Massive Clusters Research Articles

Probing the magnetized gas distribution in galaxy groups and the cosmic web with POSSUM Faraday rotation measures

ABSTRACT We present initial results from the Polarization Sky Survey of the Universe’s Magnetism (POSSUM), analysing 22 817 Faraday rotation measures (RMs) with median uncertainties of 1.2 rad m$^{-2}$ across 1520 deg2 to study magnetized gas associated with 55 nearby galaxy groups ($z\lesssim 0.025$) with halo masses between $10^{12.5}$ and $10^{14.0}$ M$_\odot$. We identify two distinct gas phases: the intragroup medium (IGrM) within 0–2 splashback radii and the warm-hot intergalactic medium (WHIM) extending from 2 to 7 splashback radii. These phases enhance the standard deviation of residual (i.e. Galactic foreground RM-subtracted) RMs by $6.9\pm 1.8$ rad m$^{-2}$ and $4.2 \pm 1.2$ rad m$^{-2}$, respectively. Estimated magnetic field strengths are several μG within the IGrM and 0.1–1 μG in the WHIM. We estimate the plasma $\beta$ in both phases, and show that magnetic pressure might be more dynamically important than in the ICM of more massive clusters or sparse cosmic web filaments. Our findings indicate that ‘missing baryons’ in the WHIM likely extend beyond the gravitational radii of group-mass haloes to Mpc scales, consistent with large-scale, outflow-driven ‘magnetized bubbles’ seen in cosmological simulations. We demonstrate that RM grids are an effective method for detecting magnetized thermal gas at galaxy group interfaces and within the cosmic web. This approach complements X-ray and Sunyaev-Zel’dovich effect methods, and when combined with fast radio burst dispersion measures, data from the full POSSUM survey – comprising approximately a million RMs – will allow direct magnetic field measurements to further our understanding of baryon circulation in these environments and the magnetized universe.

Health-related quality of life of people with type 1 diabetes: An IMI2 SOPHIA post hoc analysis of FUTURE and ADJUNCT-ONE.

To characterize and stratify health-related quality of life in individuals with type 1 diabetes (T1D) using body mass index (BMI) and clustering analysis. Baseline data on individuals with T1D were pooled from two studies. A post hoc analysis of health-related quality of life, measured using the 36-item Short-Form questionnaire, was performed, referenced to the 2010 US general population. Descriptive statistics were presented for the pooled cohort and per BMI category. K-means clustering was performed. One-way analysis of variance was conducted to examine differences in clinical characteristics between clusters. The pooled cohort consisted of 2256 individuals with T1D (age: 45.4 ± 15.0 years, BMI: 26.2 ± 4.6 kg/m2, diabetes duration: 22.7 ± 13.5 years). All quality-of-life domains were slightly lower than 50(the general population's mean), except for vitality. Individuals with a BMI ≥30 kg/m2 reported lower scores for bodily pain, physical functioning, general health, and vitality. A first cluster with a high and a second cluster with a low quality of life were identified, with significant differences in the mental (Cluster 1: 53.8 ± 6.8 vs. Cluster 2: 39.5 ± 10.7; p < 0.001) and physical component summary scores (Cluster 1: 49.6 ± 6.3 vs. Cluster 2: 35.2 ± 12.0; p < 0.001), which exceeded differences found between BMI categories. In our population of people living with T1D, higher BMI may have adversely impacted physical domains of quality of life, but larger differences between the high- and low-quality-of-life cluster indicate that more factors play a role.

Numerical and experimental studies on the motion and deposition of collapsing rock clusters: Effect of rock particle sphericity

In this paper, a series of experimental and numerical tests are carried out to study the effect of rock particle sphericity on the motion and deposition of collapsing rock clusters. To this end, three kinds of typical rock particles with different sphericity (i.e., pebble, rubble and block) are used for experiments and a special laboratory setup that involves a chute with two inclined sections is designed to reproduce their natural motion. Then, a three-dimensional modelling of collapsing rock cluster incorporating rock particles with different sphericity is developed using spherical harmonics function reconstruction. The sphericity of particle effect on the motion and deposition of rock cluster is studied experimentally and numerically in terms of the average velocity and deposition zone. There has a good agreement between them. In addition, some potential factors such as rock particle size, cluster mass and component are investigated and discussed. The obtained results may facilitate the current knowledge on the dynamic behavior of collapsing rock clusters effect of particle sphericity.

