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II Zw 40 is a starburst dwarf and merger product, and holds a radio-infrared supernebula excited by thousands of embedded OB stars. We present here observations of three aspects of the supernebula: maps of the K and KU radio continuum that trace dense ionized gas with spatial resolution |${\sim} 0.1^{\prime \prime }$|⁠ , a spectral data cube of the [S  iv ] |$10.5\,\mu$| m emission line that measures the kinematics of the ionized gas with velocity resolution 4.5 km s |$^{-1}$|⁠ , and an ALMA (Atacama Large Millimeter Array) spectral cube of the CO(3-2) line that probes the dense warm molecular gas with spatial and velocity resolution comparable to the ionized gas. The observations suggest that the supernebula is the overlap, collision or merger of two star clusters, each associated with an elongated molecular cloud. We accordingly modelled the supernebula with simulations of colliding clusters. The model that best agrees with the data is a grazing collision that has distorted the gas and stars to create the distinctive structures observed. These models may have wide applicability in the cluster-rich regions of young starbursts. [ABSTRACT FROM AUTHOR]

By the end of the next decade, we hope to have detected strongly lensed gravitational waves by galaxies or clusters. Although there exist optimal methods for identifying lensed signal, it is shown that machine learning (ML) algorithms can give comparable performance but are orders of magnitude faster than non-ML methods. We present the SLICK pipeline which comprises a parallel network based on deep learning. We analyse the Q-transform maps (QT maps) and the Sine-Gaussian projection (SGP) maps generated for the binary black hole signals injected in Gaussian as well as real noise. We compare our network performance with the previous work and find that the efficiency of our model is higher by a factor of 5 at a false positive rate of 0.001. Further, we show that including SGP maps with QT maps data result in a better performance than analysing QT maps alone. When combined with sky localization constraints, we hope to get unprecedented accuracy in the predictions than previously possible. We also evaluate our model on the real events detected by the LIGO–Virgo collaboration and find that, at a threshold of 0.75 our network correctly classifies all of them, consistent with non-detection of lensing. [ABSTRACT FROM AUTHOR]

To investigate how the radio-identified active galactic nuclei (AGN) fraction varies with cluster-centric radius, we present the projected and de-projected distributions of a large sample of Low-Frequency Array-identified radio AGN out to |$30R_{500}$| around galaxy clusters. The AGN fraction experiences a |${\sim} 25~{{\ \rm per\ cent}}$| increase above the field fraction in the cluster outskirts at around |$10R_{500}$|⁠ , a |${\sim} 20~{{\ \rm per\ cent}}$| decrease around |${\sim} 0.5R_{500}$|⁠ , and an increase of over three times the field fraction value in the very cluster core. We label these three radial windows the outer, intermediate , and inner regions respectively, and investigate how these radial trends might arise due to intrinsic properties of the AGN population. The only difference seen in host galaxy stellar mass is in the inner region, where there is a much higher fraction of massive host galaxies. Analysing AGN radio luminosity, regions with a higher AGN fraction tend to have more radio luminous AGN, and vice versa. We discuss the physical mechanisms that might be responsible for these results with reference to the literature. [ABSTRACT FROM AUTHOR]

In a recent series of papers, supermassive black holes were used to discern pathways in galaxy evolution. By considering the black holes' coupling with their host galaxy's bulge/spheroid, the progression of mass within each component has shed light on the chronological sequence of galaxy speciation. Offsets between the galaxy-morphology-dependent |$M_{\rm bh}$| – |$M_{\rm \star ,sph}$| scaling relations trace a pattern of 'punctuated equilibrium' arising from merger-driven transitions between galaxy types, such as from spirals to dust-rich lenticulars and further to 'ellicular' and elliptical galaxies. This study delves deeper into the distinction between the ellicular galaxies – characterised by their intermediate-scale discs – and elliptical galaxies. Along the way, it is shown how some antitruncated large-scale discs in lenticular galaxies can arise from the coexistence of a steep intermediate-scale disc and a relatively shallow large-scale disc. This observation undermines application of the popular exponential-disc plus Sérsic-bulge model for lenticular galaxies and suggests some past bulge mass measurements have been overestimated. Furthermore, it is discussed how merger-driven disc-heating and blending likely leads to the spheroidalisation of discs and the conglomeration of multiple discs leads to the (high- n) Sérsicification of light profiles. The ellicular and elliptical galaxy distribution in the |$M_{\rm bh}$| – |$M_{\rm \star ,sph}$| diagram is explored relative to major-merger-built lenticular galaxies and brightest cluster galaxies. The super-quadratic |$M_{\rm bh}$| – |$M_{\rm \star }$| relations, presented herein, for merger-built systems should aid studies of massive black hole collisions and the gravitational wave background. Finally, connections to dwarf compact elliptical and ultracompact dwarf galaxies, with their 100–1000 times higher |$M_{\rm bh}/M_{\rm \star ,sph}$| ratios, are presented. [ABSTRACT FROM AUTHOR]

The impact of viscosity in the intracluster medium (ICM) is still an open question in astrophysics. To address this problem, we have run a set of cosmological simulations of three galaxy clusters with a mass larger than M Vir > 1015 M ⊙ at z = 0 using the smoothed particle magnetohydrodynamics-code OpenGadget3. We aim to quantify the influence of viscosity and constrain its value in the ICM. Our results show significant morphological differences at small scales, temperature variations, and density fluctuations induced by viscosity. We observe a suppression of instabilities at small scales, resulting in a more filamentary structure and a larger amount of small structures due to the lack of mixing with the medium. The conversion of kinetic to internal energy leads to an increase of the virial temperature of the cluster of ∼5%–10%, while the denser regions remain cold. The amplitude of density and velocity fluctuations are found to increase with viscosity. However, comparison with observational data indicates that the simulations, regardless of the viscosity, match the observed slope of the amplitude of density fluctuations, challenging the direct constraint of viscosity solely through density fluctuations. Furthermore, the ratio of density to velocity fluctuations remains close to 1 regardless of the amount of viscosity, in agreement with the theoretical expectations. Our results show for the first time in a cosmological simulation of a galaxy cluster the effect of viscosity in the ICM, a study that is currently missing in the literature. [ABSTRACT FROM AUTHOR]

We present the first multifrequency analysis of the candidate ultrasteep spectrum radio halo in the galaxy cluster PLCKESZ G171.94−40.65, using the upgraded Giant Metrewave Radio telescope (400 MHz), and Karl G. Jansky Very Large Array (1–2 GHz) observations. Our radio data have been complemented with archival Chandra X-ray observations to provide a crucial insight into the complex intracluster medium physics, happening at large scales. We detect the radio halo emission to the extent of ∼1.5 Mpc at 400 MHz, significantly larger than previously reported, along with five tailed galaxies in the central region. We also report the discovery of an unknown diffuse source "U," at the cluster periphery, with an extent of 300 kpc. Using the available observations, we have found that the radio spectrum of the halo is well-fitted with a single power law, having a spectral index of −1.36 ± 0.05, indicating that it is not an ultrasteep spectrum radio halo. Our low-resolution (25″) resolved spectral map shows an overall uniform spectral index, with some patches of fluctuations. The X-ray and radio surface brightness are morphologically cospatial, with a slight extension along the northwest–southeast direction, seen in both maps. The radio and X-ray surface brightness indicates strong positive correlations, with sublinear correlation slopes (∼0.71). Multiple tailed galaxies and the radio halo indicate a high dynamical activity at the cluster central region. [ABSTRACT FROM AUTHOR]

