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Register a new userChandra Observations of the Spectacular A3411-12 Merger Event
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Felipe Andrade-Santos
Publication date
2019
fields
Physics
and research's language is
English
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We present deep Chandra observations of A3411-12, a remarkable merging cluster that hosts the most compelling evidence for electron re-acceleration at cluster shocks to date. Using the $Y_X-M$ scaling relation, we find $r_{500} sim 1.3$ Mpc, $M_{500} = (7.1 pm 0.7) times 10^{14} M_{rm{odot}}$, $kT=6.5pm 0.1$ keV, and a gas mass of $M_{rm g,500} = (9.7 pm 0.1) times 10^{13} M_odot$. The gas mass fraction within $r_{500}$ is $f_{rm g} = 0.14 pm 0.01$. We compute the shock strength using density jumps to conclude that the Mach number of the merging subcluster is small ($M leq 1.15_{-0.09}^{+0.14}$). We also present pseudo-density, projected temperature, pseudo-pressure, and pseudo-entropy maps. Based on the pseudo-entropy map we conclude that the cluster is undergoing a mild merger, consistent with the small Mach number. On the other hand, radio relics extend over Mpc scale in the A3411-12 system, which strongly suggests that a population of energetic electrons already existed over extended regions of the cluster.
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The HST Frontier Fields cluster MACS J1149.6+2223 is one of the most complex merging clusters, believed to consist of four dark matter halos. We present results from deep (365 ks) Chandra observations of the cluster, which reveal the most distant cold front (z=0.544) discovered to date. In the cluster outskirts, we also detect hints of a surface brightness edge that could be the bow shock preceding the cold front. The substructure analysis of the cluster identified several components with large relative radial velocities, thus indicating that at least some collisions occur almost along the line of sight. The inclination of the mergers with respect to the plane of the sky poses significant observational challenges at X-ray wavelengths. MACS J1149.6+2223 possibly hosts a steep-spectrum radio halo. If the steepness of the radio halo is confirmed, then the radio spectrum, combined with the relatively regular ICM morphology, could indicate that MACS J1149.6+2223 is an old merging cluster.
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