The Massive and Distant Clusters of WISE Survey 2: A Stacking Analysis Investigating the Evolution of Star Formation Rates and Stellar Masses in Groups and Clusters

The evolution of galaxies depends on their masses and local environments; understanding when and how environmental quenching starts to operate remains a challenge. Furthermore, studies of the high-redshift regime have been limited to massive cluster members, owing to sensitivity limits or small fields of view when the sensitivity is sufficient, intrinsically biasing the picture of cluster evolution. In this work, we use stacking to investigate the average star formation history of more than 10,000 groups and clusters drawn from the Massive and Distant Clusters of WISE Survey 2. Our analysis covers near-ultraviolet to far-infrared wavelengths, for galaxy overdensities at 0.5 ≲ z ≲ 2.54. We employ spectral energy distribution fitting to measure the specific star formation rates (sSFRs) in four annular apertures with radii between 0 and 1000 kpc. At z ≳ 1.6, the average sSFR evolves similarly to the field in both the core and the cluster outskirts. Between z¯=1.60 and z¯=1.35 , the sSFR in the core drops sharply, and it continues to fall relative to the field sSFR at lower redshifts. We interpret this change as evidence that the impact of environmental quenching dramatically increases at z ∼ 1.5, with the short time span of the transition suggesting that the environmental quenching mechanism dominant at this redshift operates on a rapid timescale. We find indications that the sSFR may decrease with increasing host halo mass, but lower-scatter mass tracers than the signal-to-noise ratio are needed to confirm this relationship.

Relativistic SZ temperatures and hydrostatic mass bias for massive clusters in the FLAMINGO simulations

ABSTRACT The relativistic Sunyaev-Zel’dovich (SZ) effect can be used to measure intracluster gas temperatures independently of X-ray spectroscopy. Here, we use the large-volume FLAMINGO simulation suite to determine whether SZ y-weighted temperatures lead to more accurate hydrostatic mass estimates in massive ($M_{\rm 500c} \gt 7.5\times 10^{14}\, {\rm M}_{\odot }$) clusters than when using X-ray spectroscopic-like temperatures. We find this to be the case, on average. The median bias in the SZ mass at redshift zero is $\left\langle b \right\rangle \equiv 1-\left\langle M_{\rm 500c,hse}/M_{\rm 500c,true} \right\rangle = -0.05 \pm 0.01$, over 4 times smaller in magnitude than the X-ray spectroscopic-like case, $\left\langle b \right\rangle = 0.22 \pm 0.01$. However, the scatter in the SZ bias, $\sigma _{b} \approx 0.2$, is around 40 per cent larger than for the X-ray case. We show that this difference is strongly affected by clusters with large pressure fluctuations, as expected from shocks in ongoing mergers. Selecting the clusters with the best-fitting generalized NFW pressure profiles, the median SZ bias almost vanishes, $\left\langle b \right\rangle = -0.009 \pm 0.005$, and the scatter is halved to $\sigma _{b} \approx 0.1$. We study the origin of the SZ/X-ray difference and find that, at $R_{\rm 500c}$ and in the outskirts, SZ weighted gas better reflects the hot, hydrostatic atmosphere than the X-ray weighted gas. The SZ/X-ray temperature ratio increases with radius, a result we find to be insensitive to variations in baryonic physics, cosmology, and numerical resolution.

Spatial segregation of massive clusters in a simulation of colliding dwarf galaxies

The collective properties of star clusters are investigated using a simulation of the collision between two dwarf galaxies. The characteristic power law of the cluster mass function, N(M), with a logarithmic slope dN/dM ~ -1, is present from cluster birth and remains throughout the simulation. The maximum mass of a young cluster scales with the star formation rate (SFR). The relative average minimum separation, R(M)= N(M)^{1/p}D_min(M)/D(M_low), for average minimum distance D_min(M) between clusters of mass M, and for lowest mass, M_low, measured in projection (p=2) or three dimensions (p=3), has a negative slope, d log R/d log M ~ -0.2, for all masses and ages. This agrees with observations of R(M) in low-mass galaxies studied previously. Like the slope of N(M), R(M) is apparently a property of cluster birth for dwarf galaxies that does not depend on SFR or time. The negative slope for R(M) implies that massive clusters are more concentrated relative to lower mass clusters throughout the entire mass range. Cluster growth through coalescence is also investigated. The ratio of the kinetic to potential energy of all near-neighbor clusters is generally large, but a tail of low values in the distribution of this ratio suggests that a fraction of the clusters merge, ~8% by number throughout the ~300 Myr of the simulation and up to 60% by mass for young clusters in their first 10 Myr, scaling with the SFR above a certain threshold.