JKCS041 (⁠|$z=1.8$|⁠) is one of the most distant galaxy cluster systems known, seen when the Universe was less than 4 billion years old. Recent Sunyaev–Zeldovich (SZ) observations show a temperature decrement that is less than expected based on mass estimates of the system from X-ray, weak gravitational lensing, and galaxy richness measurements. In this paper, we seek to explain the observables – in particular the low SZ decrement and single SZ peak, the projected offset between the X-ray and SZ peaks of |$\approx$| 220 kpc, the gas mass measurements and the lensing mass estimate. We use the gamer-2 hydrodynamic code to carry out idealized numerical simulations of cluster mergers and compare resulting synthetic maps with the observational data. Generically, a merger process is necessary to reproduce the observed offset between the SZ and X-ray peaks. From our exploration of parameter space, seen a few tenths of a Gyr after first core passage, two components with total mass of |$\approx 2\times 10^{14} \,\text{M}_\odot$|⁠ , mass ratio of |$\approx$| 2:3, gas fraction of |$0.05-0.1$|⁠ , and Navarro, Frenk and White mass density profile concentrations c |$\approx$| 5 are scenarios that are consistent with the observational data. For consistency with the SZ and X-ray measurements, our simulations exclude total mass in excess of |$\approx 3\times 10^{14} {\rm M}_{\odot }$|⁠ , primarily based on the SZ signal. The mass ratio is constrained by the SZ–X-ray offset and magnitude of the SZ signal, ruling out systems with equal and vastly different masses. [ABSTRACT FROM AUTHOR]

Recent observations from the EIGER JWST program have measured for the first time the quasar–galaxy cross-correlation function at |$z\approx 6$|⁠. The autocorrelation function of faint |$z\approx 6$| quasars was also recently estimated. These measurements provide key insights into the properties of quasars and galaxies at high redshift and their relation with the host dark matter haloes. In this work, we interpret these data building upon an empirical quasar population model that has been applied successfully to quasar clustering and demographic measurements at |$z\approx 2\!-\!4$|⁠. We use a new, large-volume N -body simulation with more than a trillion particles, FLAMINGO-10k, to model quasars and galaxies simultaneously. We successfully reproduce observations of |$z\approx 6$| quasars and galaxies (i.e. their clustering properties and luminosity functions), and infer key quantities such as their luminosity–halo mass relation, the mass function of their host haloes, and their duty cycle/occupation fraction. Our key findings are (i) quasars reside on average in |$\approx 10^{12.5}\, {\rm M}_{\odot }$| haloes (corresponding to |$\approx 5\sigma$| fluctuations in the initial conditions of the linear density field), but the distribution of host halo masses is quite broad; (ii) the duty cycle of (UV-bright) quasar activity is relatively low (⁠|$\approx 1~{{\ \rm per\ cent}}$|⁠); (iii) galaxies (that are bright in [O  iii ]) live in much smaller haloes (⁠|$\approx 10^{10.9}\, {\rm M}_{\odot }$|⁠) and have a larger duty cycle (occupation fraction) of |$\approx 13~{{\ \rm per\ cent}}$|⁠. Finally, we focus on the inferred properties of quasars and present a homogeneous analysis of their evolution with redshift. The picture that emerges reveals a strong evolution of the host halo mass and duty cycle of quasars at |$z\approx 2\!-\!6$|⁠ , and calls for new investigations of the role of quasar activity across cosmic time. [ABSTRACT FROM AUTHOR]

We explore correlations between the orientations of small galaxy groups, or 'multiplets', and the large-scale gravitational tidal field. Using data from the Dark Energy Spectroscopic Instrument (DESI) Y1 survey, we detect the intrinsic alignment (IA) of multiplets to the galaxy-traced matter field out to separations of |$100\,h^{-1}$|  Mpc. Unlike traditional IA measurements of individual galaxies, this estimator is not limited by imaging of galaxy shapes and allows for direct IA detection beyond redshift |$z=1$|⁠. Multiplet alignment is a form of higher order clustering, for which the scale-dependence traces the underlying tidal field and amplitude is a result of small-scale (⁠|$\lt 1h^{-1}$|  Mpc) dynamics. Within samples of bright galaxies, luminous red galaxies (LRG) and emission-line galaxies, we find similar scale-dependence regardless of intrinsic luminosity or colour. This is promising for measuring tidal alignment in galaxy samples that typically display no IA. DESI's LRG mock galaxy catalogues created from the A  bacus S  ummit N -body simulations produce a similar alignment signal, though with a 33 per cent lower amplitude at all scales. An analytic model using a non-linear power spectrum (NLA) only matches the signal down to 20  |$h^{-1}$|  Mpc. Our detection demonstrates that galaxy clustering in the non-linear regime of structure formation preserves an interpretable memory of the large-scale tidal field. Multiplet alignment complements traditional two-point measurements by retaining directional information imprinted by tidal forces, and contains additional line-of-sight information compared to weak lensing. This is a more effective estimator than the alignment of individual galaxies in dense, blue, or faint galaxy samples. [ABSTRACT FROM AUTHOR]

We present an in-depth investigation of galaxy clustering based on a new suite of realistic large-box galaxy formation simulations in |$f(R)$| gravity, with a subgrid physics model that has been recalibrated to reproduce various observed stellar and gas properties. We focus on the two-point correlation functions of the luminous red galaxies (LRGs) and emission line galaxies (ELGs), which are primary targets of ongoing and future galaxy surveys such as Dark Energy Spectroscopic Instrument (DESI). One surprising result is that, due to several non-trivial effects of modified gravity on matter clustering and the galaxy–halo connection, the clustering signal does not depend monotonically on the fifth-force strength. For LRGs, this complicated behaviour poses a challenge to meaningfully constraining this model. For ELGs, in contrast, this can be straightforwardly explained by the time evolution of the fifth force, which means that weaker |$f(R)$| models can display nearly the same – up to 25 per cent – deviations from Lambda cold dark matter model as the strongest ones, albeit at lower redshifts. This implies that even very weak |$f(R)$| models can be strongly constrained, unlike with most other observations. Our results show that galaxy formation acquires a significant environment dependence in |$f(R)$| gravity, which, if not properly accounted for, may lead to biased constraints on the model. This highlights the essential role of hydrodynamical simulations in future tests of gravity exploring precision galaxy-clustering data from the likes of DESI and Euclid. [ABSTRACT FROM AUTHOR]

Galaxy clusters provide an avenue to expand our knowledge of cosmology and galaxy evolution. Because it is difficult to accurately measure the total mass of a large number of individual clusters, cluster samples are typically selected using an observable proxy for mass. Selection effects are therefore a key problem in understanding galaxy cluster statistics. We make use of the |$(2.8~\rm {Gpc})^3$| FLAMINGO hydrodynamical simulation to investigate how selection based on X-ray luminosity, thermal Sunyaev–Zeldovich effect or galaxy richness influences the halo mass distribution. We define our selection cuts based on the median value of the observable at a fixed mass and compare the resulting samples to a mass-selected sample. We find that all samples are skewed towards lower mass haloes. For X-ray luminosity and richness cuts below a critical value, scatter dominates over the trend with mass and the median mass becomes biased increasingly low with respect to a mass-selected sample. At |$z\le 0.5$|⁠ , observable cuts corresponding to median halo masses between |$M_\text{500c}=10^{14}$| and |$10^{15}~\rm {{\rm M}_{\odot }}$| give nearly unbiased median masses for all selection methods, but X-ray selection results in biased medians for higher masses. For cuts corresponding to median masses |$\lt 10^{14}$| at |$z\le 0.5$| and for all masses at |$z\ge 1$|⁠ , only Compton-Y selection yields nearly unbiased median masses. Importantly, even when the median mass is unbiased, the scatter is not because for each selection the sample is skewed towards lower masses than a mass-selected sample. Each selection leads to a different bias in secondary quantities like cool-core fraction, temperature, and gas fraction. [ABSTRACT FROM AUTHOR]

