Merging Systems Research Articles

Strategic Innovation: Integrating System Dynamics into Management Control

This article explores the concept of strategic innovation, with a focus on its integration with system dynamics in the field of management control. By examining the synergies between these two domains, the article proposes innovative perspectives to enhance decision-making processes and overall business management. The authors highlight the benefits of adopting a systemic approach in management control, emphasizing how it can foster a deeper understanding of complex interactions within organizations. Practical case studies illustrate how this integration can lead to significant innovations, providing managers with valuable tools to navigate in an ever-evolving business environment. Ultimately, the article underscores the strategic importance of merging systems thinking with management control to promote more effective, resilient, and future-oriented business management.

Does the HCN/CO ratio trace the fraction of gravitationally bound gas? II. Variations in CO and HCN emissivity

We modeled emissivities of the HCN and CO $J=1-0$ transitions across a grid of molecular cloud models encapsulating observed properties that span from normal star-forming galaxies to more extreme merging systems. These models are compared with archival observations of the HCN and CO $J=1-0$ transitions, in addition to the radio continuum at 93 GHz, for ten nearby galaxies. We combined these model emissivities with the predictions of gravoturbulent models of star formation presented in the first paper in this series. In particular, we explored the impact of excitation and optical depth on CO and HCN emission and assess if the HCN/CO ratio tracks the fraction of gravitationally bound dense gas, $f_ grav $, in molecular clouds. We find that our modeled HCN/CO ratios are consistent with the measurements within our sample, and our modeled HCN and CO emissivities are consistent with the results of observational studies of nearby galaxies and clouds in the Milky Way. CO emission shows a wide range of optical depths across different environments, ranging from optically thick in normal galaxies to moderately optically thin in more extreme systems. HCN appears only moderately optically thick and shows significant subthermal excitation in both normal and extreme galaxies. We find an anticorrelation between HCN/CO and $f_ grav $, which implies that the HCN/CO ratio is not a reliable tracer of $f_ grav $. Instead, this ratio appears to best track gas at moderate densities ($n>10^ cm $), which is below the typically assumed dense gas threshold of $n>10^ cm $. We also find that variations in CO emissivity depend strongly on optical depth, which is a product of variations in the dynamics of the cloud gas. HCN emissivity is more strongly dependent on excitation, as opposed to optical depth, and thus does not necessarily track variations in CO emissivity. We further conclude that a single line ratio, such as HCN/CO, will not consistently track the fraction of gravitationally bound, star-forming gas if the critical density for star formation varies in molecular clouds. This work highlights important uncertainties that need to be considered when observationally applying an HCN conversion factor in order to estimate the dense (i.e.,\ cm $) gas content in nearby galaxies.

An optically dark merging system at z ∼ 6 detected by JWST

Context. Near- to mid-infrared observations (from Spitzer and JWST) have revealed a hidden population of galaxies at redshift z = 3 − 6 called optically dark objects, which are believed to be massive and dusty star-formers. They contribute substantially to the cosmic star-formation rate (SFR) density at z ∼ 4 − 5 (up to 30 − 40%). Aims. While optically dark sources are widely recognized as a significant component of the stellar mass function, the history of their stellar mass assembly (and the evolution of their interstellar medium) remains unexplored. However, they are thought to be the progenitors of the more massive early-type galaxies found in present-day groups and clusters. It is thus important to examine the possible connection between dark sources and merging events in order to understand the environment in which they live. Methods. Here, we report our search for close companions in a sample of 19 optically-dark objects identified in the SMACS0723 JWST deep field. They were selected in the NIRCam F444W band and undetected below 2 μm. We restricted our analysis to the reddest (i.e., F277W–F444W > 1.3) and brightest (F444W < 26 mag) objects. Results. We identified KLAMA, an optically dark source showing a very close companion (angular distance < 0.5″). The spatially resolved SED fitting procedure indicates that all components lying within 1.5″ of who is it the dark source are indeed at z ∼ 5.7. Tidal features (leading to a whale-shaped morphology) corroborate the hypothesis that KLAMA is the most massive (log(M⋆/M⊙) > 10.3) and dusty (AV ∼ 3 at the core) system of an ongoing merger with a mass ratio of ∼10. Thus, around ten similar merger events would be required to double the stellar mass of KLAMA. Merging systems with properties similar to KLAMA are identified in the SERRA simulations, allowing us to reconstruct their stellar-mass assembly history and predict their molecular gas properties (in particular, the [CII] emission for the simulated system). Conclusions. The discovery of mergers within dark galaxies at the end of the Epoch of Reionization highlights the importance of conducting a statistical search for additional candidates in deep NIRCam fields. Such research will aid in our understanding of the significance of merging processes during the obscured phase of stellar-mass accumulation.

