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We report the discovery of a binary galaxy cluster merger via a search of the redMaPPer optical cluster catalog, with a projected separation of 535 kpc between the brightest cluster galaxies (BCGs). Archival XMM-Newton spectro-imaging reveals a gas peak between the BCGs, suggesting a recent pericenter passage. We conduct a galaxy redshift survey to quantify the line-of-sight velocity difference (153 ± 281 km s ^−1 ) between the two subclusters. We present weak-lensing mass maps from archival Hubble Space Telescope Advanced Camera for Surveys (HST/ACS) imaging, revealing masses of M _200 = 4.5 ± 0.8 × 10 ^14 and 2.8 ± 0.7 × 10 ^14 M _⊙ associated with the southern and northern galaxy subclusters, respectively. We also present deep GMRT 650 MHz data revealing extended emission, 420 kpc long, which may be an active galactic nucleus (AGN) tail but is potentially also a candidate radio relic. We draw from cosmological n -body simulations to find analog systems, which imply that this system is observed fairly soon (60–271 Myr) after pericenter, and that the subcluster separation vector is within 22° of the plane of the sky, making it suitable for an estimate of the dark matter scattering cross section. We find $\tfrac{{\sigma }_{\mathrm{DM}}}{m}=1.1\pm 0.6$ cm ^2 g ^−1 , suggesting that further study of this system could support interestingly tight constraints.

A dissociative merger is formed by the interplay of ram pressure and gravitational forces, which can lead to a spatial displacement of the dark matter and baryonic components of the recently collided subclusters. CIZA J0107.7+5408 is a nearby ( z = 0.105) dissociative merger that hosts two X-ray brightness peaks and a bimodal galaxy distribution. Analyzing MMT/Hectospec observations, we investigate the line-of-sight and spatial distribution of cluster galaxies. Utilizing deep, high-resolution Hubble Space Telescope Advanced Camera for Surveys imaging and large field-of-view Subaru Hyper-Suprime-Cam observations, we perform a weak-lensing analysis of CIZA J0107.7+5408. Our weak-lensing analysis detects a bimodal mass distribution that is spatially consistent with the cluster galaxies but significantly offset from the X-ray brightness peaks. Fitting two Navarro–Frenk–White halos to the lensing signal, we find an equal-mass merger with subcluster masses of ${M}_{200,\mathrm{NE}}={2.8}_{-1.1}^{+1.1}\times {10}^{14}$ M _⊙ and ${M}_{200,{SW}}={3.1}_{-1.2}^{+1.2}\times {10}^{14}$ M _⊙ . Moreover, the mass-to-light ratios of the subclusters, ${(M/L)}_{\mathrm{NE}}={571}_{-91}^{+89}\ {M}_{\odot }/{L}_{\odot ,B}$ and ${(M/L)}_{\mathrm{SW}}={564}_{-89}^{+87}\ {M}_{\odot }/{L}_{\odot ,B}$ , are found to be consistent with each other and within the range of mass-to-light ratios found for galaxy clusters.

We present high-resolution (∼1″), 1.5 GHz continuum observations of the brightest cluster galaxies (BCGs) of 13 CLASH (Cluster Lensing And Supernova survey with Hubble) clusters at with the Karl G. Jansky Very Large Array (JVLA). Radio emission is clearly detected and characterized for 11 BCGs, while for two of them we obtain only upper limits to their radio flux ( mJy at 5σ confidence level). We also consider five additional clusters whose BCG is detected in FIRST or NVSS. We find radio powers in the range from to and radio spectral indices (defined as the slope between 1.5 and 30 GHz) distributed from to −0.25 around the central value . The radio emission from the BCGs is resolved in three cases (Abell 383, MACS J1931, and RX J2129), and unresolved or marginally resolved in the remaining eight cases observed with JVLA. In all the cases the BCGs are consistent with being powered by active galactic nuclei. The radio power shows a positive correlation with the BCG star formation rate, and a negative correlation with the central entropy of the surrounding intracluster medium (ICM) except in two cases (MACS J1206 and CL J1226). Finally, over the restricted range in radio power sampled by the CLASH BCGs, we observe a significant scatter between the radio power and the average mechanical power stored in the ICM cavities. [ABSTRACT FROM AUTHOR]

We present an analysis of the merging cluster MACS J1149.5+2223 using archival imaging from Subaru/Suprime-Cam and multi-object spectroscopy from Keck/DEIMOS and Gemini/GMOS. We employ two- and three-dimensional substructure tests and determine that MACS J1149.5+2223 is composed of two separate mergers among three subclusters occurring ∼1 Gyr apart. The primary merger gives rise to elongated X-ray morphology and a radio relic in the southeast. The brightest cluster galaxy is a member of the northern subcluster of the primary merger. This subcluster is very massive (). The southern subcluster is also very massive (), yet it lacks an associated X-ray surface brightness peak, and it has been unidentified previously despite the detailed study of this Frontier Field cluster. A secondary merger is occurring in the north along the line of sight (LOS) with a third, less massive subcluster (). We perform a Monte Carlo dynamical analysis on the main merger and estimate a collision speed at pericenter of km s−1. We show the merger to be returning from apocenter with core passage occurring Gyr before the observed state. We identify the LOS merging subcluster in a strong lensing analysis in the literature and show that it is likely bound to MACS J1149 despite having reached an extreme collision velocity of ∼4000 km s−1. [ABSTRACT FROM AUTHOR]

Abell 1142 is a low-mass galaxy cluster at low redshift containing two comparable brightest cluster galaxies (BCGs) resembling a scaled-down version of the Coma Cluster. Our Chandra analysis reveals an X-ray emission peak, roughly 100 kpc away from either BCG, which we identify as the cluster center. The emission center manifests itself as a second beta-model surface brightness component distinct from that of the cluster on larger scales. The center is also substantially cooler and more metal-rich than the surrounding intracluster medium (ICM), which makes Abell 1142 appear to be a cool-core cluster. The redshift distribution of its member galaxies indicates that Abell 1142 may contain two subclusters, each of which contain one BCG. The BCGs are merging at a relative velocity of ≈1200 km s−1. This ongoing merger may have shock-heated the ICM from ≈2 keV to above 3 keV, which would explain the anomalous LX–TX scaling relation for this system. This merger may have displaced the metal-enriched “cool core” of either of the subclusters from the BCG. The southern BCG consists of three individual galaxies residing within a radius of 5 kpc in projection. These galaxies should rapidly sink into the subcluster center due to the dynamical friction of a cuspy cold dark matter halo. [ABSTRACT FROM AUTHOR]