Coma Cluster Research Articles

Dwarf galaxies in the MATLAS Survey: Hubble Space Telescope observations of the globular cluster systems of 74 ultra-diffuse galaxies

Ultra-diffuse galaxies (UDGs), characterised by their low surface brightness and large physical size, constitute a subclass of dwarf galaxies that challenge our current understanding of galaxy formation and evolution. In this paper, we probe the properties of 74 UDGs, identified in the MATLAS survey, based on a comprehensive study of their globular cluster (GC) populations. We obtained high-resolution HST imaging of these galaxies using the ACS F606W and F814W filters, which allowed us to select GCs on the basis of the colour and concentration index. After a background subtraction and completeness correction, we calculated an overall total of 387 GCs. The number of GCs per galaxy ranges from 0 to 38, with the majority (64%) having low counts (0 − 2 GCs). On average, the more massive UDGs tend to host a larger number of GCs. We find that our UDGs have specific frequencies (SN) ranging from 0 to 91, with a small population (9%) having SN > 30. The median SN of our sample is similar to the one for the Perseus cluster UDGs, despite the fact that our UDGs are found in lower density environments. The SN measurements for individual galaxies can extend beyond those found in Perseus, but remain below the values found for UDGs in the Virgo and Coma cluster. Based on a trending analysis of the SN values with the host galaxy properties, we find trends with host galaxy size, roundness, colour, and local density. For the UDGs with sufficiently high statistics, we studied 2D density maps of the GC distributions, which display a variety of appearances: symmetric, asymmetric, off-centre, and elongated. The UDGs with disturbed density maps also show disturbed stellar light morphologies. We further quantified the distribution by modelling it with a Sérsic profile, finding Re, GC/Re, gal ∼ 1.0, which indicates that the GCs follow the stellar light of the host galaxy.

The PIPER survey. II. The globular cluster systems of low surface brightness galaxies in the Perseus cluster

ABSTRACT We present Hubble Space Telescope ACS/WFC and WFC3/UVIS imaging for a sample of 50 low-surface brightness (LSB) galaxies in the $\sim 10^{15}$ M$_{\odot }$ Perseus cluster, which were originally identified in ground-based imaging. We measure the structural properties of these galaxies and estimate the total number of globular clusters (GCs) they host. Around half of our sample galaxies meet the strict definition of an ultra-diffuse galaxy (UDG), while the others are UDG-like but are either somewhat more compact or slightly brighter. A small number of galaxies reveal systems with many tens of GCs, rivalling some of the richest GC systems known around UDGs in the Coma cluster. We find the sizes of rich GC systems, in terms of their half-number radii, extending to $\sim$1.2 times the half-light radii of their host galaxy on average. The mean colours of the GC systems are the same, within the uncertainties, as those of their host galaxy stars. This suggests that GCs and galaxy field stars may have formed at the same epoch from the same enriched gas. It may also indicate a significant contribution from disrupted GCs to the stellar component of the host galaxy as might be expected in the ‘failed galaxy’ formation scenario for UDGs.

The K s -band Luminosity Function of the Rich Cluster VC04 in the Vela Supercluster

To learn more about the properties of the Vela Supercluster (VSCL), located behind the Milky Way at cz ∼ 18,000 km s−1, we determine the K s -band luminosity function (LF) of VC04, the richest known galaxy cluster in the VSCL, and two other VSCL clusters (VC02 and VC08). The galaxy sample is based on NIR observations that are complete to an extinction-corrected absolute magnitude of MKso<−21.ͫ5 (∼2.ͫ5 below MK* ), within the clustercentric radius of r c < 1.5 Mpc (∼70% of the Abell radius). For VC04, we obtained 90 new spectroscopic redshifts of galaxies, observed with the 11 m Southern African Large Telescope. We found the Schechter parameters of the VC04 LF to be M* = −24.ͫ41 ± 0.44, α = −1.10 ± 0.20, and ϕ* = 8.84 ± 0.20. Both the redshift data and the LF confirm VC04 to be a rich but not yet fully relaxed cluster. We independently determined the LF of VC04 on membership defined by the red-sequence method and demonstrated that this method can be used in the absence of high spectroscopic coverage over a cluster. This allowed us to determine the LFs of VC02 and VC08. We also derived the LFs of the Coma, Norma, and Virgo clusters to similar depth and extent as the VSCL clusters. We found that the Schechter parameters of VC04 are within 1σ uncertainties of these local clusters, as well as VC02 and VC08. We do not find significant differences between the LFs in the different cluster environments probed in this work down to MK*+2.ͫ5 .