Hidden by a star: The redshift and the offset broad line of the flat-spectrum radio quasar PKS 0903–57

Context. PKS 0903−57 is a little-studied γ-ray blazar that has recently attracted considerable interest due to the strong flaring episodes observed since 2020 in high energy (HE; 100 MeV ≤ E ≤ 100 GeV) and very high-energy (VHE; 100 GeV ≤ E ≤ 10 TeV) γ-rays. Its nature and properties are still not well determined. In particular, it is unclear whether PKS 0903−57 is a BL Lac or a flat-spectrum radio quasar (FSRQ), while its redshift estimation relies on a possibly misassociated low signal-to-noise ratio spectrum. Aims. Our aims were to reliably measure the redshift of the blazar, and to determine its spectral type and luminosity in the optical range. Methods. We performed spectroscopy of the optical counterpart of the blazar using the South African Large Telescope (SALT) and the Very Large Telescope (VLT), and monitored it photometrically with the Rapid Eye Mount (REM) telescope. Results. We firmly measured the redshift of the blazar as z = 0.2621 ± 0.0006 thanks to the detection of five narrow optical lines. The detection of a symmetric broad Hα line with full width at half maximum (FWHM) of 4020 ± 30 km/s together with a jet-dominated continuum leads us to classify it as a FSRQ. Finally, we detected with high significance a redshift offset (∼1500 km/s) between the broad line and the host. This is the first time that such an offset has been unequivocally detected in a VHE blazar, possibly pointing to a very peculiar accretion configuration, a merging system, or a recoiling black hole.

JWST View of Four Infant Galaxies at z = 8.31–8.49 in the MACS J0416.1−2403 Field and Implications for Reionization

New JWST/NIRCam wide-field slitless spectroscopy provides redshifts for four z > 8 galaxies located behind the lensing cluster MACS J0416.1−2403. Two of them, “Y1” and “JD,” have previously reported spectroscopic redshifts based on Atacama Large Millimeter/submillimeter Array measurements of [O iii] 88 μm and/or [C ii] 157.7 μm lines. Y1 is a merging system of three components, and the existing redshift z = 8.31 is confirmed. However, JD is at z = 8.34 instead of the previously claimed z = 9.28. JD’s close companion, “JD-N,” which was a previously discovered z > 8 candidate, is now identified at the same redshift as JD. JD and JD-N form an interacting pair. A new candidate at z > 8, “f090d_018,” is also confirmed and is at z = 8.49. These four objects are likely part of an overdensity that signposts a large structure extending ∼165 kpc in projected distance and ∼48.7 Mpc in radial distance. They are magnified by less than 1 mag and have an intrinsic M UV ranging from −19.57 to −20.83 mag. Their spectral energy distributions show that the galaxies are all very young with ages ∼ 4–18 Myr and stellar masses of about 107–8 M ⊙. These infant galaxies have very different star formation rates ranging from a few to over a hundred solar masses per year, but only two of them (JD and f090d_018) have blue rest-frame UV slopes β < −2.0 indicative of a high Lyman-continuum photon escape fraction that could contribute significantly to the cosmic hydrogen-reionizing background. Interestingly, these two galaxies are the least massive and least active ones among the four. The other two systems have much flatter UV slopes largely because of their high dust extinction (A V = 0.9–1.0 mag). Their much lower indicated escape fractions show that even very young, actively star-forming galaxies can have a negligible contribution to reionization when they quickly form dust throughout their bodies.

