The environmental influence of cluster media on its member galaxies, known as Butcher–Oemler effect, has recently been subject to revision due to numerous observations of strong morphological ...transformations occurring outside the cluster virial radii, caused by some unidentified gas removal processes. In this context we present new XMM-Newton observations of M 86 group. The unique combination of high spatial and spectral resolution and large field of view of XMM-Newton allows an in-depth investigation of the processes involved in the spectacular disruption of this object. We identify a possible shock with Mach number of ~1.4 in the process of crushing the galaxy in the North-East direction. The latter is ascribed to the presence of a dense X-ray emitting filament, previously revealed in the RASS data. The shock is not associated with other previously identified features of M 86 X-ray emission, such as the plume, the north-eastern arm and the southern extension, which are found to have low entropy, similar to the inner 2 kpc of M 86. Finally, mere existence of the large scale gas halo around the M 86 group, suggests that the disruptions of M 86's X-ray halo may be caused by small-scale types of interactions such as galaxy-galaxy collisions.
Using a mosaic of nine XMM-Newton observations, we study the hydrodynamic state of the merging cluster of galaxies Abell 3266. The high signal-to-noise ratio of spectroscopic data of XMM-Newton ...allows us to determine the thermodynamic conditions of the intracluster medium on 650 kpc scales. High statistical quality X-ray data reveal the presence of an extended region of low-entropy gas (LEG) running northeast from the primary cluster core along the nominal merger axis. The LEG is a major feature distinguishing the merger event in A3266 from other clusters. The mass of the low-entropy gas is 61.3 x 10 super(13) M sub(z). We test the possibility that the origin of the observed low-entropy gas is related either to the disruption of a preexisting cooling core in Abell 3266 or to the stripping of gas from an infalling subcluster. We find that the low-entropy gas has a metallicity 1.5-2 times higher than the bulk of the cluster, yet lower than one-half the solar value typical for the cool cores. In addition, both the radial pressure and entropy profiles, as well as the iron abundance of Abell 3266, do not resemble those in other known cool core clusters (e.g., Abell 478). Thus, we conclude that our observations favor a scenario in which the low-entropy region corresponds to subcluster gas stripped from its dark matter halo. In this scenario the subcluster would be falling onto the core of A3266 from the foreground, having a velocity component in the observer plane toward the southwest. The arguments based on both velocity dispersion and gas mass measurements suggest a mass ratio in the merger of 1:10.
We investigate numerically the contribution to the cosmic gamma-ray background from cosmic-ray ions and electrons accelerated at intergalactic shocks associated with cosmological structure formation. ...We show that the kinetic energy of accretion flows in the low-redshift intergalactic medium is thermalized primarily through moderately strong shocks, which allow for an efficient conversion of shock ram pressure into cosmic-ray pressure. Cosmic rays accelerated at these shocks produce a diffuse gamma-ray flux which is dominated by inverse Compton emission from electrons scattering off cosmic microwave background photons. Decay of neutral π mesons generated in p—p inelastic collisions of the ionic cosmic-ray component with the thermal gas contribute about 30 per cent of the computed emission. Based on experimental upper limits on the photon flux above 100 MeV from nearby clusters we constrain the efficiency of conversion of shock ram pressure into relativistic CR electrons to ≲1 per cent. Thus, we find that cosmic rays of cosmological origin can generate an overall significant fraction of order 20 per cent and no more than 30 per cent of the measured gamma-ray background.
This paper describes a model of electron energization and cyclotron-maser emission applicable to astrophysical magnetized collisionless shocks. It is motivated by the work of Begelman, Ergun and Rees ...Astrophys. J.
625
, 51 (2005) who argued that the cyclotron-maser instability occurs in localized magnetized collisionless shocks such as those expected in blazar jets. We report on recent research carried out to investigate electron acceleration at collisionless shocks and maser radiation associated with the accelerated electrons. We describe how electrons accelerated by lower-hybrid waves at collisionless shocks generate cyclotron-maser radiation when the accelerated electrons move into regions of stronger magnetic fields. The electrons are accelerated along the magnetic field and magnetically compressed leading to the formation of an electron velocity distribution having a horseshoe shape due to conservation of the electron magnetic moment. Under certain conditions the horseshoe electron velocity distribution function is unstable to the cyclotron-maser instability Bingham and Cairns, Phys. Plasmas
7
, 3089 (2000); Melrose, Rev. Mod. Plasma Phys.
1
, 5 (2017).
We present COSMOCR, a numerical code for the investigation of cosmic ray related studies in computational cosmology. The code follows the diffusive shock acceleration, the mechanical and radiative ...energy losses and the spatial transport of the supra-thermal particles in cosmic environment. Primary cosmic ray electrons and ions are injected at shocks according to the thermal leakage prescription. Secondary electrons are continuously injected as a results of p-p inelastic collisions of primary cosmic ray ions and thermal background nuclei. The code consists of a conservative, finite volume method with a power-law sub-grid model in momentum space. Two slightly different schemes are implemented depending on the stiffness of the cooling terms. Comparisons of numerical results with analytical solution for a number of tests of direct interest show remarkable performance of the present code.
We present an observational study of the LX vs. $L_{\rm B} \sigma^2$ relation for early-type galaxies in the Coma cluster based on the XMM-Newton survey data. Compared to a similar relation for a ...sample dominated by field early-type galaxies, the Coma cluster galaxies show a flatter slope. Our calculations show that adiabatic compression produces a flattening in the LX vs. $L_{\rm B}\sigma^2$ relation that is in remarkable agreement with the observed effect. Our scenario is further supported by the observed compactness of the X-ray emission of Coma galaxies.
There is now firm evidence that the intracluster medium (ICM) consists of a mixture of hot plasma, magnetic fields and relativistic particles. The most important evidence for non-thermal phenomena in ...galaxy clusters comes from the spectacular synchrotron radio emission diffused over Mpc scales observed in a growing number of massive clusters and, more recently, in the hard X-ray tails detected in a few cases in excess of the thermal bremsstrahlung spectrum. A promising possibility to explain giant radio haloes is given by the presence of relativistic electrons reaccelerated by some kind of turbulence generated in the cluster volume during merger events. With the aim of investigating the connection between thermal and non-thermal properties of the ICM, in this paper we develop a statistical magneto-turbulent model which describes in a self-consistent way the evolution of the thermal ICM and that of the non-thermal emission from clusters. Making use of the extended Press–Schechter formalism, we follow cluster mergers and estimate the injection rate of the fluid turbulence generated during these energetic events. We then calculate the evolution of the spectrum of the relativistic electrons in the ICM during the cluster life by taking into account both the electron acceleration due to the merger-driven turbulence and the relevant energy losses of the electrons. We end up with a synthetic population of galaxy clusters for which the evolution of the ICM and of the non-thermal spectrum emitted by the accelerated electrons is calculated. The generation of detectable non-thermal radio and hard X-ray emission in the simulated clusters is found to be possible during major merger events for reliable values of the model parameters. In addition the occurrence of radio haloes as a function of the mass of the parent clusters is calculated and compared with observations. In this case it is found that the model expectations are in good agreement with observations: radio haloes are found in about 30 per cent of the more massive clusters in our synthetic population (M≳ 1.8 × 1015 M⊙) and in about 4 per cent of the intermediate massive clusters (9 × 1014 < M < 1.8 × 1015 M⊙), while the radio halo phenomenon is found to be extremely rare in the case of the smaller clusters.
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