A detailed study of dwarf galaxies in the core of the Coma Cluster

A detailed study of dwarf galaxies in the core of the Coma Cluster

Simulations of cluster ultra-diffuse galaxies in MOND

Ultra-diffuse galaxies (UDGs) in the Coma cluster have velocity dispersion profiles that are in full agreement with the predictions of modified Newtonian dynamics (MOND) in isolation. However, the external field effect (EFE) from the cluster seriously undermines this agreement. It has been suggested that this could be related to the fact that UDGs are out-of-equilibrium objects whose stars have been heated by the cluster tides or that they recently fell onto the cluster on radial orbits; thus, their velocity dispersion may not reflect the EFE at their instantaneous distance from the cluster centre. In this work, we simulated UDGs within the Coma cluster in MOND, using the Phantom of Ramses ( por ) code. We show that if UDGs are initially at equilibrium within the cluster, tides are not sufficient to increase their velocity dispersions to values as high as the observed ones. On the other hand, if they are on a first radial infall onto the cluster, they can keep high-velocity dispersions without being destroyed until their first pericentric passage. We conclude that in the context of MOND, and without alterations (e.g. a screening of the EFE in galaxy clusters or much higher baryonic masses than currently estimated), we find that UDGs must be out-of-equilibrium objects on their first infall onto the cluster, .

The FLAMINGO simulation view of cluster progenitors observed in the epoch of reionization with JWST

ABSTRACT Motivated by the recent JWST discovery of galaxy overdensities during the Epoch of Reionzation, we examine the physical properties of high-z protoclusters and their evolution using the Full-hydro Large-scale structure simulations with All-sky Mapping for the Interpretation of Next Generation Observations (FLAMINGO) simulation suite. We investigate the impact of the apertures used to define protoclusters, because the heterogeneous apertures used in the literature have limited our understanding of the population. Our results are insensitive to the uncertainties of the subgrid models at a given resolution, whereas further investigation into the dependence on numerical resolution is needed. When considering galaxies more massive than $M_\ast \, {\simeq }\, 10^8\, {\rm M_\odot }$, the FLAMINGO simulations predict a dominant contribution from progenitors similar to those of the Coma cluster to the cosmic star formation rate density during the reionization epoch. Our results indicate the onset of suppression of star formation in the protocluster environments as early as $z\, {\simeq }\, 5$. The galaxy number density profiles are similar to NFW (Navarro–Frenk–White profile) at $z\, {\lesssim }\, 1$ while showing a steeper slope at earlier times before the formation of the core. Different from most previous simulations, the predicted star formation history for individual protoclusters is in good agreement with observations. We demonstrate that, depending on the aperture, the integrated physical properties including the total (dark matter and baryonic) mass can be biased by a factor of 2 to 5 at $z\, {=}\, 5.5$–7, and by an order of magnitude at $z\, {\lesssim }\, 4$. This correction suffices to remove the ${\simeq }\, 3\, \sigma$ tensions with the number density of structures found in recent JWST observations.

Distortions of the Hubble diagram: Line-of-sight signatures of local galaxy clusters