Development and safety evaluation of an adaptive personalized speed guidance system for on-ramp merging in highway service areas

As autonomous driving and Vehicle-to-Everything (V2X) technologies evolve, the efficiency and safety of ramp merging in the highway service areas have become increasing critical. This study introduces a closed-loop feedback speed guidance system that accommodates individual driving styles, aiming to optimize merging behaviour, reduce traffic accidents, and enhance total traffic efficiency. The system dynamically adjusts the merging vehicle speeds by continuously monitoring their speed and location with variable steps to promote smoother merging. Moreover, this research also involves collecting naturalistic driving data from ramp merging scenarios, using the K-means clustering and point estimation method to recognize and analyse driving style characteristics, and integrating these styles into the developed closed-loop feedback speed guidance system. This approach results in personalized speed guidance curves tailored to different driving styles, facilitating more efficient mering. Additionally, the study conducts a Safety of the Intended Functionality (SOTIF) evaluation of this system using the System-Theoretic Process Analysis (STPA) method, which helps identify potential security risks and develop appropriate mitigation strategies to ensure the system’s safe and stable operation. The simulation results confirm that this innovative dynamic speed guidance system substantially improves traffic safety and efficiency in ramp merging areas.

Merging Signatures in an Offset Lyman Continuum Emitter at Redshift 3.8

Lyman continuum (LyC) emitters at z > 3 provide critical samples for studying the contribution of galaxies to the ionizing background in the epoch of reionization. We collect a sample of z > 3 LyC emitters, a dominant fraction (∼60%–70%) of which show spatial offsets between LyC emission and the nonionizing continuum. From this sample, especially, we find a case of an offset LyC emitter, CDFS-6664 (z = 3.797), which shows two components in the high-resolution Hubble Space Telescope and James Webb Space Telescope images. The exceptionally rich data set of CDFS-6664 enables us to extract the two components across multiple wavelengths and estimate their physical properties. We show that CDFS-6664 is consistent with a major merger system with boosted star formation in both components and that the offset LyC emission is most likely associated with the bluer and younger component in this merging system. Our result offers an example in which the offset can be caused by a merger. Future observations of more offset LyC emitters would elucidate the role that mergers play in the escape of LyC photons.

Carbon envelopes around merging galaxies at z ∼ 4.5

Context. Galaxies evolve through a dynamic exchange of material with their immediate surrounding environment, the so-called circumgalactic medium (CGM). Understanding the physics of gas flows and the nature of the CGM is fundamental to studying galaxy evolution, especially at 4 ≤ z ≤ 6 (i.e., after the Epoch of Reionization) when galaxies rapidly assembled their masses and reached their chemical maturity. Galactic outflows are predicted to enrich the CGM with metals, although it has also been suggested that gas stripping in systems undergoing a major merger may play a role. Aims. In this work, we explore the metal enrichment of the medium around merging galaxies at z ∼ 4.5, observed by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE). To do so, we study the nature of the [CII] 158 μm emission in the CGM around these systems, using simulations to help disentangle the mechanisms contributing to the CGM metal pollution. Methods. By adopting an updated classification of major merger systems in the ALPINE survey, we selected and analyzed merging galaxies whose components can be spatially and/or spectrally resolved in a robust way. This makes it possible to distinguish between the [CII] emission coming from the single components of the system and that coming from the system as a whole. We also made use of the dustyGadget cosmological simulation to select synthetic analogs of observed galaxies and guide the interpretation of the observational results. Results. We find a large diffuse [CII] envelope (≳20 kpc) embedding all the merging systems, with at least 25% of the total [CII] emission coming from the medium between the galaxies. Using predictions from dustyGadget, we suggest that this emission has a multi-fold nature, with dynamical interactions between galaxies playing a major role in stripping the gas and enriching the medium with heavy elements.

LoVoCCS. II. Weak Lensing Mass Distributions, Red-sequence Galaxy Distributions, and Their Alignment with the Brightest Cluster Galaxy in 58 Nearby X-Ray-luminous Galaxy Clusters

The Local Volume Complete Cluster Survey is an ongoing program to observe nearly a hundred low-redshift X-ray-luminous galaxy clusters (redshifts 0.03 < z < 0.12 and X-ray luminosities in the 0.1–2.4 keV band L X500c > 1044 erg s−1) with the Dark Energy Camera, capturing data in the u, g, r, i, z bands with a 5σ point source depth of approximately 25th–26th AB magnitudes. Here, we map the aperture masses in 58 galaxy cluster fields using weak gravitational lensing. These clusters span a variety of dynamical states, from nearly relaxed to merging systems, and approximately half of them have not been subject to detailed weak lensing analysis before. In each cluster field, we analyze the alignment between the 2D mass distribution described by the aperture mass map, the 2D red-sequence (RS) galaxy distribution, and the brightest cluster galaxy (BCG). We find that the orientations of the BCG and the RS distribution are strongly aligned throughout the interiors of the clusters: the median misalignment angle is 19° within 2 Mpc. We also observe the alignment between the orientations of the RS distribution and the overall cluster mass distribution (by a median difference of 32° within 1 Mpc), although this is constrained by galaxy shape noise and the limitations of our cluster sample size. These types of alignment suggest long-term dynamical evolution within the clusters over cosmic timescales.