Understanding faint dwarf galaxies is fundamental to the development of a robust theory of galaxy formation on small scales. Since the discovery of a population of ultra diffuse galaxies (UDGs) rich in globular clusters (GCs) in Coma, an increasing number of studies on low surface brightness dwarf galaxies (LSBds) have been published in recent years. The most massive LSBds have been observed predominantly in groups and clusters, with properties displaying dependence on the environment. In this work, we use deep DECam imaging to systematically identify LSBds and their GC populations around the low-density environment of NGC 3115. We carefully analyse the structure and morphology of 24 candidates, 18 of which are reported for the first time. Most candidates exhibit red colours suggesting a connection between their colour and distance to NGC 3115. We followed up with Gemini GMOS imaging 9 LSBds to properly identify their GC populations. We derive lower limits for the number of GCs associated with each galaxy. Our analysis reveals that they occur around of the same loci of Fornax LSB dwarf GC systems. The relationship between the number of GCs and total mass provides a tool in which, by counting the GCs in these galaxies, we estimate an upper limit for the total mass of these LSB dwarfs, obtaining the mean value of |$\sim 3.3\times 10^{10}$|  M |$_{\odot }$|⁠. Our results align with expectations for dwarf-sized galaxies, particularly regarding the distribution and specific frequency of their GC systems. [ABSTRACT FROM AUTHOR]

In this paper, we calculate the energy, signal-to-noise ratio (SNR), detection range, and angular anisotropy of the matter, matter memory, and neutrino memory gravitational-wave (GW) signatures of 21 three-dimensional initially nonrotating core-collapse supernova (CCSN) models carried to late times. We find that inferred energy, SNR, and detection range are angle-dependent quantities, and that the spread of possible energy, signal to noise, and detection ranges across all viewing angles generally increases with progenitor mass. When examining the low-frequency matter memory and neutrino memory components of the signal, we find that the neutrino memory is the most detectable component of a CCSN GW signal, and that DECIGO is best equipped to detect both matter memory and neutrino memory. Moreover, we find that the polarization angle between the h + and h × strains serves as a unique identifier of matter and neutrino memory. Finally, we develop a Galactic density- and stellar mass-weighted formalism to calculate the rate at which we can expect to detect CCSN GW signals with the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO). When considering only the matter component of the signal, the aLIGO detection rate is around 65% of the total Galactic supernova rate, but increases to 90% when incorporating the neutrino memory component. We find that all future detectors (Einstein Telescope, Cosmic Explorer, DECIGO) will be able to detect CCSN GW signals from the entire Galaxy, and for the higher-mass progenitors even into the Local Group of galaxies. [ABSTRACT FROM AUTHOR]

Relic galaxies, the oldest ultra-compact massive galaxies (UCMGs), contain almost exclusively 'pristine' stars formed during an intense star formation (SF) burst at high redshift. As such, they allow us to study in detail the early mechanism of galaxy assembly in the Universe. Using the largest catalogue of spectroscopically confirmed UCMGs for which a degree of relicness (DoR) had been estimated, the INSPIRE catalogue, we investigate whether or not relics prefer dense environments. The objective of this study is to determine if the DoR, which measures how extreme the SF history was, and the surrounding environment are correlated. In order to achieve this goal, we employ the AMICO galaxy cluster catalogue to compute the probability for a galaxy to be a member of a cluster, and measure the local density around each UCMG using machine learning-based photometric redshifts. We find that UCMGs can reside both in clusters and in the field, but objects with very low DoR (⁠|$\lt 0.3$|⁠ , i.e. a relatively extended SF history) prefer underdense environments. We additionally report a correlation between the DoR and the distance from the cluster centre: more extreme relics, when located in clusters, tend to occupy the more central regions of them. We finally outline potential evolution scenarios for UCMGs at different DoR to reconcile their presence in both clusters and field environments. [ABSTRACT FROM AUTHOR]

Galaxy groups contain the majority of bound mass with a significant portion of baryons due to the combination of halo mass and abundance (Cui 2024). Hence they serve as a crucial missing piece in the puzzle of galaxy formation and the evolution of large-scale structures in the Universe. In observations, mass-complete group catalogues are normally derived from galaxy redshift surveys detected through various three-dimensional group-finding algorithms. Confirming the reality of such groups, particularly in the X-rays, is critical for ensuring robust studies of galaxy evolution in these environments. Recent works have reported numerous optical groups that are X-ray undetected (see, e.g. Popesso et al. 2024), sparking debates regarding the reasons for the unexpectedly low hot gas fraction in galaxy groups. To address this issue, we utilize zoomed-in simulations of galaxy groups from the novel Hyenas project to explore the range of hot gas fractions within galaxy groups and investigate the intrinsic factors behind the observed variability in X-ray emission. We find that the halo formation time can play a critical role–we see that groups in haloes that formed earlier exhibit up to an order of magnitude brighter X-ray luminosities compared to those formed later. This suggests that undetected X-ray groups are preferentially late-formed haloes and highlights the connection between gas fraction and halo formation time in galaxy groups. Accounting for these biases in galaxy group identification is essential for advancing our understanding of galaxy formation and achieving precision in cosmological studies. [ABSTRACT FROM AUTHOR]

We present photometric redshifts (photo- z) for the deep wide fields of the Physics of the Accelerating Universe Survey (PAUS), covering an area of |$\sim$| 50 deg |$^{2}$|⁠ , for |$\sim$| 1.8 million objects up to |$i_{\rm {AB}}\lt 23$|⁠. The PAUS deep wide fields overlap with the W1 and W3 fields from CFHTLenS and the G09 field from KiDS/GAMA. Photo- z are estimated using the 40 narrow bands (NB) of PAUS and the broad-bands (BB) of CFHTLenS and KiDS. We compute the redshifts with the SED template-fitting code bcnz , with a modification in the calibration technique of the zero-point between the observed and the modelled fluxes, that removes any dependence on spectroscopic redshift samples. We enhance the redshift accuracy by introducing an additional photo- z estimate (⁠|$z_{\textrm {b}}$|⁠), obtained through the combination of the bcnz and the BB-only photo- z. Comparing with spectroscopic redshift estimates (⁠|$z_{\textrm {s}}$|⁠), we obtain a |$\sigma _{68} \simeq 0.020$| for all galaxies with |$i_{\rm {AB}}\lt 23$| and a typical bias |$|z_{\textrm {b}}\!-\!z_{\textrm {s}}|$| smaller than 0.01. For |$z_{\textrm {b}} \sim (0.10\!-\!0.75)$|⁠ , we find |$\sigma _{68} \simeq (0.003\!-\!0.02)$|⁠ , this is a factor of |$10\!-\!2$| higher accuracy than the corresponding BB-only results. We obtain similar performance when we split the samples into red (passive) and blue (active) galaxies. We validate the redshift probability |$p(z)$| obtained by bcnz and compare its performance with that of |$z_{\textrm {b}}$|⁠. These photo- z catalogues will facilitate important science cases, such as the study of galaxy clustering and intrinsic alignment at high redshifts (⁠|$z \lesssim 1$|⁠) and faint magnitudes. [ABSTRACT FROM AUTHOR]

Unlike in 4k dimensions, the action of charge conjugation operator in 4k + 2 dimensions preserves spinor chirality. This property, in a generic orbifolded geometry (of scale 1 / R ∼ O (1 TeV)) with KK number conservation, leads to baryon number violating operators with KK fermion modes. These exotic operators can be mapped on to the 4D operators responsible for proton decay and hydrogen–antihydrogen oscillation by introducing the KK-1 hypercharge gauge boson interaction. This KK-1 hypercharge gauge boson, being the lightest, is stable and is the ideal dark matter (DM) candidate in the model. Hence, dark matter becomes a crucial ingredient in facilitating the proton decay and Δ B = 2 = Δ L processes. Thus, this model answeres the lack of their evidence in terrestrial experiments owing to the low density of dark matter on Earth. Nevertheless, though terrestrial experiments are not yet sensitive to dark matter influenced baryon number violations, their rates can be substantially enhanced in dense DM clusters at the centre of galaxies. [ABSTRACT FROM AUTHOR]

