ABSTRACT
We present detailed spatially resolved measurements of the thermodynamic properties of the X‐ray‐emitting gas in the inner regions of the five nearest, X‐ray and optically brightest, and ...most X‐ray morphologically relaxed giant elliptical galaxies known. Beyond the innermost region at r ≳ 1 kpc, and out to r ∼ 6 kpc, the density, pressure, entropy and cooling time distributions for the X‐ray‐emitting gas follow remarkably similar, simple, power‐law‐like distributions. Notably, the entropy profiles follow a form K ∝ rα, with an index α = 0.92–1.07. The cumulative hot X‐ray‐emitting gas mass profiles and the gas mass to stellar light ratios of all five galaxies are also similar. Overall the observed similarity of the thermodynamic profiles in this radial range argues that, in these systems, relativistic jets heat the gas at a similar rate averaged over time‐scales longer than the cooling time tcool ≳ 108 yr. These jets are powered by accretion from the hot gas, or material entrained within it, on to the central supermassive black hole. This jet heating creates an energy balance where heating and cooling are in equilibrium, keeping the hot galactic atmospheres in a ‘steady state’. Within r ≲ 1 kpc, this similarity breaks down: the observed entropy profiles show well‐resolved flattening and the values differ from system to system substantially. The accretion rate on to the black hole and the active galactic nucleus activity, heating the interstellar medium, must therefore vary significantly on time‐scales shorter than tcool = 107–108 yr.
ABSTRACT We present the first measurements of the abundances of -elements (Mg, Si, and S) extending out beyond the virial radius of a cluster of galaxies. Our results, based on Suzaku Key Project ...observations of the Virgo Cluster, show that the chemical composition of the intracluster medium is consistent with being constant on large scales, with a flat distribution of the Si/Fe, S/Fe, and Mg/Fe ratios as a function of radius and azimuth out to 1.4 Mpc (1.3 r200). Chemical enrichment of the intergalactic medium due solely to core-collapse supernovae (SNcc) is excluded with very high significance; instead, the measured metal abundance ratios are generally consistent with the solar value. The uniform metal abundance ratios observed today are likely the result of an early phase of enrichment and mixing, with both SNcc and SNe Ia contributing to the metal budget during the period of peak star formation activity at redshifts of 2-3. We estimate the ratio between the number of SNe Ia and the total number of supernovae enriching the intergalactic medium to be between 12% and 37%, broadly consistent with the metal abundance patterns in our own Galaxy or with the SN Ia contribution estimated for the cluster cores.
The Beautiful Mess in Abell 2255 Botteon, A.; Brunetti, G.; van Weeren, R. J. ...
Astrophysical journal/The Astrophysical journal,
07/2020, Volume:
897, Issue:
1
Journal Article
Peer reviewed
Open access
We present LOFAR observations of one of the most spectacular objects in the radio sky: Abell 2255. This is a nearby (z = 0.0806) merging galaxy cluster hosting one of the first radio halos ever ...detected in the intracluster medium (ICM). The deep LOFAR images at 144 MHz of the central ∼10 Mpc2 region show a plethora of emission on different scales, from tens of kiloparsecs to above megaparsec sizes. In this work, we focus on the innermost region of the cluster. Among the numerous interesting features observed, we discover remarkable bright and filamentary structures embedded in the radio halo. We incorporate archival WSRT 1.2 GHz data to study the spectral properties of the diffuse synchrotron emission and find a very complex spectral index distribution in the halo spanning a wide range of values. We combine the radio data with Chandra observations to investigate the connection between the thermal and nonthermal components by quantitatively comparing the radio and X-ray surface brightness and the spectral index of the radio emission with the thermodynamical quantities of the ICM. Despite the multitude of structures observed in the radio halo, we find that the X-ray and radio emission are overall well correlated. The fact that the steepest spectrum emission is located in the cluster center and traces regions with high entropy possibly suggests the presence of seed particles injected by radio galaxies that are spread in the ICM by the turbulence generating the extended radio halo.