Substructures within Substructures in the Complex Postmerging System A514 Unveiled by High-resolution Magellan/Megacam Weak Lensing

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 ∼46arcmin−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 M200cNW=1.08−0.22+0.25×1014M⊙ and is further resolved into the eastern ( M200cNWE=2.6−1.1+1.4×1013M⊙) and western ( M200cNWW=7.1−2.0+2.3×1013M⊙ ) components. The mass of the SE subcluster is M200cSE=1.55−0.26+0.28×1014M⊙ , which is also further resolved into the northern ( M200cSEN=2.9−1.3+1.8×1013M⊙ ) and southern ( M200cSES=8.5−2.6+3.1×1013M⊙ ) components. These four substructures coincide with the A514 brightest galaxies and are detected with significances ranging from 3.3σ to 4.7σ. 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.

The rate and contribution of mergers to mass assembly from NIRCam observations of galaxy candidates up to 13.3 billion years ago

ABSTRACT We present an analysis of the galaxy merger rate in the redshift range $4.0\lt z\lt 9.0$ (i.e. about 1.5 to 0.5 Gyr after the big bang) based on visually identified galaxy mergers from morphological parameter analysis. Our data set is based on high-resolution NIRCam JWST data (a combination of F150W and F2000W broad-band filters) in the low-to-moderate magnification ($\mu \lt 2$) regions of the Abell 2744 cluster field. From a parent set of 675 galaxies $(M_{U}\in [-26.6,-17.9])$, we identify 64 merger candidates from the Gini, $M_{20}$ and asymmetry morphological parameters, leading to a merger fraction $f_m=0.11\pm 0.04$. There is no evidence of redshift evolution of $f_m$ even at the highest redshift considered, thus extending well into the epoch of reionization the constant trend seen previously at $z\lesssim 6$. Furthermore, we investigate any potential redshift-dependent differences in the specific star formation rates between mergers and non-mergers. Our analysis reveals no significant correlation in this regard, with deviations in the studied redshift range typically falling within $(1-1.5)\sigma$ from the null hypothesis that can be attributed to sample variance and measurement errors. Finally, we also demonstrate that the classification of a merging system is robust with respect to the observed (and equivalently rest frame) wavelength of the high-quality JWST broad-band images used. This preliminary study highlights the potential for progress in quantifying galaxy assembly through mergers during the epoch of reionization, with significant sample size growth expected from upcoming large JWST infrared imaging data sets.

Ideal Integration Approaches for Enhancing ASDP Group's Performance Post-Subsidiary Acquisition

Transportation plays a crucial role in the development of civilizations by enabling the movement of people, goods, and cultural exchanges. Among various transportation modes, water-based transport, especially ferries, is vital for linking communities, boosting trade, and promoting tourism in regions that land or air transport cannot reach. PT ASDP Indonesia Ferry (Persero), the sole state-owned enterprise managing ferry services in Indonesia, holds a leading position in the national ferry industry. To sustain its dominance, ASDP undertook a corporate action by acquiring a competitor. The acquisition process, dating back to the 1970s, involves stages of strategy formulation, investigation and selection, negotiation, and integration. According to Mroczynski, integration involves merging operations, cultures, and systems to achieve synergies and strategic goals. This study examines the optimal integration approach used by ASDP to enhance group performance post-acquisition. Utilizing a qualitative research method, focus group discussions were conducted with stakeholders from both ASDP and the acquired company. The study applies Pitkethly’s integration framework, which categorizes integration levels from minimal to extensive. Results show that ASDP has established significant financial management control over the acquired company, but gaps still exist between the desired and current conditions. Therefore, a detailed analysis of the targets ASDP needs to achieve to optimize the integration process is crucial for meeting post-acquisition requirements.