A morphological analysis of the galaxy cluster XLSSC 122 at z=1.98

Abstract We present a morphological analysis of 29 spectroscopically confirmed members of XLSSC 122, a massive galaxy cluster at z = 1.98. We perform photometry using Statmorph on images of the cluster members from the Hubble Space Telescope (HST) Wide Field Camera (WFC3) in the F140W band. We visually assess the images and compute non-parametric morphological measures, namely the concentration C, asymmetry A, Gini and M20 values and use them to classify cluster members as either being bulge-dominated, disk-dominated or presenting possible merger features. The morphological properties of the XLSSC 122 members show clear evidence of bimodality. The bulge-dominated galaxies are redder, older and are found in the denser regions of the cluster, while the galaxies showing disturbed features are bluer, younger and are found towards the outskirts of the cluster. XLSSC 122 is also found to be deficient in blue and disturbed galaxies compared to field galaxy populations from the CANDELS/3D-HST surveys. An analysis of merger events occurring in numerical simulations suggest that galaxy interactions generating a population of morphologically disturbed galaxies in XLSSC 122 may have occurred over the interval 2 &amp;lt; z &amp;lt; 3, i.e. prior to their infall into the virial core of the cluster.

A complex node of the cosmic web associated with the massive galaxy cluster MACS J0600.1-2008

ABSTRACT MACS J0600.1-2008 (MACS0600) is an X-ray-luminous, massive galaxy cluster at $z_{\mathrm{d}}=0.43$, studied previously by the REionization LensIng Cluster Survey and ALMA Lensing Cluster Survey projects which revealed a complex, bimodal mass distribution and an intriguing high-redshift object behind it. Here, we report on the results of a combined analysis of the extended strong lensing (SL), X-ray, Sunyaev–Zeldovich (SZ), and galaxy luminosity-density properties of this system. Using new JWST and ground-based Gemini-N and Keck data, we obtain 13 new spectroscopic redshifts of multiply-imaged galaxies and identify 12 new photometric multiple-image systems and candidates, including two multiply-imaged $z\sim 7$ objects. Taking advantage of the larger areal coverage, our analysis reveals an additional bimodal, massive SL structure which we measure spectroscopically to lie adjacent to the cluster and whose existence was implied by previous SL-modelling analyses. While based in part on photometric systems identified in ground-based imaging requiring further verification, our extended SL model suggests that the cluster may have the second-largest critical area and effective Einstein radius observed to date, $A_{\mathrm{crit}}\simeq 2.16\, \mathrm{arcmin}^2$ and $\theta _{\mathrm{E}}=49.7^{\prime \prime }\pm 5.0^{\prime \prime }$ for a source at $z_{\mathrm{s}}=2$, enclosing a total mass of $M(\lt \theta _{\mathrm{E}})=(4.7\pm 0.7)\times 10^{14}\, \mathrm{M}_{\odot }$. These results are also supported by the galaxy luminosity distribution, and the SZ and X-ray data. Yet another, probably related massive cluster structure, discovered in X-rays 5 arcmin (1.7 Mpc) further north, suggests that MACS0600 is part of an even larger filamentary structure. This discovery adds to several recent detections of massive structures around SL galaxy clusters and establishes MACS0600 as a prime target for future high-redshift surveys with JWST.

Catalytic coagulation.

We introduce an autocatalytic aggregation model in which the rate at which two clusters merge is controlled by the third "catalytic" cluster, whose mass must equal the mass of one of the reaction partners. The catalyst is unaffected by the joining event and can participate in or catalyze subsequent reactions. This model is meant to mimic the self-replicating reactions that occur in models for the origin of life. We solve the kinetics of catalytic coagulation for the case of mass-independent reaction rates and show that the total cluster density decays as t^{-1/3}, while the density of clusters of fixed mass decays as t^{-2/3}. These behaviors contrast with the corresponding t^{-1} and t^{-2} scalings for classic aggregation. We extend our model to mass-dependent reaction rates, to situations where only "magic" mass clusters can catalyze reactions, and to include steady monomer input.