We introduce a GPU-accelerated hybrid hydro/ N -body code (Enzo-N) designed to address the challenges of concurrently simulating star clusters and their parent galaxies. This task has been exceedingly challenging, primarily due to the considerable computational time required, which stems from the substantial scale difference between galaxies (∼0.1 Mpc) and star clusters (∼parsecs). Yet, this significant scale separation means that particles within star clusters perceive those outside the star cluster in a semistationary state. By leveraging this aspect, we integrate a direct N -body code (Nbody6++GPU) into a cosmological (magneto)hydrodynamic code (Enzo) through utilization of the semistationary background acceleration approximation. We solve the dynamics of particles within star clusters using a direct N -body solver with regularization for few-body interactions, while evolving particles outside—dark matter, gas, and stars—using a particle-mesh gravity solver and hydrodynamic methods. We demonstrate that Enzo-N successfully simulates the coevolution of star clusters and their parent galaxies, capturing phenomena such as core collapse of the star cluster and tidal stripping due to galactic tides. This comprehensive framework opens up new possibilities for studying the evolution of star clusters within galaxies, offering insights that were previously inaccessible. [ABSTRACT FROM AUTHOR]

Mergers of and interactions between galaxies imprint a wide diversity of morphological, dynamical, and chemical characteristics in stellar halos and tidal streams. Measuring these characteristics elucidates aspects of the progenitors of the galaxies we observe today. The M81 group is the perfect galaxy group to understand the past, present, and future of a group of galaxies in the process of merging. Here, we measure the end of star formation (t 90) and metallicity ([M/H]) of the stellar halo of M82 and the eastern tidal stream of NGC 3077 to: (1) test the idea that M82 possesses a genuine stellar halo, formed before any interaction with M81; (2) determine if NGC 3077's tidal disruption is related to the star formation history in its tails; and (3) create a timeline of the assembly history of the central trio in the M81 group. We argue that M82 possesses a genuine, metal-poor ([M/H] ∼ −1.62 dex) stellar halo, formed from the merger of a small satellite galaxy roughly 6.6 Gyr ago. We also find that the stars present in NGC 3077's tails formed before tidal disruption with M81, and possess a roughly uniform metallicity as shown in S. Okamoto et al., implying that NGC 3077's progenitor had significant population gradients. Finally, we present a timeline of the central trio's merger/interaction history. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive overview of how fitting of baryon acoustic oscillations (BAO) is carried out within the upcoming Dark Energy Spectroscopic Instrument's (DESI) 2024 results using its DR1 data set, and the associated systematic error budget from theory and modelling of the BAO. We derive new results showing how non-linearities in the clustering of galaxies can cause potential biases in measurements of the isotropic (⁠|$\alpha _{\mathrm{iso}}$|⁠) and anisotropic (⁠|$\alpha _{\mathrm{ap}}$|⁠) BAO distance scales, and how these can be effectively removed with an appropriate choice of reconstruction algorithm. We then demonstrate how theory leads to a clear choice for how to model the BAO and develop, implement, and validate a new model for the remaining smooth-broad-band (i.e. without BAO) component of the galaxy clustering. Finally, we explore the impact of all remaining modelling choices on the BAO constraints from DESI using a suite of high-precision simulations, arriving at a set of best practices for DESI BAO fits, and an associated theory and modelling systematic error. Overall, our results demonstrate the remarkable robustness of the BAO to all our modelling choices and motivate a combined theory and modelling systematic error contribution to the post-reconstruction DESI BAO measurements of no more than 0.1 per cent (0.2 per cent) for its isotropic (anisotropic) distance measurements. We expect the theory and best practices laid out to here to be applicable to other BAO experiments in the era of DESI and beyond. [ABSTRACT FROM AUTHOR]

The diffuse stellar component of galaxy clusters made up of intergalactic stars is termed the intracluster light (ICL). Although there is a developing understanding of the mechanisms by which the ICL is formed, no strong consensus has yet been reached on which objects the stars of the ICL are primarily sourced from. We investigate the assembly of the ICL starting approximately 10 Gyr before |$z=0$| in 11 galaxy clusters (halo masses between |$\sim 1\times 10^{14}$| and |$\sim 7\times 10^{14}$|  M |$_{\odot }$| at |$z\approx 0$|⁠) in the Horizon-AGN simulation. By tracking the stars of galaxies that fall into these clusters past cluster infall, we are able to link almost all of the |$z\approx 0$| ICL back to progenitor objects. Satellite stripping, mergers, and pre-processing are all found to make significant contributions to the ICL, but any contribution from in situ star formation directly into the ICL appears negligible. Even after compensating for resolution effects, we find that approximately 90 per cent of the stacked ICL of the 11 clusters that is not pre-processed should come from galaxies infalling with stellar masses above |$10^{9}$|  M |$_{\odot }$|⁠ , with roughly half coming from infalling galaxies with stellar masses within half a dex of |$10^{11}$|  M |$_{\odot }$|⁠. The fact that the ICL appears largely sourced from such massive objects suggests that the ICL assembly of any individual cluster may be principally stochastic. [ABSTRACT FROM AUTHOR]

The overall objective of this study is to investigate claims found in the literature that fossil groups, characterized by a large magnitude gap between their two brightest galaxies, are darker, i.e. exhibit higher mass-to-light (M/L) ratios, compared to regular groups. Specifically, we aim to measure the mass of these systems using the weak gravitational lensing technique. To achieve this, we obtained deep images of four fossil systems with the CFHT telescope in the |$r$| and g bands. Through a careful process of weak gravitational shear measurement, including corrections for the point spread function (PSF) and contamination from group and foreground galaxies, we fit NFW models and obtained mass measurements as a result. Similarly, we quantified the light distribution produced by these groups, taking into account relevant data gaps in the images due to the presence of bright stars, as well as contamination from foreground and background galaxies. We obtained masses and M/L ratios that are consistent with previous results where mass was estimated from galaxy dynamics. Indeed, the four fossil systems studied here exhibit high M/L ratios compared to the general population of systems. Drawing more generalizable conclusions from a sample of only four systems is challenging. However, the procedure outlined in this study can be applied to large image surveys, allowing for a revisiting of this question with significantly reduced statistical uncertainties. This will enable a more homogeneous comparison between fossil groups and clusters and the overall population. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper we introduce the galaxy of Coxeter groups (of finite rank) – an infinite dimensional, locally finite, ranked simplicial complex which captures isomorphisms between finite rank Coxeter systems. In doing so, we would like to suggest a new framework to study the isomorphism problem for Coxeter groups. We prove some structural results about this space, provide a full characterization in small ranks and propose many questions. In addition we survey known tools, results and conjectures. Along the way we show profinite rigidity of triangle Coxeter groups – a result which is possibly of independent interest. [ABSTRACT FROM AUTHOR]

Subhalo dynamics in galaxy cluster host halos govern the observed distribution and properties of cluster member galaxies. We use the IllustrisTNG simulation to investigate the accretion and orbits of subhalos found in cluster-size halos. We find that the median change in the major axis direction of cluster-size host halos is approximately 80° between a ∼ 0.1 and the present day. We identify coherent regions in the angular distribution of subhalo accretion, and ∼68% of accreted subhalos enter their host halo through ∼38% of the surface area at the virial radius. The majority of galaxy clusters in the sample have ∼2 such coherent regions. We further measure angular orbits of subhalos with respect to the host major axis and use a clustering algorithm to identify distinct orbit modes with varying oscillation timescales. The orbit modes correlate with subhalo accretion conditions. Subhalos in orbit modes with shorter oscillations tend to have lower peak masses and accretion directions somewhat more aligned with the major axis. One orbit mode, exhibiting the least oscillatory behavior, largely consists of subhalos that accrete near the plane perpendicular to the host halo major axis. Our findings are consistent with expectations from inflow from major filament structures and internal dynamical friction: most subhalos accrete through coherent regions, and more massive subhalos experience fewer orbits after accretion. Our work offers a unique quantification of subhalo dynamics that can be connected to how the intracluster medium strips and quenches cluster galaxies. [ABSTRACT FROM AUTHOR]