Very Long Baseline Interferometry Detection of an Active Radio Source Potentially Driving 100 kpc Scale Emission in the Ultraluminous Infrared Galaxy IRAS F01004–2237

The nearby ultraluminous infrared galaxy (ULIRG) IRAS F01004−2237 exhibits 100 kpc scale continuum emission at radio wavelengths. The absence of extended X-ray emission in IRAS F01004−2237 has suggested an active galactic nucleus (AGN) origin for the extended radio emission, whose properties and role in merging systems still need to be better understood. We present the results of multifrequency observations of IRAS F01004−2237 conducted by the Very Long Baseline Array at 2.3 and 8.4 GHz. Compact 8.4 GHz continuum emission was detected on a 1 pc scale in the nuclear region with an intrinsic brightness temperature of 108.1 K suggesting that the radio source originated from an AGN, potentially driving the extended emission. In contrast, no significant emission was observed at 2.3 GHz, indicating the presence of low-frequency absorption. This absorption cannot be attributed solely to synchrotron self-absorption; alternatively, free–free absorption due to thermal plasma is mainly at work in the spectrum. From combined perspectives, including mid-infrared and X-ray data, the AGN is obscured in a dense environment. The kinetic power of the nonthermal jet, as inferred from the extended emission, can play a more important role in dispersing the surrounding medium than the thermal outflow in IRAS F01004−2237. These findings hint that jet activities in ULIRGs may contribute to AGN feedback during galaxy evolution induced by merger events.

Ionised AGN outflows in the Goldfish galaxy: The illuminating and interacting red quasar eFEDSJ091157.4+014327 at z ∼ 0.6

Context. Evolutionary models suggest that the initial growth phases of active galactic nuclei (AGN) and their central supermassive black holes (SMBHs) are dust-enshrouded and characterised by jet or wind outflows that should gradually clear the interstellar medium (ISM) in the host by heating and/or expelling the surrounding gas. eFEDSJ091157.4+014327 (z ∼ 0.6) was selected from X-ray samples of eROSITA (extended ROentgen Survey with an Imaging Telescope Array) for its characteristics: red colours, X-ray obscuration (NH = 2.7 × 1022 cm−2) and luminous (LX = 6.5 × 1044 erg s−1), similar to those expected in quasars with outflows. It hosts an ionised outflow as revealed by a broad [O III]λ5007 Å emission line in the SDSS integrated spectrum. For a proper characterisation of the outflow properties and their effects, we need spatially resolved information. Aims. We aim to explore the environment around the red quasar, morphology of the [O III] gas and characterise the kinematics, mass outflow rates and energetics within the system. Methods. We used spatially resolved spectroscopic data from Multi Unit Spectroscopic Explorer (MUSE) with an average seeing of 0.6″ to construct flux, velocity and velocity dispersion maps. Thanks to the spatially resolved [O III]λ5007 Å emission detected, we provide insights into the morphology and kinematics of the ionised gas and better estimates of the outflow properties. Results. We find that the quasar is embedded in an interacting and merging system with three other galaxies ∼50 kpc from its nucleus. Spatially resolved kinematics reveal that the quasar has extended ionised outflows of up to 9.2−0.4+1.2 kpc with positive and negative velocities up to 1000 km s−1 and −1200 km s−1, respectively. The velocity dispersion (W80) ranges from 600–1800 km s−1. We associate the presence of high-velocity components with the outflow. The total mass outflow rate is estimated to be ∼10 M⊙ yr−1, a factor of ∼3–7 higher than the previous findings for the same target and kinetic power of 2 × 1042 erg s−1. Considering different AGN bolometric luminosities, the kinetic coupling efficiencies range from 0.01%–0.03% and the momentum boosts are ∼0.2. Conclusions. The kinetic coupling efficiency values are low, which indicates that the ionised outflow is not energetically relevant. These values don’t align with the theoretical predictions of both radiation-pressure-driven outflows and energy-conserving mechanisms. However, note that our results are based only on the ionised phase while theoretical predictions are multi-phase. Moreover, the mass loading factor of ∼5 is an indication that these outflows are more likely AGN-driven than star formation-driven.

