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We study a merger of the NGC 4839 group with the Coma cluster using X-ray observations from the XMM-Newton and Chandra telescopes. X-ray data show two prominent features: (i) a long (~600 kpc in projection) and bent tail of cool gas trailing (towards south-west) the optical center of NGC 4839, and ii) a sheath region of enhanced X-ray surface brightness enveloping the group, which is due to hotter gas. While at first glance the X-ray images suggest that we are witnessing the first infall of NGC 4839 into the Coma cluster core, we argue that a post-merger scenario provides a better explanation of the observed features and illustrate this with a series of numerical simulations. In this scenario, the tail is formed when the group, initially moving to the south-west, reverses its radial velocity after crossing the apocenter, the ram pressure ceases and the ram-pressure-displaced gas falls back toward the center of the group and overshoots it. Shortly after the apocenter passage, the optical galaxy, dark matter and gaseous core move in a north-east direction, while the displaced gas continues moving to the south-west. The sheath is explained as being due to interaction of the re-infalling group with its own tail of stripped gas mixed with the Coma gas. In this scenario, the shock, driven by the group before reaching the apocenter, has already detached from the group and would be located close to the famous relic to the south-west of the Coma cluster.
We evaluate the dry merger activity in the Coma cluster, using a spectroscopically complete sample of 70 red-sequence (RS) galaxies, most of which (~75%) are located within 0.2R200 (~0.5 Mpc) from the cluster center, with data from the Coma Treasury
We present deep Chandra, XMM-Newton, Giant Metrewave Radio Telescope and Halpha observations of the group-group merger NGC 6338. X-ray imaging and spectral mapping show that as well as trailing tails of cool, enriched gas, the two cool cores are embe
One possible channel for the formation of dwarf galaxies involves birth in the tidal tails of interacting galaxies. We report the detection of a bright UV tidal tail and several young tidal dwarf galaxy candidates in the post-merger galaxy NGC 4922 i
This is the first paper in a series of studies of the Coma cluster using the SRG/eROSITA X-ray data obtained in course of the Calibration and Performance Verification observations. The data cover $sim3^circtimes 3^circ$ area around the cluster with a
Based on Suzaku X-ray observations, we study the hot gas around the NGC4839 group of galaxies and the radio relic in the outskirts of the Coma cluster. We find a gradual decline in the gas temperature from 5 keV around NGC4839 to 3.6 keV at the radio