Several large JWST blank field observing programs have not yet discovered the first galaxies expected to form at 15 ≤ z ≤ 20. This has motivated the search for more effective survey strategies that will be able to effectively probe this redshift range. Here, we explore the use of gravitationally lensed cluster fields, which have historically been the most effective discovery tool with the Hubble Space Telescope. In this paper, we analyze the effectiveness of the most massive galaxy clusters that provide the highest median magnification factor within a single JWST NIRCam module in uncovering this population. The results of exploiting these lensing clusters to break the z > 15 barrier are compared against the results from large-area, blank-field surveys such as JADES and CEERS in order to determine the most effective survey strategy for JWST. We report that the fields containing massive foreground galaxy clusters specifically chosen to occupy the largest fraction of a single NIRCam module with high magnification factors in the source plane while containing all multiple images in the image plane within a single module provide the highest probability of both probing the 15 ≤ z ≤ 20 regime as well as discovering the highest-redshift galaxy possible with JWST. We also find that using multiple massive clusters in exchange for shallower survey depths is a more time-efficient method of probing the z > 15 regime. [ABSTRACT FROM AUTHOR]

The consequences of a 90° barrier in the scattering of energetic electrons by whistler waves are explored with self-consistent two-dimensional particle-in-cell simulations. In the presence of a 90° scattering barrier, a field-aligned heat flux of energetic electrons will rapidly scatter to form a uniform distribution with pitch angles 0 < θ < 90 ° but with a discontinuous jump at θ = 90 ° to a lower energy distribution of electrons with 90 ° < θ < 180 °. However, simulations reveal that such a distribution contains a large reservoir of free energy that is released to drive large-amplitude, oblique-propagating whistler waves (δ B / B 0 ∼ 0.1). As a result, energetic electrons near a pitch angle 90° experience strong resonance scattering. Nearly half of the energetic electrons in the positive parallel velocity plane cross the 90° barrier and diffuse to negative parallel velocities. Thus, the late-time electron velocity distribution becomes nearly isotropic. This result has implications for understanding the regulation of energetic particle heat flux in space and astrophysical environments, including the solar corona, the solar wind, and the intracluster medium of galaxy clusters. [ABSTRACT FROM AUTHOR]

This study outlines a detailed investigation using CCD UBV and Gaia DR3 data sets of the two open clusters Ruprecht 1 (Rup‐1) and Ruprecht 171 (Rup‐171). Fundamental astrophysical parameters such as color excesses, photometric metallicities, ages, and isochrone distances were based on UBV‐data analyses, whereas membership probability calculations, structural and astrophysical parameters, as well as the kinematic analyses were based on Gaia DR3‐data. We identified 74 and 596 stars as the most probable cluster members with membership probabilities over 50% for Rup‐1 and Rup‐171, respectively. The color excesses E(B−V)$$ E\left(B-V\right) $$ were obtained as 0.166±0.022$$ 0.166\pm 0.022 $$ and 0.301±0.027$$ 0.301\pm 0.027 $$ mag for Rup‐1 and Rup‐171, respectively. Photometric metallicity analyses were performed by considering F‐G type main‐sequence member stars and found to be [Fe/H]=−0.09±0.16$$ \left[\mathrm{Fe}/\mathrm{H}\right]=-0.09\pm 0.16 $$ and [Fe/H]=−0.20±0.20$$ \left[\mathrm{Fe}/\mathrm{H}\right]=-0.20\pm 0.20 $$ dex for Rup‐1 and Rup‐171, respectively. Ages and distances were based on both UBV and Gaia‐data analyses; according to isochrone‐fitting these values were estimated to be t=580±60$$ t=580\pm 60 $$ Myr, d=1469±57$$ d=1469\pm 57 $$ pc for Rup‐1 and t=2700±200$$ t=2700\pm 200 $$ Myr, d=1509±69$$ d=1509\pm 69 $$ pc for Rup‐171. The present‐day mass function slope of Rup‐1 was estimated as 1.26±0.32$$ 1.26\pm 0.32 $$ and Rup‐171 as 1.53±1.49$$ 1.53\pm 1.49 $$. Galactic orbit integration analyses showed that both of the clusters might be formed outside the solar circle. [ABSTRACT FROM AUTHOR]

The dark matter halos associated with galaxies have hitherto established strong correlations within a range of observed parameters, known as scaling relations of dark matter halos. The origin of these scaling relations still contains significant ambiguities and requires comprehensive exploration for complete understanding. Utilising the correlation between the concentration and mass of dark matter halos inferred from cosmological N -body simulations based on the cold dark matter paradigm (c – M relation), we derive theoretical scaling relations among other physical quantities, such as the surface mass density, the maximum circular velocity, and the scale radius of the dark matter halo. By comparing theoretical and observed scaling relations at various mass scales, it is found that the scaling relations observed in dwarf galaxies and galaxies originate in the c – M relation of the dark matter halo. We predict that this theoretical scaling relation is also established in galaxy clusters. Moreover, we propose a novel theoretical scaling relation that incorporates the effects of the cusp-to-core transition, which is supposed to occur in cold dark matter halos. Our discussion concludes with the exploration of potential observational verification of the cusp-to-core transition process in dark matter halos. [ABSTRACT FROM AUTHOR]

We employ the IllustrisTNG simulation data to investigate the turbulent and thermal motions of the cosmic baryonic fluid. With continuous wavelet transform techniques, we define the pressure spectra, or density-weighted velocity power spectra, as well as the spectral ratios, for both turbulent and thermal motions. We find that the magnitude of the turbulent pressure spectrum grows slightly from |$z=4$| to 2 and increases significantly from |$z=2$| to 1 at large scales, suggesting progressive turbulence injection into the cosmic fluid, whereas from |$z=1$| to 0, the spectrum remains nearly constant, indicating that turbulence may be balanced by energy transfer and dissipation. The magnitude of the turbulent pressure spectra also increases with environmental density, with the highest density regions showing a turbulent pressure up to six times that of thermal pressure. We also explore the dynamical effects of turbulence and thermal motions, discovering that while thermal pressure provides support against structure collapse, turbulent pressure almost counteracts this support, challenging the common belief that turbulent pressure supports gas against overcooling. [ABSTRACT FROM AUTHOR]

Differences between the local value of the Hubble constant measured via the distance ladder versus the value inferred from the cosmic microwave background with the assumption of the standard ΛCDM model have reached over 5 σ significance. To determine if this discrepancy is due to new physics or more mundane systematic errors, it is essential to remove as many sources of systematic uncertainty as possible, by developing high-precision distance ladders that are independent of the traditional Cepheid and Type Ia supernova route. Here, we present JWST observations of three early-type Fornax Cluster galaxies, the first of 14 observations from a Cycle 2 JWST program. Our modest integration times allow us to measure highly precise tip of the red giant branch (TRGB) distances and they will also be used to perform measurements of surface brightness fluctuations (SBFs). From these three galaxies, we determine an average TRGB distance modulus to the Fornax Cluster of μ = 31.424 ± 0.077 mag or D = 19.3 ± 0.7 Mpc. With 11 more scheduled observations in nearby elliptical galaxies, our program will allow us to set the zero-point of the SBF scale to better than 2% for more distant measurements, charting a path toward a high-precision measurement of H 0 that is independent of the traditional Cepheid–supernova Ia distance ladder. [ABSTRACT FROM AUTHOR]