Diverse Oxygen Abundance in Early Galaxies Unveiled by Auroral Line Analysis with JWST

We present deep JWST NIRSpec observations in the sight line of MACS J1149.5+2223, a massive cluster of galaxies at z = 0.54. We report the spectroscopic redshift of 28 sources at 3 < z < 9.1, including nine sources with the detection of the OIIIλ4363 auroral line. Combining these with 16 OIIIλ4363 -detected sources from publicly available JWST data, our sample consists of 25 galaxies with robust gas-phase metallicity measurements via the direct method. We observe a positive correlation between stellar mass and metallicity, with an ∼0.5 dex offset down below the local relation. Interestingly, we find a larger-than-expected scatter of ∼0.3 dex around the relation, which cannot be explained by redshift evolution among our sample or other third parameters. The scatter increases at higher redshift, and we tentatively attribute this to the enrichment process having higher stochasticity, due to shallower potential wells, more intense feedback processes, and a higher galaxy merger rate. Despite reaching a considerably low-mass regime ( logM*/M⊙∼7.3 ), our samples have metallicity of log(O/H) +12 ≳ 7, i.e., comparable to the most metal-poor galaxies in the local Universe. The search for primordial galaxies may be accomplished by extending toward a lower mass and/or by investigating inhomogeneities at smaller spatial scales. Lastly, we investigate potential systematics caused by the limitation of JWST’s Micro-Shutter Assembly observations. Caution is warranted when the target exceeds the slit size, as this situation could allow an overestimation of global metallicity, especially under the presence of a strong negative metallicity gradient.

The Impact of Stellar Radiative Feedback on Formation of Young Massive Clusters via Fast H i Gas Collisions

Young massive clusters (YMCs) are dense aggregates of young stars and are often speculated as potential precursors to globular clusters. However, the formation mechanism of massive and compact gas clumps that precede YMCs remains unknown. In this paper, we study the formation of such massive clumps via fast H i gas collisions (∼100 km s−1) as suggested by recent observations and their subsequent evolution into YMCs by using three-dimensional magnetohydrodynamics simulations involving self-gravity and detailed thermal/chemical processes. In particular, the impact of ionization feedback from stellar radiation is included in an approximate fashion where the temperature within the H ii regions is elevated to 10,000 K, while supernova feedback is not included. We examine whether the resulting massive clumps can survive this ionization feedback and evolve into YMCs. Our simulations reveal the emergence of gas clumps that not only possess substantial mass (∼105 M ⊙) but also sufficient compactness (∼5 pc). Notably, these clumps exhibit significantly higher escape velocities compared to the sound speed of the H ii region, indicating effective gravitational retention of gas against feedback-induced evaporation. Consequently, these conditions foster efficient star formation within the massive gas clumps, ultimately leading to their evolution into YMCs. We also perform simulations involving lower-velocity gas collisions, approximately 15 km s−1, typical shock velocities induced by galactic superbubbles. In contrast to the high-velocity collisions, we find that molecular cloud formation does not occur in the case of 1 cm−3 gas collision, while YMC formation is observed in the presence of denser gas of 10 cm−3. However, the formation of YMCs requires compression periods exceeding 10 Myr in these cases, indicating a potential preference for gas collisions driven by intergalactic interactions rather than galactic superbubbles for YMC formation.

Resolving high-z galaxy cluster properties through joint X-ray and millimeter analysis: Case study of SPT-CLJ0615-5746

We present a joint millimetric and X-ray analysis of hot gas properties in the distant galaxy cluster SPT-CLJ0615-5746 (z = 0.972). Combining Chandra observations with the South Pole Telescope (SPT) and Planck data, we performed radial measurements of thermodynamical quantities up to a characteristic radius of 1.2 R500. We exploited the high angular resolution of Chandra and SPT to map the innermost region of the cluster and the high sensitivity to the larger angular scales of Planck to constrain the outskirts and improve the estimation of the cosmic microwave background and the galactic thermal dust emissions. In addition to maximizing the accuracy of radial temperature measurements, our joint analysis allows us to test the consistency between X-ray and millimetric derivations of thermodynamic quantities via the introduction of a normalization parameter (ηT) between X-ray and millimetric temperature profiles. This approach reveals a substantial high value of the normalization parameter, ηT = 1.45−0.18+0.17, suggesting that the gas halo is aspherical. Assuming hot gas hydrostatic equilibrium within complementary angular sectors that intercept the major and minor elongation of the X-ray image, we infer a halo mass profile that results from an effective compensation of azimuthal variations of gas densities by variations in the ηT parameter. Consistent with earlier integrated X-ray and millimetric measurements, we infer a cluster mass of M500HE = 10.67−0.50+0.62 1014 M⊙.