The Universe expansion rate is modulated around local inhomogeneities due to their gravitational potential. Velocity waves are then observed around galaxy clusters in the Hubble diagram. This paper studies them in a ∼738 Mpc-wide, 20483-particle cosmological simulation of our cosmic environment (a.k.a. CLONE: Constrained LOcal &amp; Nesting Environment Simulation). For the first time, the simulation shows that velocity waves that arise in the lines of sight of the most massive dark matter halos agree with those observed in local galaxy velocity catalogs in the lines of sight of Coma and several other local (Abell) clusters. For the best-constrained clusters such as Virgo and Centaurus – that is, those closest to us – secondary waves caused by galaxy groups, further into the non-linear regime, also stand out. This match was not utterly expected given that before being evolved into a fully non-linear z = 0 state, assuming ΛCDM, CLONE initial conditions are constrained solely with linear theory, the power spectrum, and highly uncertain and sparse local peculiar velocities. Additionally, Gaussian fits to velocity wave envelopes show that wave properties are tightly tangled with cluster masses. This link is complex, though, and involves the environment and formation history of the clusters. A proposed metric, measuring the distance between the observed and several re-centred simulated lines of sight, waves included, is shown to be capable of providing a tight mass range estimate for massive local clusters. Using machine learning techniques to grasp more thoroughly the complex wave-mass relation, velocity waves could in the near future be used to provide additional and independent mass estimates from galaxy dynamics within large cluster radii.

A pilot search for MeV gamma-ray emission from five galaxy clusters using archival COMPTEL data

We search for MeV gamma-ray emission between 0.75–30 MeV from five galaxy clusters, viz. Coma, VIRGO, SPT-CL J2012-5649, Bullet, and El Gordo, using archival data from the COMPTEL telescope. For this purpose we use three search templates: point source, radial disk and radial Gaussian. We do not detect any signals from Coma, SPT-CL J2012-5649, Bullet and El Gordo clusters with the 95% c.l. photon energy flux limit ∼ 10-10erg/cm2/s.For VIRGO, we detect a non-zero signal between 0.75 to 1.50 MeV having marginal significance of about 2.5σ, with the observed energy flux equal to ∼ 10-9 ergs/cm2/s. However, we do not confirm the previously reported evidence in literature for a gamma-ray line from Coma and VIRGO clusters between 5–7 MeV.

ELUCID. VIII. Simulating the Coma Galaxy Cluster to Calibrate Model and Understand Feedback

We conducted an investigation of the Coma cluster of galaxies by running a series of constrained hydrodynamic simulations with GIZMO-SIMBA and GADGET-3 based on initial conditions reconstructed from the SDSS survey volume in the ELUCID project. We compared simulation predictions and observations for galaxies, intracluster medium (ICM) and intergalactic medium (IGM) in and around the Coma cluster to constrain galaxy formation physics. Our results demonstrate that this type of constrained investigation allows us to probe in more detail the implemented physical processes, because the comparison between simulations and observations is free of cosmic variance and hence can be conducted in a “one-to-one” manner. We found that an increase in the earlier star formation rate and the supernova feedback of the original GIZMO-SIMBA model is needed to match observational data on stellar, interstellar medium, and ICM metallicity. The simulations without active galactic nucleus (AGN) feedback can well reproduce the observational ICM electron density, temperature, and entropy profiles, ICM substructures, and the IGM temperature–density relation, while the ones with AGN feedback usually fail. However, one requires something like AGN feedback to reproduce a sufficiently large population of quiescent galaxies, particularly in low-density regions. The constrained simulations of the Coma cluster thus provide a test bed to understand processes that drive galaxy formation and evolution.

A dusty protocluster surrounding the binary galaxy HerBS-70 at z = 2.3

ABSTRACT We report on deep SCUBA-2 observations at 850 $\mu$m and NOrthern Extended Millimetre Array (NOEMA) spectroscopic measurements at 2 mm of the environment surrounding the luminous, massive (M* ≈ 2 × 1011 M⊙) Herschel-selected source HerBS-70. This source was revealed by previous NOEMA observations to be a binary system of dusty star-forming galaxies at z = 2.3, with the east component (HerBS-70E) hosting an active galactic nucleus. The SCUBA-2 observations detected, in addition to the binary system, 21 sources at &amp;gt;3.5σ over an area of ∼25 square comoving Mpc with a sensitivity of 1σ850 = 0.75 mJy. The surface density of continuum sources around HerBS-70 is three times higher than for field galaxies. The NOEMA spectroscopic measurements confirm the protocluster membership of three of the nine brightest sources through their CO(4–3) line emission, yielding a volume density 36 times higher than for field galaxies. All five confirmed sub-mm galaxies in the HerBS-70 system have relatively short gas depletion times (80−500 Myr), indicating the onset of quenching for this protocluster core due to the depletion of gas. The dark matter halo mass of the HerBS-70 system is estimated around 5 × 1013 M⊙, with a projected current-day mass of 1015 M⊙, similar to the local Virgo and Coma clusters. These observations support the claim that DSFGs, in particular the ones with observed multiplicity, can trace cosmic overdensities.