A Rare, Strong Shock Front in the Merging Cluster SPT-CLJ 2031-4037

We present our findings from the new deep Chandra observations (256 ks) of the merging galaxy cluster SPT-CLJ 2031-4037 at z = 0.34. Our observations reveal intricate structures seen in a major merger akin to the Bullet Cluster. The X-ray data confirm the existence of two shock fronts, one to the northwest and one to the southeast, by directly measuring the temperature jump of gas across the surface brightness edges. The stronger shock front in the northwest has a density jump of 3.16 ± 0.34 across the sharp surface brightness edge and Mach number M=3.36−0.48+0.87 , which makes this cluster one of the rare merging systems with a Mach number M > 2. We use the northwestern shock to compare two models for shock heating—the instant heating model and the Coulomb collisional heating model—and we determine that the temperatures across the shock front agree with the Coulomb collisional model of heating. For the shock front in the southeastern region, we find a density jump of 1.53 ± 0.14 and a Mach number of M=1.36−0.08+0.09 .

Effects of galaxy environment on merger fraction

Aims. In this work we examine how environment influences the merger fraction, from the low density field environment to higher density groups and clusters. We also study how the properties of a group or cluster, as well as the position of a galaxy in the group or cluster, influences the merger fraction. Methods. We identified galaxy groups and clusters in the North Ecliptic Pole using a friends-of-friends algorithm and the local density. Once identified, we determined the central galaxies, group radii, velocity dispersions, and group masses of these groups and clusters. Merging systems were identified with a neural network as well as visually. With these identifications and properties of groups and clusters and merging galaxy identifications, we examined how the merger fraction changes as the local density changes for all galaxies as well as how the merger fraction changes as the properties of the groups or clusters change. Results. We find that the merger fraction increases as local density increases and decreases as the velocity dispersion increases, as is often found in the literature. A decrease in merger fraction as the group mass increases is also found. We also find that groups with larger radii have higher merger fractions. The number of galaxies in a group does not influence the merger fraction. Conclusions. The decrease in merger fraction as group mass increases is a result of the link between group mass and velocity dispersion. Hence, this decrease in merger fraction with increasing mass is a result of the decrease of merger fraction with velocity dispersion. The increasing relation between group radii and merger fraction may be a result of larger groups having smaller velocity dispersion at a larger distance from the centre or larger groups hosting smaller, infalling groups with more mergers. However, we do not find evidence of smaller groups having higher merger fractions.

A “MeerKAT-meets-LOFAR” study of the complex multi-component (mini-)halo in the extreme sloshing cluster Abell 2142

Context. Clusters of galaxies are known to be turbulent environments, whether they are merging systems where turbulence is injected via the conversion of gravitational potential energy into the intracluster medium (ICM), or whether they are relaxed systems in which small-scale core sloshing is occurring within the potential well. In many such systems, diffuse radio sources associated with the ICM are found: radio haloes and mini-haloes. Aims. Abell 2142 is a rich cluster undergoing an extreme episode of core sloshing, which has given rise to four cold fronts and a complex multi-component radio halo. Recent work revealed that there are three primary components to the halo that spans a distance of up to around 2.4 Mpc. The underlying physics of particle acceleration on these scales is poorly explored, and requires high-quality multi-frequency data with which to perform precision spectral investigation. We aim to perform such an investigation. Methods. We used new deep MeerKAT L-band (1283 MHz) observations in conjunction with LOFAR HBA (143 MHz) data as well as X-ray data from XMM-Newton and Chandra to study the spectrum of the halo and the connection between the thermal and non-thermal components of the ICM. Results. We confirm the presence of the third halo component, detecting it for the first time at 1283 MHz and confirming its ultra-steep spectrum nature, as we recovered an integrated spectrum of αH3, total = −1.68 ± 0.10. All halo components follow power-law spectra with increasingly steep spectra moving towards the cluster outskirts. We profiled the halo in three directions, finding evidence of asymmetry and spectral steepening along an axis perpendicular to the main axis of the cluster. Our investigation of the thermal non-thermal connection shows sub-linear correlations that are steeper at 1283 MHz than 143 MHz, and we find evidence of different connections in different components of the halo. In particular, we find both a moderate anti-correlation (H1, the core) and positive correlation (H2, the ridge) between the radio spectral index and X-ray temperature. Conclusions. Our results are broadly consistent with an interpretation of turbulent (re-)acceleration following an historic minor cluster merger scenario in which we must invoke some inhomogeneities. However, the anti-correlation between the radio spectral index and X-ray temperature in the cluster core is more challenging to explain; the presence of three cold fronts and a generally lower temperature may provide the foundations of an explanation, but detailed modelling is required to study this further.