Satellite galaxies can be used to indicate the dynamic mass of galaxy groups and clusters. In this study, we apply the axisymmetric Jeans Anisotropic Multi-Gaussian Expansion (JAM) modeling to satellite galaxies in 28 galaxy clusters selected from the TNG300-1 simulation with halo masses of log 10 M 200 / M ⊙ > 14.3 . If using true bound satellites as tracers, the best constrained total mass within the half-mass radius of satellites, M (< r half), and the virial mass, M 200, have average biases of −0.01 and 0.03 dex, with average scatters of 0.11 dex and 0.15 dex. If selecting companions in the redshift space with a line-of-sight depth of 2000 km s−1, the biases are −0.06 and 0.01 dex, while the scatters are 0.12 and 0.18 dex for M (< r half) and M 200. By comparing the best-fitting and actual density profiles, we find that ∼29% of the best-fitting density profiles show very good agreement with the truth, ∼32% display over/underestimates at most of the radial range with biased M (< r half), and 39% show under/overestimates in central regions and over/underestimates in the outskirts, with good constraints on M (< r half); yet most of the best constraints are still consistent with the true profiles within 1 σ statistical uncertainties for the three circumstances. Using a mock DESI Bright Galaxy Survey catalog with the effect of fiber incompleteness, we find DESI fiber assignments and the choice of flux limits barely modify the velocity dispersion profiles and are thus unlikely to affect the dynamical modeling outcomes. Our results show that with current and future deep spectroscopic surveys, JAM can be a powerful tool to constrain the underlying density profiles of individual massive galaxy clusters. [ABSTRACT FROM AUTHOR]

Abell 514 (A514) at z = 0.071 is an intriguing merging system exhibiting highly elongated (∼1 Mpc) X-ray features and three large-scale (300 ∼ 500 kpc) bent radio jets. To dissect this system with its multiwavelength data, it is critical to robustly identify and quantify its dark matter substructures. We present a weak-lensing analysis of A514 using deep Magellan/Megacam observations. Combining two optical band filter imaging data obtained under optimal seeing (∼0.″6) and leveraging the proximity of A514, we achieve a high source density of ∼ 46 arcmin − 2 or ∼6940 Mpc−2, which enables high-resolution mass reconstruction. We unveil the complex dark matter substructures of A514, which are characterized by the NW and SE subclusters separated by ∼0.7 Mpc, each exhibiting a bimodal mass distribution. The total mass of the NW subcluster is estimated to be M 200 c NW = 1.08 − 0.22 + 0.25 × 10 14 M ⊙ and is further resolved into the eastern ( M 200 c NW E = 2.6 − 1.1 + 1.4 × 10 13 M ⊙) and western ( M 200 c NW W = 7.1 − 2.0 + 2.3 × 10 13 M ⊙ ) components. The mass of the SE subcluster is M 200 c SE = 1.55 − 0.26 + 0.28 × 10 14 M ⊙ , which is also further resolved into the northern ( M 200 c SE N = 2.9 − 1.3 + 1.8 × 10 13 M ⊙ ) and southern ( M 200 c SE S = 8.5 − 2.6 + 3.1 × 10 13 M ⊙ ) components. These four substructures coincide with the A514 brightest galaxies and are detected with significances ranging from 3.3 σ to 4.7 σ. Comparison of the dark matter substructures with the X-ray distribution suggests that A514 might have experienced an off-axis collision, and the NW and SE subclusters are currently near their apocenters. [ABSTRACT FROM AUTHOR]

We present a combined strong and weak gravitational-lensing analysis of the massive galaxy cluster MACS J1423.8+2404 (⁠|$z=0.545$|⁠ , MACS J1423 hereafter), one of the most dynamically relaxed and massive cool-core clusters discovered in the MAssive Cluster Survey at |$z\gt 0.5$|⁠. We combine high-resolution imaging from the Hubble Space Telescope (HST) in the F 606 W, F 814 W , and F 160 W pass-bands with spectroscopic observations taken as part of the KALEIDOSCOPE survey with the Multi-Unit Spectroscopic Explorer mounted on the Very Large Telescope. Our strong lensing analysis of the mass distribution in the cluster core is constrained by four multiple-image systems (17 individual images) within redshift range |$1.779\lt z\lt 2.840$|⁠. Our weak lensing analysis of the cluster outskirts, confined to the HST field of view, is based on a background galaxy catalogue with a density of 57 gal arcmin |$^{-2}$|⁠. We measure a projected mass of |$M(R\lt 200$|  kpc) = (1.6 |$\pm$| 0.05) |$\times$| 10 |$^{14}$|  M |$_{\rm \odot }$| from our strong lensing model, and a projected mass of |$M(R\lt 640$|  kpc) = (6.6 |$\pm$| 0.6) |$\times$| 10 |$^{14}$|  M |$_{\rm \odot }$| when combining with our the weak lensing constraints. Our analysis of the cluster mass distribution yields no evidence of substructures, confirming the dynamically relaxed state of MACS J1423. Our work sets the stage for future analysis of MACS J1423 in the upcoming Canadian Near-Infrared Imager and Stiltless Spectrograph Unbiased Cluster Survey for the JWST. [ABSTRACT FROM AUTHOR]

Early-type dwarf galaxies constitute a prevalent population in the central regions of rich groups and clusters in the local Universe. These low-luminosity and low-mass stellar systems play a fundamental role in the assembly of the luminous galaxies observed today, according to the Lambda cold dark matter hierarchical theory. The origin of early-type dwarfs has been linked to the transformation of disc galaxies interacting with the intracluster medium, especially in dense environments. However, the existence of low-luminosity early-type galaxies in low-density environments presents a challenge to this scenario. This study presents a comprehensive photometric and spectroscopic analysis of the early-type dwarf galaxy CGCG014−074 using deep Gemini GMOS (Gemini Multi-Object Spectrograph) data, focusing on its peculiarities and evolutionary implications. CGCG014−074 exhibits distinct features, including a rotating inner disc, an extended stellar formation with a quiescent phase since about 2 Gyr ago, and the presence of boxy isophotes. From the kinematic analysis, we confirm CGCG014−074 as a nucleated early-type dwarf galaxy with embedded disc. The study of its stellar population parameters using different methods provides significant insights into the galaxy's evolutionary history. These results show an old and metal-poor nucleus (⁠|${\sim}9.3$| Gyr and |$\mathrm{[Z/H]}\sim -0.84$| dex), while the stellar disc is younger (⁠|${\sim}4.4$| Gyr) with a higher metallicity (⁠|$\mathrm{[Z/H]}\sim -0.40$| dex). These distinctive features collectively position CGCG014−074 as a likely building block galaxy that has evolved passively throughout its history. [ABSTRACT FROM AUTHOR]

Milky Way analogues (MWAs) provide an alternative insight into the various pathways that lead to the formation of disc galaxies with similar properties to the Milky Way (MW). In this study, we explore different selection techniques for identifying MWAs in the Sydney-AAO (Australian Astronomical Observatory) Multi-object Integral field spectrograph (SAMI) Galaxy Survey. We utilize a nearest neighbours method to define MWAs using four selection parameters including stellar mass (⁠|$M_{\star }$|⁠), star formation rate (⁠|$\rm SFR$|⁠), bulge-to-total ratio (⁠|$B/T$|⁠), and disc effective radius (⁠|$R_{\rm {e}}$|⁠). Based on 15 different selection combinations, we find that including |$M_{\star }$| and SFR is essential for minimizing biases in the average MWA properties as compared to the MW. Furthermore, given the MW's smaller than average size, selection combinations without |$R_{\rm {e}}$| result in MWAs being too large. Lastly, we find that |$B/T$| is the least important parameter out of the four tested parameters. Using all four selection criteria, we define the top 10 most MW-like galaxies in the GAMA and Cluster regions of the SAMI survey. These most MW-like galaxies are typically barred spirals, with kinematically cold rotating discs and reside in a wide range of environments. Surprisingly, we find no significant differences between the MWAs selected from the GAMA and Cluster regions. Our work highlights the importance of using multiple selection criteria for finding MWAs and also demonstrates potential biases in previous MWA studies. [ABSTRACT FROM AUTHOR]