NSCs from groups to clusters: A catalogue of dwarf galaxies in the Shapley Supercluster and the role of environment in galaxy nucleation

Abstract Nuclear star clusters (NSCs) are dense star clusters located at the centre of galaxies spanning a wide range of masses and morphologies. Analysing NSC occupation statistics in different environments provides an invaluable window into investigating early conditions of high-density star formation and mass assembly in clusters and group galaxies. We use HST/ACS deep imaging to obtain a catalogue of dwarf galaxies in two galaxy clusters in the Shapley Supercluster: the central cluster Abell 3558 and the northern Abell 1736a. The Shapley region is an ideal laboratory to study nucleation as it stands as the highest mass concentration in the nearby Universe. We investigate the NSC occurrence in quiescent dwarf galaxies as faint as MI = −10 mag and compare it with all other environments where nucleation data is available. We use galaxy cluster/group halo mass as a proxy for the environment and employ a Bayesian logistic regression framework to model the nucleation fraction (fn) as a function of galaxy luminosity and environment. We find a notably high fn in Abell 3558: at MI ≈ −13.1 mag, half the galaxies in the cluster host NSCs. This is higher than in the Virgo and Fornax clusters but comparable to the Coma Cluster. On the other hand, the fn in Abell 1736a is relatively lower, comparable to groups in the Local Volume. We find that the probability of nucleation varies with galaxy luminosity remarkably similarly in galaxy clusters. These results reinforce previous findings of the important role of the environment in NSC formation/growth.

Sardinia Radio Telescope observations of the Coma cluster

ABSTRACT We present deep total intensity and polarization observations of the Coma cluster at 1.4 and 6.6 GHz performed with the Sardinia Radio Telescope. By combining the single-dish 1.4 GHz data with archival Very Large Array observations, we obtain new images of the central radio halo and of the peripheral radio relic where we properly recover the brightness from the large-scale structures. At 6.6 GHz, we detect both the relic and the central part of the halo in total intensity and polarization. These are the highest frequency images available to date for these radio sources in this galaxy cluster. In the halo, we find a localized spot of polarized signal, with fractional polarization of about 45 per cent. The polarized emission possibly extends along the north-east side of the diffuse emission. The relic is highly polarized, up to 55 per cent, as usually found for these sources. We confirm the halo spectrum is curved, in agreement with previous single-dish results. The spectral index is α = 1.48 ± 0.07 at a reference frequency of 1 GHz and varies from α ≃ 1.1, at 0.1 GHz, up to α ≃ 1.8, at 10 GHz. We compare the Coma radio halo surface brightness profile at 1.4 GHz (central brightness and e-folding radius) with the same properties of the other haloes, and we find that it has one of the lowest emissivities observed so far. Reanalysing the relic’s spectrum in the light of the new data, we obtain a refined radio Mach number of M = 2.9 ± 0.1.

Weak-lensing detection of intracluster filaments in the Coma cluster

Weak-lensing detection of intracluster filaments in the Coma cluster

A semi-parametric approach to fitting gas pressure profiles of galaxy clusters

This study focuses on modelling galaxy cluster gas profiles via a semi-parametric nodal approach. While traditional methods like the generalised Navarro–Frenk–White (gNFW) often encounter parameter degeneracy, our flexible node-based method precisely defines a cluster gas pressure profile. Using Planck space telescope data from the Coma region, our model, focused on the pressure-radius relationship, showcases enhanced flexibility over the gNFW. Bayesian analyses indicated an optimal five-node structure for the Coma cluster pressure profile.