We present Suzaku observations of the Centaurus cluster out to 0.95r
200, taken along a strip to the north-west. We have also used congruent Chandra observations of the outskirts to resolve point ...sources down to a threshold flux around seven times lower than that achievable with just Suzaku data, considerably reducing the systematic uncertainties in the cosmic X-ray background emission in the outskirts. We find that the temperature decreases by a factor of 2 from the peak temperature to the outskirts. The entropy profile demonstrates a central excess (within 0.5r
200) over the baseline entropy profile predicted by simulations of purely gravitational hierarchical structure formation. In the outskirts, the entropy profile is in reasonable agreement with the baseline entropy profile from Voit et al. but lies slightly below it. We find that the pressure profile agrees with the universal pressure profile of Arnaud et al. but lies slightly above it in the outskirts. The excess pressure and decrement in entropy in the outskirts appear to be the result of an excess in the measured gas density, possible due to gas clumping biasing the density measurements high. The gas mass fraction rises and reaches the mean cosmic baryon fraction at the largest radius studied. The clumping-corrected gas mass fraction agrees with the expected hot gas fraction and with the simulations of Young et al. We further the analysis of Walker et al. which studied the shapes of the entropy profiles of the clusters so far explored in the outskirts with Suzaku. When scaled by the self-similar entropy, the Suzaku entropy profiles demonstrate a central excess over the baseline entropy profile, and are consistent with it at around r
500. However, outside r
500 the entropy profiles tend to lie below the baseline entropy profile.
We present the results of a very deep (500 ks) Chandra observation, along with tailored numerical simulations, of the nearest, best resolved cluster cold front in the sky, which lies 90 kpc (19 ...arcmin) to the north-west of M87. The northern part of the front appears the sharpest, with a width smaller than 2.5 kpc (1.5 Coulomb mean free paths; at 99 per cent confidence). Everywhere along the front, the temperature discontinuity is narrower than 4-8 kpc and the metallicity gradient is narrower than 6 kpc, indicating that diffusion, conduction and mixing are suppressed across the interface. Such transport processes can be naturally suppressed by magnetic fields aligned with the cold front. Interestingly, comparison to magnetohydrodynamic simulations indicates that in order to maintain the observed sharp density and temperature discontinuities, conduction must also be suppressed along the magnetic field lines. However, the northwestern part of the cold front is observed to have a non-zero width. While other explanations are possible, the broadening is consistent with the presence of Kelvin-Helmholtz instabilities (KHI) on length-scales of a few kpc. Based on comparison with simulations, the presence of KHI would imply that the effective viscosity of the intracluster medium is suppressed by more than an order of magnitude with respect to the isotropic Spitzer-like temperature dependent viscosity. Underneath the cold front, we observe quasi-linear features that are approximately 10 per cent brighter than the surrounding gas and are separated by approximately 15 kpc from each other in projection. Comparison to tailored numerical simulations suggests that the observed phenomena may be due to the amplification of magnetic fields by gas sloshing in wide layers below the cold front, where the magnetic pressure reaches approximately 5-10 per cent of the thermal pressure, reducing the gas density between the bright features.
We perform hydrodynamical simulations of minor-merger-induced gas sloshing and the subsequent formation of cold fronts in the Virgo cluster. Comparing to observations, we show for the first time that ...the sloshing scenario can reproduce the radii and the contrasts in X-ray brightness, projected temperature and metallicity across the cold fronts quantitatively. The comparison suggests a third cold front 20 kpc north-west of the Virgo core. We identify several new features typical for sloshing cold fronts: an alternating distribution of cool, metal-enriched X-ray brightness excess regions and warm brightness deficit regions of reduced metallicity; a constant or radially decreasing temperature accompanied by a plateau in metallicity inside the cold fronts; a warm rim outside the cold fronts and a large-scale brightness asymmetry. We can trace these new features not only in Virgo, but also in other clusters exhibiting sloshing cold fronts. By comparing synthetic and real observations, we estimate that the original minor-merger event took place about 1.5 Gyr ago when a subcluster of 1-4 × 1013 M⊙ passed the Virgo core at 100-400 kpc distance, where a smaller mass corresponds to a smaller pericentre distance, and vice versa. From our inferred merger geometry, we derive the current location of the disturbing subcluster to be about 1-2 Mpc east of the Virgo core. A possible candidate is M60. Additionally, we quantify the metal redistribution by sloshing and discuss its importance. We verify that the subcluster required to produce the observed cold fronts could be completely ram-pressure-stripped before reaching the Virgo centre, and discuss the conditions required for this to be achieved. Finally, we demonstrate that the bow shock of a fast galaxy passing the Virgo cluster at ∼400 kpc distance also causes sloshing and leads to very similar cold front structures. The responsible galaxy would be located about 2 Mpc north of the Virgo centre. A possible candidate is M85.