Hyperspectral image classification based on superpixel merging and broad learning system

AbstractMost spectral–spatial classification methods for hyperspectral images (HSIs) can achieve satisfactory classification results. However, the common problem faced with these approaches is the need for a long training time and sufficient training samples. To address this issue, this study proposes an effective spectral–spatial HSI classification method based on superpixel merging, superpixel smoothing and broad learning system (SMS‐BLS). The newly introduced parameter‐free superpixel merging technique based on local modularity not only enhances the role of local spatial information in classification, but also maintains class boundary information as much as possible. In addition, the spectral and spatial information of HSIs is further fused during the superpixel smoothing process. As a result, with limited training samples, using merged and smoothed superpixels instead of pixels as input to the broad learning system significantly improves its classification performance. Moreover, the merged superpixels weaken the dependence of the classification results on the superpixel segmentation scale. The effectiveness of the proposed method was validated on three HSI benchmarks, namely Indian Pines, Pavia University and Salinas. Experimental and comparative results show the superiority of the method to other state‐of‐the‐art approaches in terms of overall accuracy and running time.

Distinguishing ΛCDM from Evolving Dark Energy with Om Two-point Statistics: Implications from the Space-borne Gravitational-wave Detector

The Omh 2(z i , z j ) two-point diagnostics was proposed as a litmus test of the ΛCDM model, and measurements of the cosmic expansion rate H(z) have been extensively used to perform this test. The results obtained so far suggested a tension between observations and predictions of the ΛCDM model. However, the data set of H(z) direct measurements from cosmic chronometers and baryon acoustic oscillations was quite limited. This motivated us to study the performance of this test on a larger sample obtained in an alternative way. In this paper, we propose that gravitational-wave (GW) standard sirens could provide large samples of H(z) measurements in the redshift range of 0 < z < 5, based on the measurements of the dipole anisotropy of luminosity distance arising from the matter inhomogeneities of the large-scale structure and the local motion of the observer. We discuss the effectiveness of our method in the context of the space-borne DECi-herz Interferometer Gravitational-wave Observatory, based on a comprehensive H(z) simulated data set from binary neutron star merger systems. Our results indicate that in the GW domain, the Omh 2(z i , z j ) two-point diagnostics could effectively distinguish whether ΛCDM is the best description of our Universe. We also discuss the potential of our methodology in determining possible evidence for dark energy evolution, focusing on its performance on the constant and redshift-dependent dark energy equation of state.

Study of the $ 50$ kpc circumgalactic environment around the merger system J2057-0030 at $ z $ sim 4.6 using ALMA

We present ALMA band-7 observations of J2057-0030, a multi-component merger system at $z$ sim 4.68 spanning at least 50 kpc in size, using the C$ ii lambda 157.74 mu m line and underlying far-infrared (FIR) continuum. We find two main components, the quasar (QSO) and a dusty star-forming galaxy (DSFG), both detected in C$ ii and continuum emission as well as multiple neighboring clumps detected only in C$ ii . Three of these clumps form a (tidal) tail that extends from the QSO in a straight direction to the west, covering a projected distance of sim 10 kpc. This perturbed morphology, added to a spatial distance of sim 20 kpc and a velocity offset of $ v $ = 68 km s$^ $ between the QSO and the DSFG, strongly supports a merging scenario. By fitting a spectral energy distribution model to the continuum data, we estimate star formation rates of approx 402 $M_ odot $ yr$^ $ for the QSO host and approx 244 $M_ odot $ yr$^ $ for the DSFG, which locate them on or close to the main sequence of star-forming galaxies. The J2057-0030 QSO was selected for being one of the brightest unobscured quasars at its redshift while presenting a rather modest star formation rate. Based on a commonly accepted paradigm regarding the formation of quasars, this result is expected for a quasar that has already passed an obscured phase of rapid star formation during a major merger. However, we see that the merger event in this system is far from being finished, and it is rather likely somewhere between the first pericenter and subsequent close passages. This is presumably another case of a high-$z$ quasar residing in a high-density environment with a companion obscured galaxy.