Structure and Color Gradients of Ultradiffuse Galaxies in Distant Massive Galaxy Clusters

We have measured structural parameters and radial color profiles of 108 ultradiffuse galaxies (UDGs), carefully selected from six distant massive galaxy clusters in the Hubble Frontier Fields (HFF) in a redshift range from 0.308 to 0.545. Our best-fitting GALFIT models show that the HFF UDGs have a median Sérsic index of 1.09, which is close to 0.86 for local UDGs in the Coma cluster. The median axis-ratio value is 0.68 for HFF UDGs and 0.74 for Coma UDGs, respectively. The structural similarity between HFF and Coma UDGs suggests that they are the same kind of galaxies seen at different times, and that the structures of UDGs do not change at least for several billion years. By checking the distribution of HFF UDGs in the rest-frame UVJ and UVI diagrams, we find a large fraction of them are star forming. Furthermore, a majority of HFF UDGs show small U − V color gradients within the 1 ∗ R e,SMA region, and the fluctuation of the median radial color profile of HFF UDGs is smaller than 0.1 mag, which is compatible to Coma UDGs. Our results indicate that cluster UDGs may fade or quench in a self-similar way, irrespective of the radial distance, in less than ∼4 Gyr.

Fractal Architecture of the Universe Based on Primary-Centric World-View - A Post Copernican Conjecture

This paper investigates the fractal architecture of our Universe based on Primary-Centric Theoretical Formulation. Through theoretical analysis of Earth-Moon System, I arrived at the planetary satellite dynamics which was found to apply equally well to Solar and Exo-solar systems. This gave the theoretical foundation of the New Perspective of the birth and evolution of Exo-solar Systems. This was further extended to the theoretical analysis of star pairs and Neutron-Star pairs. This laid down the Primarycentric World View which I postulate as the physical process which has been shaping the evolution of the Universe and the hot-spots of the Cosmic Microwave Background Radiation right from 380,000 yrs after the Big Bang to date in top-down model resulting into Super-clusters, Clusters, Galaxies and Solar Systems. Primary-centric analysis corresponds to keplerian Analysis for negligibly small mass ratio less than 0.001. In the Copernican Framework, Kepler’s Third Law places no restriction on the orbit of the secondary component in a celestial pair. In Primary Centric Framework there is a very definite constraint on the permitted stable orbit, introduced due to periodic tidal deformations . There are two Clarke’s Orbits which are fully circularized and synchronized and hence nondissipative and equilibrium orbits called inner and outer Clarke's orbits equivalent to two geosynchronous orbits in Earth-Moon scenario. Outer Clarke’s Orbit is permissible as a stable orbit if the mass ratio of secondary to primary is greater than 0.2, Inner Clarke’s Orbit is permissible if mass ratio is less than 10-4 . If the mass ratio is between 10-4 to 0.2 then secondary spirals-out from inner Clarke’s Orbit to outer Clarke’s Orbit if it tumbles into super-synchronous orbit and spirals-in if it tumbles into sub-synchronous orbit destined to be destroyed by the primary. My conjecture states that every cosmological sub-system has a Monarch (or dominant) Primary (M_primary) Component anchoring the given sub-system and this Primary decides the stable equilibrium orbits of the secondary/secondaries. Planet-Satellite has a Planet as the M_primary, Solar System and exo-Solar Systems have a planet hosting star (PHS) as the M_primary, Galaxy has a Super-Massive Black Hole(SMBH) as the M_primary, Cluster has a cD galaxy (central dominant Galaxy) which is also known as Brightest Cluster Galaxy(BCG) as the M_primary, Super-Cluster has a massive Cluster hosting a QUASER/Blazer as the M_primary. This goes adinfinitum until a Cosmic Web is woven with Cosmic filaments. This conjecture gains a definite credence after the recent discoveries of the over-massive Black Holes in M_Galaxies namely Messier 87 in Virgo Cluster, NGC 3842 in Leo Cluster, NGC 4889 in Coma Cluster[68] and NGC 1277 in Perseus Cluster[66] which had been proposed as M_Galaxies on general considerations even before the confirmation of over-massive black holes. In 2011, a group of floating planets have been discovered. This is a transitory event and is an exception to this conjecture.