ABSTRACT We present deep LOFAR observations between 120 and 181 MHz of the "Toothbrush" (RX J0603.3+4214), a cluster that contains one of the brightest radio relic sources known. Our LOFAR ...observations exploit a new and novel calibration scheme to probe 10 times deeper than any previous study in this relatively unexplored part of the spectrum. The LOFAR observations, when combined with VLA, GMRT, and Chandra X-ray data, provide new information about the nature of cluster merger shocks and their role in re-accelerating relativistic particles. We derive a spectral index of at the northern edge of the main radio relic, steepening toward the south to . The spectral index of the radio halo is remarkably uniform ( , with an intrinsic scatter of ). The observed radio relic spectral index gives a Mach number of , assuming diffusive shock acceleration. However, the gas density jump at the northern edge of the large radio relic implies a much weaker shock ( , with an upper limit of ). The discrepancy between the Mach numbers calculated from the radio and X-rays can be explained if either (i) the relic traces a complex shock surface along the line of sight, or (ii) if the radio relic emission is produced by a re-accelerated population of fossil particles from a radio galaxy. Our results highlight the need for additional theoretical work and numerical simulations of particle acceleration and re-acceleration at cluster merger shocks.
THERMODYNAMICS OF THE COMA CLUSTER OUTSKIRTS Simionescu, A; Werner, N; Urban, O ...
Astrophysical journal/The Astrophysical journal,
09/2013, Volume:
775, Issue:
1
Journal Article
Peer reviewed
Open access
We present results from a large mosaic of Suzaku observations of the Coma Cluster, the nearest and X-ray brightest hot (~8 keV), dynamically active, non-cool core system, focusing on the ...thermodynamic properties of the intracluster medium on large scales. For azimuths not aligned with an infalling subcluster toward the southwest, our measured temperature and X-ray brightness profiles exhibit broadly consistent radial trends, with the temperature decreasing from about 8.5 keV at the cluster center to about 2 keV at a radius of 2 Mpc, which is the edge of our detection limit. The southwest merger significantly boosts the surface brightness, allowing us to detect X-ray emission out to ~2.2 Mpc along this direction. Apart from the southwestern infalling subcluster, the surface brightness profiles show multiple edges around radii of 30-40 arcmin. The azimuthally averaged temperature profile, as well as the deprojected density and pressure profiles, all show a sharp drop consistent with an outwardly-propagating shock front located at 40 arcmin, corresponding to the outermost edge of the giant radio halo observed at 352 MHz with the Westerbork Synthesis Radio Telescope. The shock front may be powering this radio emission. A clear entropy excess inside of r sub(500) reflects the violent merging events linked with these morphological features. Beyond r sub(500), the entropy profiles of the Coma Cluster along the relatively relaxed directions are consistent with the power-law behavior expected from simple models of gravitational large-scale structure formation. The pressure is also in agreement at these radii with the expected values measured from Sunyaev-Zel'dovich data from the Planck satellite. However, due to the large uncertainties associated with the Coma Cluster measurements, we cannot yet exclude an entropy flattening in this system consistent with that seen in more relaxed cool core clusters.
ABSTRACT A recent Chandra observation of the nearby galaxy cluster Abell 585 has led to the discovery of an extended X-ray jet associated with the high-redshift background quasar B3 0727+409, a ...luminous radio source at redshift z = 2.5. This is one of only few examples of high-redshift X-ray jets known to date. It has a clear extension of about 12″, corresponding to a projected length of ∼100 kpc, with a possible hot spot located 35″ from the quasar. The archival high resolution Very Large Array maps surprisingly reveal no extended jet emission, except for one knot about 1 4 from the quasar. The high X-ray to radio luminosity ratio for this source appears consistent with the amplification expected from the inverse Compton radiative model. This serendipitous discovery may signal the existence of an entire population of similar systems with bright X-ray and faint radio jets at high redshift, a selection bias that must be accounted for when drawing any conclusions about the redshift evolution of jet properties and indeed about the cosmological evolution of supermassive black holes and active galactic nuclei in general.
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