One necessary step for probing the nature of self-interacting dark matter (SIDM) particles with astrophysical observations is to pin down any possible velocity dependence in the SIDM cross-section. Major challenges for achieving this goal include eliminating, or mitigating, the impact of the baryonic components and tidal effects within the dark matter halos of interest – the effects of these processes can be highly degenerate with those of dark matter self-interactions at small scales. In this work, we select 9 isolated galaxies and brightest cluster galaxies (BCGs) with baryonic components small enough such that the baryonic gravitational potentials do not significantly influence the halo gravothermal evolution processes. We then constrain the parameters of Rutherford and Møller scattering cross-section models with the measured rotation curves and stellar kinematics through the gravothermal fluid formalism and isothermal method. Cross-sections constrained by the two methods are consistent at |$1\sigma$| confidence level, but the isothermal method prefers cross-sections greater than the gravothermal approach constraints by a factor of |$\sim 3$|⁠. [ABSTRACT FROM AUTHOR]

The characteristics of the young stellar population in the nearby irregular galaxy NGC 2366 were investigated. In particular, we focused our attention on its hierarchical clustering distributions and the properties of the stellar groups. This galaxy exhibits a prominent blue helium-burning star feature in the colour-magnitude diagram, suggesting that it has undergone an extended period of stellar formation. The galaxy was observed in two bands by the Hubble Space Telescope covering almost its complete central and intermediate parts, including all the major stellar formation regions. Available photometric data allowed us to select the blue and young stars and, therefore, study the recent stellar formation. Through the path linkage criterion (PLC), we found 23 young star groups and estimated their fundamental parameters, such as their stellar densities, sizes, and number of members. We also performed a fractal substructure analysis to determine the clustering properties of this population, and we built a stellar density map corresponding to the galactic young population. We found that most of the young stellar groups have stars that have a distribution of locations that is compatible with a fractal dimension. [ABSTRACT FROM AUTHOR]

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 μ G within the IGrM and 0.1–1 μ G 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. [ABSTRACT FROM AUTHOR]

Gaia Data Release 3 (DR3) provides the first classifications for the sources in Gaia 's all-sky database. Most Gaia sources are stars in the Milky Way, but DR3 also contains many sources that belong to nearby galaxies, as well as background galaxies and quasars. In this work, we compare the Gaia classifications from the Discrete Source Classifier (CU8-DSC) module to the more detailed and heterogeneous classifications in NED (NASA Extragalactic Database) and/or SIMBAD (Set of Identifications, Measurements and Bibliography for Astronomical Data) for sources with sky positions within twice the Holmberg radius of nearby galaxies. Matching these catalogues gives approximately |$3.2\times 10^5$| unique Gaia matches for |$4\times 10^5$| sources over 1040 galaxies (excluding some large Local Group galaxies) in the Local Volume Galaxy catalogue. Matched sources contain a lower fraction of Gaia -classified stars and higher fractions of galaxies and quasars (⁠|$\sim 95$| per cent, 2 per cent, and 2 per cent, respectively) than DR3 overall. Considering NED (SIMBAD) classifications as truth values, the balanced accuracy of Gaia classification is 0.80 (0.83): the most common disagreements are literature-classified galaxies Gaia -classified as stars and literature-classified stars Gaia -classified as quasars. Purity (P) and completeness (C) metrics show that agreement between Gaia classification and NED/SIMBAD classification is best for stars (⁠|$P\, \mathrm{ and}\, C\sim 0.9$|⁠), and decreases for quasars (⁠|$P\lt 0.3$| and |$0.7\lt C\lt 0.8$|⁠), galaxies (⁠|$0.7\lt P\lt 0.8$| and |$0.3\lt C\lt 0.6$|⁠), white dwarfs (⁠|$0.04\lt P\lt 0.6$| and |$C\sim 0.6$|⁠), and binary stars (⁠|$P\, \mathrm{ and}\, C\lt 0.1$|⁠). NED or SIMBAD sources classified only by detection wavelength are most often Gaia -classified as stars, while non-stellar components of galaxies appear in all Gaia classes. [ABSTRACT FROM AUTHOR]

The forthcoming generation of radio telescope arrays promises significant advancements in sensitivity and resolution, enabling the identification and characterization of many new faint and diffuse radio sources. Conventional manual cataloguing methodologies are anticipated to be insufficient to exploit the capabilities of new radio surveys. Radio interferometric images of diffuse sources present a challenge for image segmentation tasks due to noise, artifacts, and embedded radio sources. In response to these challenges, we introduce Radio U-Net, a fully convolutional neural network based on the U-Net architecture. Radio U-Net is designed to detect faint and extended sources in radio surveys, such as radio haloes, relics, and cosmic web filaments. Radio U-Net was trained on synthetic radio observations built upon cosmological simulations and then tested on a sample of galaxy clusters, where the detection of cluster diffuse radio sources relied on customized data reduction and visual inspection of Low-Frequency Array Two metre Sky Survey (LoTSS) data. The 83 per cent of clusters exhibiting diffuse radio emission were accurately identified, and the segmentation successfully recovered the morphology of the sources even in low-quality images. In a test sample comprising 246 galaxy clusters, we achieved a 73 per cent accuracy rate in distinguishing between clusters with and without diffuse radio emission. Our results establish the applicability of Radio U-Net to extensive radio survey data sets, probing its efficiency on cutting-edge high-performance computing systems. This approach represents an advancement in optimizing the exploitation of forthcoming large radio surveys for scientific exploration. [ABSTRACT FROM AUTHOR]

Galaxy clusters are important probes for both cosmology and galaxy formation physics. We test the cosmological, hydrodynamical FLAMINGO (Full-hydro large-scale structure simulations with all-sky mapping for the interpretation of next generation observations) simulations by comparing to observations of the gaseous properties of clusters measured from X-ray observations. FLAMINGO contains unprecedented numbers of massive galaxy groups (⁠|$\gt 10^6$|⁠) and clusters (⁠|$\gt 10^5$|⁠) and includes variations in both cosmology and galaxy formation physics. We predict the evolution of cluster scaling relations as well as radial profiles of the temperature, density, pressure, entropy, and metallicity for different masses and redshifts. We show that the differences between volume-, and X-ray-weighting of particles in the simulations, and between cool- and non-cool-core samples, are similar in size as the differences between simulations for which the stellar and AGN (active galactic nucleus) feedback has been calibrated to produce significantly different gas fractions. Compared to thermally driven AGN feedback, kinetic jet feedback calibrated to produce the same gas fraction at |$R_{\rm 500c}$| yields a hotter core with higher entropies and lower densities, which translates into a smaller fraction of cool-core clusters. Stronger feedback, calibrated to produce lower gas fractions and hence lower gas densities, results in higher temperatures, entropies, and metallicities, but lower pressures. The scaling relations and thermodynamic profiles show almost no evolution with respect to self-similar expectations, except for the metallicity decreasing with redshift. We find that the temperature, density, pressure, and entropy profiles of clusters in the fiducial FLAMINGO simulation are in excellent agreement with observations, while the metallicities in the core are too high. [ABSTRACT FROM AUTHOR]

New, deep HST photometry allowed us to identify and study eight compact and bright (MV ≤ −5.8) star clusters in the outskirts of the star-forming isolated dwarf galaxy NGC 5238 (M* ≃ 108 M⊙). Five of these clusters are new discoveries, and six appear projected onto and/or aligned with the tidal tails recently discovered around this galaxy. The clusters are partially resolved into stars, and their colour magnitude diagrams reveal a well-developed red giant branch, implying ages older than 1–2 Gyr. Their integrated luminosity and structural parameters are typical of classical globular clusters, and one of them, with MV = −10.56 ± 0.07, is as bright as ω Cen, the brightest globular cluster in the Milky Way. Since the properties of this cluster are in the range spanned by those of nuclear star clusters we suggest that it may be the nuclear remnant of the disrupted satellite of NGC 5238 that produced the observed tidal tails. [ABSTRACT FROM AUTHOR]