THE STUDY OF X-RAY SPECTRUM OF COMA GALAXY CLUSTER

The X-ray spectrum of the Coma galaxy cluster was studied using the data from the XMM-Newton observatory. We combined 7 observations performed with the MOS camera of XMM-Newton in the 40′ × 40′ region centered at the Coma cluster. The analyzed observations were performed in 2000–2005 and have a total duration of 196 ksec. We focus on the analysis of the MOS camera spectra due to their lower affection by strong instrumental line-like background. The obtained spectrum was fitted with a model including contributions from the Solar system/Milky Way hot plasma and a power law X-ray background. The contribution of the instrumental background was modeled as a power law (not convolved with the effective area) and a number of Gaussian lines. The contribution from the Coma cluster was modeled with a single-temperature hot plasma emission. In addition, we searched for possible non-thermal radiation present in the vicinity of the center of the Coma cluster, originating e.g. from synchrotron emission of relativistic electrons on a turbulent magnetic field. We compared the results with previous works by other authors and spectra obtained from other instruments that operate in the similar energy range of 1−10 keV. Careful and detailed spectrum analysis shall be a necessary contribution to our future work – searching for axion-like dark matter particles’ manifestations in the Coma cluster.

A giant thin stellar stream in the Coma Galaxy Cluster

The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream (μg, max = 29.5 mag arcsec−2) with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects are found ahead of their promising future application in the study of the properties of dark matter.

Constraining Baryon Loading Efficiency of Active Galactic Nuclei with Diffuse Neutrino Flux from Galaxy Clusters

Active galactic nuclei (AGNs) are widely believed to be one of the promising acceleration sites of ultrahigh-energy cosmic rays (CRs). Essentially, AGNs are powered by the gravitational energy of matter falling into supermassive black holes. However, the conversion efficiency of gravitational to kinetic energy of CRs in AGNs, which is defined as the baryon loading factor η p , is not well known yet. After being accelerated, high-energy CRs could escape the host galaxy and enter the intracluster medium (ICM). These CRs can be confined within the galaxy cluster and produce γ-rays and neutrinos through proton–proton collisions with the ICM. In this paper, we study the diffusion of CRs in galaxy clusters and calculate the diffuse neutrino flux from the galaxy cluster population. Using the latest upper limits on the cumulative unresolved TeV–PeV neutrino flux from galaxy clusters posed by the IceCube Neutrino Observatory, we derive the upper limit of the average baryon loading factor as η p,grav ≲ 2 × 10−3 − 0.1 for the population of galaxy clusters. This constraint is more stringent than the one obtained from γ-ray observation on the Coma cluster.

Initial mass function variability from the integrated light of diverse stellar systems

ABSTRACT We present a uniform analysis of the stellar initial mass function (IMF) from integrated light spectroscopy of 15 compact stellar systems (11 globular clusters in M31 and 4 ultra compact dwarfs in the Virgo cluster, UCDs) and two brightest Coma cluster galaxies (BCGs), covering a wide range of metallicities (−1.7 &amp;lt; [Fe/H] &amp;lt; 0.01) and velocity dispersions (7.4 km s−1 &amp;lt;σ &amp;lt; 275 km s−1). The S/N ∼100 Å−1 Keck LRIS spectra are fitted over the range 4000 &amp;lt; λ/Å &amp;lt; 10 000 with flexible full-spectrum stellar population synthesis models. We use the models to fit simultaneously for ages, metallicities, and individual elemental abundances of the population, allowing us to decouple abundance variations from variations in IMF slope. We show that compact stellar systems do not follow the same trends with physical parameters that have been found for early-type galaxies. Most globular clusters in our sample have an IMF consistent with that of the Milky Way, over a wide range of [Fe/H] and [Mg/Fe]. There is more diversity among the UCDs, with some showing evidence for a bottom-heavy IMF, but with no clear correlation with metallicity, abundance, or velocity dispersion. The two Coma BCGs have similar velocity dispersion and metallicity, but we find the IMF of NGC 4874 is consistent with that of the Milky Way while NGC 4889 presents evidence for a significantly bottom-heavy IMF. For this sample, the IMF appears to vary between objects in a way that is not explained by a single metallicity-dependent prescription.