensing. We find that adopting the Chabrier stellar IMF instead of the fiducial Salpeter IMF reduces the predicted number of strong lenses approximately by half, while the distributions of lens and source redshifts and image separations are not significantly changed. In addition to mock catalogs of multiple-image lens systems, we create mock catalogs of highly magnified systems, including both multiple-image and single-image systems. We find that such highly magnified systems are typically produced by massive galaxies, but non-negligible fraction of them are located in the outskirt of galaxy groups and clusters. Furthermore, we compare subsamples of our mock catalogs with lensed QSO samples constructed from the SDSS and Gaia to find that our mock catalogs with the fiducial Salpeter IMF reproduce the observation quite well. In contrast, our mock catalogs with the Chabrier IMF predict a significantly smaller number of lensed QSOs compared with observations, which adds evidence that the stellar IMF of massive galaxies is Salpeter-like. Our python code SL-Hammocks as well as the mock catalogs are made available online. (abridged)

Discrepancies between JWST Observations and Simulations of Quenched Massive Galaxies at z > 3: A Comparative Study with IllustrisTNG and ASTRID

Abstract Recent JWST observations have uncovered an unexpectedly large population of massive quiescent galaxies at z > 3. Using the cosmological simulations IllustrisTNG and ASTRID, we identify analogous galaxies and investigate their abundance, formation, quenching mechanisms, and post-quenching evolution for stellar masses 9.5 < log 10 ( M ⋆ / M ⊙ ) < 12 . We apply three different quenching definitions and find that both simulations significantly underestimate the comoving number density of quenched massive galaxies at z ≳ 3 compared to JWST observations by up to ∼2 dex. In both simulations, the high-z quenched massive galaxies often host overmassive central black holes above the local M BH–M ⋆ relation, implying that AGN feedback is key in quenching galaxies in the early Universe. The typical quenching timescales for these galaxies are ∼200–600 Myr. IllustrisTNG primarily employs AGN kinetic feedback, while ASTRID relies on AGN thermal feedback at z > 2.3, which is less effective and has a longer quenching timescale. Although these simulations differ in many aspects, making a direct comparison challenging, our findings suggest the need for improved physical models of AGN feedback in galaxy formation simulations. At lower stellar masses, the quenched galaxies have denser local environments than the star-forming galaxies, suggesting that environmental quenching helps quench less-massive galaxies. We also study the post-quenching evolution of the high-z massive quiescent galaxies and find that many experience subsequent reactivation of star formation, evolving into primary progenitors of z = 0 brightest cluster galaxies.

Directional miscentering dependence in weak lensing mass bias

Abstract Galaxy cluster masses estimated from parametric modeling of weak lensing shear observations are known to be biased by inaccuracies in observationally determined centers. It has recently been shown that such systematic effects can be non-isotropic when centers are derived from X-ray or Compton-Y (Sunyaev-Zeldovich effect) observations, which is often the case in practice. This fact challenges current methods of accurately correcting for weak lensing mass biases using simulations paired with isotropic empirical miscentering distributions, in particular as the effect on determined masses is currently a dominant source of systematic uncertainty. We use hydrodanamical cosmological simulations taken from the Magneticum Pathfinder simulations to show that the non-isotropic component of the mass bias can be reduced to within one percent of the mass when considering the center of mass, rather than the bottom of the gravitational potential, as the reference center of a galaxy cluster.

A MOND model applied to the rotation curve of galaxies

In this work, we propose a modified Newton dynamics (MOND) model to study the rotation curves of galaxies. The model is described by an arc-tangent interpolating function and it fits the rotation curves of several galaxies without invoking the presence of dark matter. We took from the literature the rotation curve data of 15 spiral galaxies, and used it to constrain the model parameter, [Formula: see text], as around [Formula: see text] [Formula: see text]m/s2. This parameter is also called the acceleration constant once it gives the acceleration scale where Newton’s dynamics fails. The model can be further tested in different astrophysical scenarios, such as, the missing mass problem of galaxy clusters and the accelerated expansion of the Universe, thus leading to a more robust and well-constrained model.

