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Magnetic fields in the intracluster medium affect the structure and the evolution of galaxy clusters. However, their properties are largely unknown, and measuring magnetic fields in galaxy clusters is challenging, especially on large scales outside of individual radio sources. In this work, we probe the plane-of-the-sky orientation of magnetic fields in clusters using the intensity gradients. The technique is a branch of the gradient technique (GT) that employs emission intensity maps from turbulent gas. We utilize Chandra X-ray images of the Perseus, M87, Coma, and A2597 galaxy clusters, and the VLA radio observations of the synchrotron emission from Perseus. We find that the fields predominantly follow the sloshing arms in Perseus, which is in agreement with numerical simulations. The GT-predicted magnetic field shows signatures of magnetic draping around rising bubbles driven by supermassive black hole feedback in the centers of cool-core clusters, as well as draping around substructures merging with the Coma cluster. We calculate the mean-field orientation with respect to the radial direction in these clusters. In the central regions of cool-core clusters, the mean orientation of the magnetic fields is preferentially azimuthal. There is broad agreement between the magnetic field of Perseus predicted using the X-ray and radio data. Further numerical studies and better future observations with higher resolution and larger effective area will help reduce the uncertainties of this method. [ABSTRACT FROM AUTHOR]

We present new Chandra observations of A2199 that show evidence of gas sloshing due to a minor merger, as well as impacts of the radio source, 3C 338, hosted by the central galaxy, NGC 6166, on the intracluster gas. The new data are consistent with previous evidence of a Mach ≃ 1.46 shock 100″ from the cluster center, although there is still no convincing evidence for the expected temperature jump. Other interpretations of this feature are possible, but none is fully satisfactory. Large scale asymmetries, including enhanced X-ray emission 200″ southwest of the cluster center and a plume of low entropy, enriched gas reaching 50″ to the north of the center, are signatures of gas sloshing induced by core passage of a merging subcluster about 400 Myr ago. An association between the unusual radio ridge and low entropy gas are consistent with this feature being the remnant of a former radio jet that was swept away from the active galactic nucleus by gas sloshing. A large discrepancy between the energy required to produce the 100″ shock and the enthalpy of the outer radio lobes of 3C 338 suggests that the lobes were formed by a more recent, less powerful radio outburst. The lack of evidence for shocks in the central 10″ indicates that the power of the jet now is some two orders of magnitude smaller than when the 100″ shock was formed. [ABSTRACT FROM AUTHOR]

Chandra x-ray observations of NGC 4342, a low-stellar mass (MK = –22.79 mag) early-type galaxy, show luminous, diffuse x-ray emission originating from hot gas with temperature of kT ∼ 0.6 keV. The observed 0.5-2 keV band luminosity of the diffuse x-ray emission within the D25 ellipse is L0.5-2 keV = 2.7 × 1039 erg s–1. The hot gas has a significantly broader distribution than the stellar light, and shows strong hydrodynamic disturbances with a sharp surface brightness edge to the northeast and a trailing tail. We identify the edge as a cold front and conclude that the distorted morphology of the hot gas is produced by ram pressure as NGC 4342 moves through external gas. From the thermal pressure ratios inside and outside the cold front, we estimate the velocity of NGC 4342 and find that it moves supersonically (M ∼ 2.6) toward the northeast. Outside the optical extent of the galaxy, we detect ∼17 bright () excess x-ray point sources. The excess sources are presumably LMXBs located in metal-poor globular clusters (GCs) in the extended dark matter halo of NGC 4342. Based on the number of excess sources and the average frequency of bright LMXBs in GCs, we estimate that NGC 4342 may host roughly 850-1700 GCs. In good agreement with this, optical observations hint that NGC 4342 may harbor 1200 ± 500 GCs. This number corresponds to a GC specific frequency of SN = 19.9 ± 8.3, which is among the largest values observed in full-size galaxies. [ABSTRACT FROM AUTHOR]

We study two nearby early-type galaxies, NGC 4342 and NGC 4291, that host unusually massive black holes relative to their low stellar mass. The observed black-hole-to-bulge mass ratios of NGC 4342 and NGC 4291 are 6.9+3.8– 2.3% and 1.9% ± 0.6%, respectively, which significantly exceed the typical observed ratio of ∼0.2%. As a consequence of the exceedingly large black-hole-to-bulge mass ratios, NGC 4342 and NGC 4291 are ≈5.1σ and ≈3.4σ outliers from the M•-Mbulge scaling relation, respectively. In this paper, we explore the origin of the unusually high black-hole-to-bulge mass ratio. Based on Chandra X-ray observations of the hot gas content of NGC 4342 and NGC 4291, we compute gravitating mass profiles, and conclude that both galaxies reside in massive dark matter halos, which extend well beyond the stellar light. The presence of dark matter halos around NGC 4342 and NGC 4291 and a deep optical image of the environment of NGC 4342 indicate that tidal stripping, in which ≳ 90% of the stellar mass was lost, cannot explain the observed high black-hole-to-bulge mass ratios. Therefore, we conclude that these galaxies formed with low stellar masses, implying that the bulge and black hole did not grow in tandem. We also find that the black hole mass correlates well with the properties of the dark matter halo, suggesting that dark matter halos may play a major role in regulating the growth of the supermassive black holes. [ABSTRACT FROM AUTHOR]