The SRG/eROSITA All-Sky Survey

Galaxy cluster gas temperatures (T) play a crucial role in many cosmological and astrophysical studies. However, it has been shown that T measurements can significantly vary between different X-ray telescopes. These T biases can propagate to several cluster applications in which T can be used, such as measuring hydrostatic cluster masses and constraining the angular variation of cosmological parameters. Thus, it is important to accurately cross-calibrate X-ray instruments to account for systematic biases. In this work, we present the cross-calibration between Spectrum Roentgen Gamma/eROSITA (SRG/eROSITA) and Chandra/ACIS and between SRG/eROSITA and XMM-Newton/EPIC using for the first time a large sample of galaxy cluster T. To do so, we used the first eROSITA All-Sky Survey data and the preliminary extremely expanded HIgh FLUx Galaxy Cluster Sample, a large X-ray flux-limited cluster catalog. We spectroscopically measured X-ray T for 186 independent cluster regions with both SRG/eROSITA and Chandra/ACIS in a self-consistent way for three energy bands: 0.7–7 keV (full), 0.5–4 keV (soft), and 1.5–7 keV (hard). We did the same with SRG/eROSITA and XMM-Newton/EPIC for 71 different cluster regions and all three bands. We find that SRG/eROSITA measures systematically lower T than the other two instruments, with hotter clusters deviating more than cooler ones. For the full band, SRG/eROSITA returns 20% and 14% lower T than Chandra/ACIS and XMM-Newton/EPIC, respectively, when the two other instruments each measure kBT ≈ 3 keV. The discrepancy respectively increases to 38% and 32% when Chandra/ACIS and XMM-Newton/EPIC each measure kBT ≈ 10 keV. On the other hand, the discrepancy becomes milder for low-T galaxy groups. Moreover, a broken power law fit demonstrated that there is a break at the SRG/eROSITA-Chandra/ACIS scaling relation at kBT ≈ 1.7 − 2.7 keV, depending on the energy band. The soft band shows a marginally lower discrepancy compared to the full band. In the hard band, the cross-calibration of SRG/eROSITA and the other instruments show very strong differences. We tested several possible systematic biases (such as multiphase cluster gas, Galactic absorption, non-Gaussian scatter, and selection effects) to identify the reason behind the cross-calibration discrepancies, but none could significantly alleviate the tension. For now, it is most likely that the systematically lower SRG/eROSITA T can be attributed to systematic effective area calibration uncertainties; however, the exact role of multiphase cluster gas in the observed T discrepancies needs to be further investigated. Furthermore, we provide conversion factors between SRG/eROSITA, Chandra/ACIS, and XMM-Newton/EPIC T that will be beneficial for future cluster studies that combine SRG/eROSITA T with data from other X-ray instruments. Finally, we also provide conversion functions between the official eRASS1 cluster catalog T and the equivalent core and core-excised Chandra/ACIS and XMM-Newton/EPIC T.

The SRG/eROSITA All-Sky Survey: Exploring halo assembly bias with X-ray-selected superclusters