Euclid preparation. LXVI. Impact of line-of-sight projections on the covariance between galaxy cluster multi-wavelength observable properties: insights from hydrodynamic simulations

Euclid preparation. LXVI. Impact of line-of-sight projections on the covariance between galaxy cluster multi-wavelength observable properties: insights from hydrodynamic simulations

KiDS-Legacy: Angular galaxy clustering from deep surveys with complex selection effects

Photometric galaxy surveys, despite their limited resolution along the line of sight, encode rich information about the large-scale structure (LSS) of the Universe thanks to the high number density and extensive depth of the data. However, the complicated selection effects in wide and deep surveys can potentially cause significant bias in the angular two-point correlation function (2PCF) measured from those surveys. In this paper, we measure the 2PCF from the newly published KiDS-Legacy sample. Given an r-band $5σ$ magnitude limit of $24.8$ and survey footprint of $1347$ deg^2, it achieves an excellent combination of sky coverage and depth for such a measurement. We find that complex selection effects, primarily induced by varying seeing, introduce over-estimation of the 2PCF by approximately an order of magnitude. To correct for such effects, we apply a machine learning-based method to recover an organised random (OR) that presents the same selection pattern as the galaxy sample. The basic idea is to find the selection-induced clustering of galaxies using a combination of self-organising maps (SOMs) and hierarchical clustering (HC). This unsupervised machine learning method is able to recover complicated selection effects without specifying their functional forms. We validate this SOM+HC method on mock deep galaxy samples with realistic systematics and selections derived from the KiDS-Legacy catalogue. Using mock data, we demonstrate that the OR delivers unbiased 2PCF cosmological parameter constraints, removing the $27σ$ offset in the galaxy bias parameter that is recovered when adopting uniform randoms. Blinded measurements on the real KiDS-Legacy data show that the corrected 2PCF is robust to the SOM+HC configuration near the optimal set-up suggested by the mock tests.

Can Active Galactic Nuclei Activity Be Enhanced by Ram Pressure Stripping?—X-Ray Perspective

Abstract Ram pressure stripping (RPS) is an important process that plays a significant role in shaping the evolution of cluster galaxies and their surrounding environment. Despite its recognized significance, the potential connection between RPS and active galactic nuclei (AGN) activity in cluster galaxies remains poorly understood. Recent claims, based on optical emission-line diagnostics, have suggested such a connection. Here, we investigate this relationship from an X-ray perspective, using a sample of galaxies undergoing RPS in four nearby galaxy clusters: A1656, A1367, A426, and A3627. This study is the first to test such a connection from an X-ray standpoint. Our analysis reveals no signs of enhanced X-ray AGN activity in our sample, with most RPS galaxies (~90%) showing X-ray luminosities below 1041 erg s−1 in their central point sources. Moreover, there is no noticeable difference in X-ray AGN activity among RPS galaxies compared to a control sample of non-RPS galaxies, as demonstrated by the similar X-ray luminosities observed in their central point sources. While the most luminous X-ray AGN in our sample is found in ESO 137-002, a galaxy undergoing RPS in A3627, there is no evidence for a widespread enhancement of X-ray AGN activity due to RPS. Given the limited sample size of our study, this could also indicate that either the X-ray AGN enhancement from RPS is at most weak or the timescale for the X-ray AGN enhancement is short. This emphasizes the need for further investigations with larger X-ray samples to better understand the impact of RPS on AGN activity in cluster galaxies.

Evidence that pre-processing in filaments drives the anisotropic quenching of satellite galaxies in massive clusters

ABSTRACT We use a sample of 11 $z\approx 0.2\!-\!0.5$ ($z_{\text{med.}} = 0.36$) galaxy clusters from the Cluster Lensing And Supernovae survey with Hubble to analyse the angular dependence of satellite galaxy colour $(B-R)$ and passive galaxy fraction ($f_{\text{pass.}}$) with respect to the major axis of the brightest cluster galaxy (BCG). This phenomenon has been dubbed as ‘anisotropic quenching’, ‘angular conformity’ or ‘angular segregation’, and it describes how satellite galaxies along the major axis of the BCG are more likely to be quenched than those along the minor axis. A highly significant anisotropic quenching signal is found for satellites, with a peak in $(B-R)$ and $f_{\text{pass.}}$ along the major axis. We are the first to measure anisotropic quenching out to cluster-centric radii of $3R_{200}$ ($R_{200\text{, med.}} \approx 933$$\mathrm{k}\text{pc}$). We find that the signal is significant out to at least $2.5R_{200}$, and the amplitude of the signal peaks at $\approx 1.25R_{200}$. This is the first time a radial peak of the anisotropic quenching signal has been measured directly. We suggest that this peak could be caused by a build-up of backsplash galaxies at this radius. Finally, we find that $f_{\text{pass.}}$ is significantly higher along the major axis for fixed values of local surface density. The density drops less rapidly along the major axis and so satellites spend more time being pre-processed here compared to the minor axis. We therefore conclude that pre-processing in large-scale structure, and not active galactic nuclei outflows, is the cause of the anisotropic quenching signal in massive galaxy clusters, however, this may not be the cause in lower mass haloes.