Context. X-shaped radio galaxies (XRGs) are characterised by two pairs of misaligned lobes: active lobes hosting radio jets and the wings. None of the formation mechanisms proposed thus far are able to exhaustively reproduce the diverse features observed among XRGs. Emerging evidence has proposed the existence of sub-populations of XRGs forming via different processes. Aims. The brightest cluster galaxy (BCG) in Abell 3670 (A3670) is a dumbbell system hosting the XRG MRC 2011-298. The morphological and spectral properties of this interesting XRG were first characterised based on Karl G. Jansky Very Large Array (JVLA) data at 1–10 GHz. In the present work, we follow up on MRC 2011-298 with the upgraded Giant Metrewave Radio Telescope (uGMRT) at 120–800 MHz to further constrain its properties and origin. Methods. We carried out a detailed spectral analysis sampling different spatial scales. Integrated radio spectra, spectral index maps, radio colour-colour diagrams, and radiative age maps of both the active lobes and prominent wings were employed to test the origin of the source. Results. We confirm a progressive spectral steepening from the lobes to the wings. The maximum radiative age of the source is ~80 Myr, with the wings being older than the lobes by ≳30 Myr in their outermost regions. Conclusions. The observed properties are in line with an abrupt reorientation of the jets by ~90 deg from the direction of the wings to their present position. This formation mechanism is further supported by the comparison with numerical simulations in the literature, which additionally highlight the role of hydrodynamic processes in the evolution of large wings such as those of MRC 2011-298. It is plausible that the coalescence of supermassive black holes could have triggered the spin-flip of the jets. Moreover, we show that the S-shape of the radio jets is likely driven by precession with a period of P ~ 10 Myr. [ABSTRACT FROM AUTHOR]

Context. Abell 754 is a rich galaxy cluster at z = 0.0543 and is considered the prototype of a major cluster merger. As many dynamically unrelaxed systems, it hosts diffuse radio emission on megaparsec-scales. Extended synchrotron sources in the intra-cluster medium (ICM) are commonly interpreted as evidence that a fraction of the gravitational energy released during cluster mergers is dissipated into nonthermal components. Aims. Here, we aim to use new MeerKAT UHF- and L-band observations to study nonthermal phenomena in Abell 754. These data are complemented with archival XMM-Newton observations to investigate the resolved spectral properties of both the radio and X-ray cluster emission. Methods. For the first time, we employed the pipeline originally developed to calibrate LOFAR data to MeerKAT observations. This allowed us to perform a direction-dependent calibration and obtain highly sensitive radio images in UHF and L bands that capture the extended emission with unprecedented detail. By using a large XMM-Newton mosaic, we produced thermodynamic maps of the ICM. Results. Our analysis reveals that the radio halo in the cluster center is bounded by the well-known shock in the eastern direction. Furthermore, in the southwest periphery, we discover an extended radio source that we classify as a radio relic that is possibly tracing a shock driven by the squeezed gas compressed by the merger, outflowing in perpendicular directions. The low-luminosity of this relic appears compatible with direct acceleration of thermal pool electrons. We interpret the observed radio and X-ray features in the context of a major cluster merger with a nonzero impact parameter. Conclusions. Abell 754 is a remarkable galaxy cluster showcasing exceptional features associated with the ongoing merger event. The high quality of the new MeerKAT data motivates further work on this system. [ABSTRACT FROM AUTHOR]

The observation of a massive galaxy with an extremely low dark matter content (i.e. NGC 1277) has posed questions about how such objects form and evolve in a hierarchical universe. We here report on the finding of several massive, dark matter-deficient galaxies in a set of 324 galaxy clusters theoretically modelled by means of full-physics hydrodynamical simulations. We first focus on two example galaxies selected amongst the most massive and dark matter-deficient ones. By tracing the evolution of these galaxies, we find that their lack of dark matter is a result of multiple pericentre passages. While orbiting their host halo, tidal interactions gradually strip away dark matter while preserving the stellar component. A statistical analysis of all massive satellite galaxies in the simulated clusters shows that the stellar-to-total mass ratio today is strongly influenced by the number of orbits and the distance at pericentres. Galaxies with more orbits and closer pericentres are more dark matter-deficient. Additionally, we find that massive, dark matter-deficient galaxies at the present day are either the remnants of very massive galaxies at infall or former central galaxies of infalling groups. We conclude that such massive yet dark matter-deficient galaxies exist and are natural by-products of typical cluster galaxy evolution, with no specific requirement for an exotic formation scenario. [ABSTRACT FROM AUTHOR]

Galaxy clusters are useful cosmological probes and interesting astrophysical laboratories. As the cluster samples continue to grow in size, a deeper understanding of the sample characteristics and improved control of systematics becomes more crucial. For this analysis we created a new and larger ACT-DR5-based thermal Sunyaev–Zel'dovich Effect- (tSZE-) selected galaxy cluster catalog with improved control over sample purity and completeness. We employed the red sequence based cluster redshift and confirmation tool MCMF together with optical imaging data from the Legacy Survey DR-10 and infrared data from the WISE satellite to systematically identify true clusters from a new cluster candidate detection run on the ACT-DR5 dataset. The resulting ACT-DR5 MCMF sample contains 6,237 clusters with a residual contamination of 10.7%. This is an increase of 49% compared to the previous ACT-DR5 cluster catalog, making this new catalog the largest tSZE-selected cluster catalog to date. The zphot>1 subsample contains 703 clusters, three times more than in the previous ACT-DR5 catalog. Cross-matching the ACT-DR5 MCMF cluster catalog with a deeper tSZE sample from SPTpol 500d allows us to confirm the completeness and purity of the new ACT-DR5 MCMF sample. Cross-matching to the two largest X-ray-selected cluster samples, the all-sky RASS MCMF and the western Galactic hemisphere survey eRASS1, confirms the sample purity of the RASS MCMF sample and in the case of eROSITA eRASS1 reveals that 43% of the matched clusters are designated in eRASS1 as X-ray point sources rather than groups and clusters. Cross-correlating the ACT-DR5 MCMF cluster catalog with ACT-DR6 lensing maps results in a 16.4σ detection of Cosmic Microwave Background (CMB) lensing around the clusters, corresponding to the strongest signal found so far for a galaxy cluster sample. Repeating the measurement for the z > 1 cluster subsample yields a significance of 4.3σ, which is the strongest CMB lensing detection in a z>1 cluster sample to date. [ABSTRACT FROM AUTHOR]

Galaxy evolution depends on the environment in which galaxies are located. The various physical processes (ram-pressure stripping, tidal interactions, etc.) that are able to affect the gas content in galaxies have different efficiencies in different environments. In this work, we examine the gas (atomic HI and molecular H2) content of local galaxies inside and outside clusters, groups, and filaments as well as in isolation using a combination of observational and simulated data. We exploited a catalogue of galaxies in the Virgo cluster (including the surrounding filaments and groups) and compared the data against the predictions of the Galaxy Evolution and Assembly (GAEA) semi-analytic model, which has explicit prescriptions for partitioning the cold gas content in its atomic and molecular phases. We extracted from the model both a mock catalogue that mimics the observational biases and one not tailored to observations in order to study the impact of observational limits on the results and predict trends in regimes not covered by the current observations. The observations and simulated data show that galaxies within filaments exhibit intermediate cold gas content between galaxies in clusters and in isolation. The amount of HI is typically more sensitive to the environment than H2 and low-mass galaxies (log10[M⋆/M⊙]< 10) are typically more affected than their massive (log10[M⋆/M⊙]> 10) counterparts. Considering only model data, we identified two distinct populations among filament galaxies present in similar proportions: those simultaneously lying in groups and isolated galaxies. The former has properties more similar to cluster and group galaxies, and the latter is more similar to those of field galaxies. We therefore did not detect the strong effects of filaments themselves on the gas content of galaxies, and we ascribe the results to the presence of groups in filaments. [ABSTRACT FROM AUTHOR]