Numerical simulations indicate that the clustering of dark matter halos is not only dependent on the halo masses but has a secondary dependence on other properties, such as the assembly history of the halo. This phenomenon, known as the halo assembly bias (HAB), has been found mostly on galaxy scales; observational evidence on larger scales is scarce. In this work, we propose a novel method for exploring HAB on cluster scales using large samples of superclusters. Leveraging the largest-ever X-ray galaxy cluster and supercluster samples obtained from the first SRG/eROSITA all-sky survey, we constructed two subsamples of galaxy clusters that consist of supercluster members and isolated clusters, respectively. After correcting for the selection effects on redshift, mass, and survey depth, we computed the excess in the concentration of the intracluster gas of isolated clusters with respect to supercluster members, defined as δcgas ≡ cgas, ISO/cgas, SC − 1, to investigate the environmental effect on the concentration of clusters, a sign of HAB on cluster scales. We find that the average gas mass concentration of isolated clusters is a few percent higher than that of supercluster members, with a maximum significance of 2.8σ. The result for δcgas varies with the overdensity ratio, f, in supercluster identification, cluster mass proxies, and mass and redshift ranges but remains positive in almost all the measurements. We measure slightly larger δcgas when adopting a higher f for supercluster identification. The δcgas is also higher for low-mass and low-redshift clusters. We performed weak lensing analyses to compare the total mass concentration of the two classes and find a similar trend in total mass concentration as obtained from the gas mass concentration. Our results are consistent with the prediction of HAB on cluster scales, where halos located in denser environments are less concentrated; this trend is stronger for halos with lower masses and at lower redshifts. These phenomena can be explained by the fact that clusters in denser environments, such as superclusters, have experienced more mergers than isolated clusters in their assembling history. This work paves the way to explore HAB with X-ray superclusters and demonstrates that large samples of superclusters with X-ray and weak-lensing data can advance our understanding of the evolution of the large-scale structure.

OMEGACat. II. Photometry and Proper Motions for 1.4 Million Stars in Omega Centauri and Its Rotation in the Plane of the Sky

Omega Centauri (ω Cen) is the most massive globular cluster of the Milky Way. It is thought to be the nucleus of an accreted dwarf galaxy because of its high mass and its complex stellar populations. To decipher its formation history and study its dynamics, we created the most comprehensive kinematic catalog for its inner region, by analyzing both archival and new Hubble Space Telescope (HST) data. Our catalog contains 1,395,781 proper-motion measurements out to the half-light radius of the cluster ( ∼5.0′ ) and down to m F625W ≈ 25 mag. The typical baseline for our proper-motion measurements is 20 yr, leading to a median 1D proper motion precision of ∼11 μas yr−1 for stars with m F625W ≈ 18 mag, with even better precision (∼6.6 μas yr−1) achieved in the extensively observed centermost ( r<1.5′ ) region. In addition to our astrometric measurements, we also obtained precise HST photometry in seven filters spanning from the ultraviolet to the near-infrared. This allows detailed color–magnitude diagram studies and separation of the multiple stellar populations of the cluster. In this work, we describe the data reduction used to obtain both the photometric and the proper-motion measurements. We also illustrate the creation and the content of our catalog, which is made publicly available. Finally, we present measurements of the plane-of-sky rotation of ω Cen in the previously unprobed inner few arcminutes and a precise measurement of the inclination, i = 43.°9 ± 1.°3.

Unraveling the birthplaces of NGC 2070’s massive stars, tracked with MUSE and revealed with JWST

The formation of massive O-type stars cannot be simply explained as a scaled-up version of the accretion mechanisms observed in lower-mass stars. Understanding these processes necessitates systematic studies of their early stages, which are challenging to identify. Forming massive stars remain embedded in their dense nursery clouds, and IR instruments with high spatial resolution capabilities are needed to better observe them. Despite these challenges, MUSE optical observations of the massive cluster NGC 2070 successfully detected potential star-forming regions through spatially resolved electron density maps. To further explore these regions, the James Webb Space Telescope (JWST) utilized its NIRCam and MIRI instruments to penetrate optically obscured areas. This study examines two specific regions in the southeast part of the NGC 2070 MUSE density map, where tracks of highly dense point sources were identified. NIRCam, partially overlapped with MIRI, resolved these MUSE findings, revealing a procession of stellar point sources in the projected images. The detections are associated with elongated clouds, suggesting greater proper motions compared to the surrounding interstellar medium. These findings may indicate the presence of runaway candidates in the early stages of their evolution that are following common escape routes. This would support the notion that dynamical ejection is an efficient mechanism for the formation of massive runaway stars during early stages and likely plays a significant role in the origin of O-type field stars. However, additional data are required to confirm this scenario and rule out other ionizing feedback mechanisms, such as those observed in the formation of pillar-like structures around HII regions in the Milky Way. MUSE electron density mapping effectively captures the complexity of NGC 2070’s interstellar medium and highlights targets for subsequent spectroscopic follow-ups, as demonstrated by the JWST data in the two fields studied.

A measurement of cluster masses using Planck and SPT-SZ CMB lensing

A measurement of cluster masses using Planck and SPT-SZ CMB lensing

The Galaxy–Galaxy Strong Lensing Cross Section and the Internal Distribution of Matter in ΛCDM Substructure

Strong gravitational lensing offers a powerful probe of the detailed distribution of matter in lenses, while magnifying and bringing faint background sources into view. Observed strong lensing by massive galaxy clusters, which are often in complex dynamical states, has also been used to map their dark matter (DM) substructures on smaller scales. Deep high-resolution imaging has revealed the presence of strong lensing events associated with these substructures, namely galaxy-scale sub-halos. However, an inventory of these observed galaxy–galaxy strong lensing (GGSL) events is noted to be discrepant with state-of-the-art ΛCDM simulations. Cluster sub-halos appear to be over-concentrated compared to their simulated counterparts yielding an order-of-magnitude higher value of GGSL. In this paper, we explore the possibility of resolving this observed discrepancy by redistributing the mass within observed cluster sub-halos in ways that are consistent within the ΛCDM paradigm of structure formation. Lensing mass reconstructions from data provide constraints on the mass enclosed within apertures and are agnostic to the detailed mass profile within them. Therefore, as the detailed density profile within cluster sub-halos currently remains unconstrained by data, we are afforded the freedom to redistribute the enclosed mass. We investigate if rearranging the mass to a more centrally concentrated density profile helps alleviate the GGSL discrepancy. We report that refitting cluster sub-halos to the ubiquitous ΛCDM-motivated Navarro–Frenk–White profile, and further modifying them to include significant baryonic components, does not resolve this tension. A resolution to this persisting GGSL discrepancy may require more careful exploration of alternative DM models.

OMEGACat. III. Multiband Photometry and Metallicities Reveal Spatially Well-mixed Populations within ω Centauri’s Half-light Radius

ω Centauri, the most massive globular cluster in the Milky Way, has long been suspected to be the stripped nucleus of a dwarf galaxy that fell into the Galaxy a long time ago. There is considerable evidence for this scenario including a large spread in metallicity and an unusually large number of distinct subpopulations seen in photometric studies. In this work, we use new Multi-Unit Spectroscopic Explorer spectroscopic and Hubble Space Telescope photometric catalogs to investigate the underlying metallicity distributions as well as the spatial variations of the populations within the cluster up to its half-light radius. Based on 11,050 member stars, the [M/H] distribution has a median of (−1.614 ± 0.003) dex and a large spread of ∼1.37 dex, reaching from −0.67 to −2.04 dex for 99.7% of the stars. In addition, we show the chromosome map of the cluster, which separates the red giant branch stars into different subpopulations, and analyze the subpopulations of the most metal-poor component. Finally, we do not find any metallicity gradient within the half-light radius, and the different subpopulations are well mixed.

Cluster population demographics in NGC 628 derived from stochastic population synthesis models

ABSTRACT The physical properties of star cluster populations offer valuable insights into their birth, evolution, and disruption. However, individual stars in clusters beyond the nearest neighbours of the Milky Way are unresolved, forcing analyses of star cluster demographics to rely on integrated light, a process fraught with uncertainty. Here, we infer the demographics of the cluster population in the benchmark galaxy NGC 628 using data from the Legacy Extra-galactic UV Survey (LEGUS) coupled to a novel Bayesian forward-modelling technique. Our method analyses all 1178 clusters in the LEGUS catalogue, $\sim 4$ times more than prior studies severely affected by completeness cuts. Our results indicate that the cluster mass function is either significantly steeper than the commonly observed slope of $-2$ or is truncated at $\approx 10^{4.5}$ M$_\odot$; the latter possibility is consistent with proposed relations between truncation mass and star formation surface density. We find that cluster disruption is relatively mild for the first $\approx 200$ Myr of cluster evolution; no evidence for mass-dependent disruption is found. We find suggestive but not incontrovertible evidence that inner galaxy clusters may be more prone to disruption and outer galaxy clusters have a more truncated mass function, but confirming or refuting these findings will require larger samples from future observations of outer galaxy clusters. Finally, we find that current stellar track and atmosphere models, along with common forms for cluster mass and age distributions, cannot fully capture all features in the multidimensional photometric distribution of star clusters. While our forward-modelling approach outperforms earlier backward-modelling approaches, some systematic differences persist between observed and modelled photometric distributions.