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Register a new userXMM observation of the dynamically young galaxy cluster CL 0939+4713
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Elisabetta De Filippis
Publication date
2003
fields
Physics
and research's language is
English
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We present an XMM observation of the distant galaxy cluster CL 0939+4713. The X-ray image shows pronounced substructure, with two main subclusters forming the cluster core. This is an indication that the cluster is a dynamically young system. This conclusion is supported by the temperature distribution: a hot region is found between the two main subclusters indicating that they are at the beginning of a major merger, and that they will collide in a few hundreds of Myr. The intra-cluster gas of CL 0939+4713 shows inhomogeneities in the metal distribution, with the optically richer subcluster having a higher metallicity.
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RBS797 and CL 0939+4713 are two intermediate red-shift clusters ($z=0.35-0.41$). They have very different morphologies but both show surprisingly interesting structures. RBS797 looks relaxed, with an almost circular morphology; a CHANDRA observation of this cluster has revealed two deep depressions in the X-ray emission near the core. CL 0939+4713 has instead an irregular morphology with evident substructures which seem to be in the process of merging.
We present results from the XMM-Newton observation of the binary cluster A1750 at z = 0.086. We have performed a detailed study of the surface brightness, temperature and entropy distribution and confirm that the two main clusters of the system (A1750 N and A1750 C) have just started to interact. From the temperature distribution, we calculate that they are likely to merge sometime in the next 1 Gyr. The more massive cluster, A1750 C, displays a more complicated temperature structure than expected. We detect a hot region associated with a density jump ~450 kpc east of the cluster centre, which appears to be a shock wave. This shock is not connected with the binary merger, but it is intrinsic to A1750 C itself. From simple physical arguments and comparison with numerical simulations, we argue that this shock is related to a merging event that A1750 C has suffered in the past 1-2 Gyr. The larger scale structure around A1750 suggests that the system belongs to a rich supercluster, which would presumably increase the likelihood of merger events. These new XMM-Newton data thus show that A1750 is a complex system, where two clusters are starting to interact before having re-established equilibrium after a previous merger. This merger within a merger indicates that the present day morphology of clusters may depend not only on on-going interactions or the last major merging event, but also on the more ancient merger history, especially in dense environments.
An XMM-Newton imaging spectroscopy analysis of the galaxy cluster A1644 is presented. A1644 is a complex merging system consisting of a main and a sub cluster. A trail of cool, metal-rich gas has been discovered close to the sub cluster. The combination of results from X-ray, optical, and radio data, and a comparison to a hydrodynamical simulation suggest that the sub cluster has passed by the main cluster off-axis and a fraction of its gas has been stripped off during this process. Furthermore, for this merging system, simple effects are illustrated which can affect the use of clusters as cosmological probes. Specifically, double clusters may affect estimates of the cluster number density when treated as a single system. Mergers, as well as cool cores, can alter the X-ray luminosity and temperature measured for clusters, causing these values to differ from those expected in equilibrium.
We report on a 20 ksec XMM observation of the distant cluster RXJ1120.1+4318, discovered at z=0.6 in the SHARC survey. The cluster has a regular spherical morphology, suggesting it is in a relaxed state. The combined fit of the EPIC/MOS&pn camera gives a cluster mean temperature of kT=5.3pm0.5 keV with an iron abundance of 0.47pm0.19. The temperature profile, measured for the first time at such a redshift, is consistent with an isothermal atmosphere up to half the virial radius. The surface brightness profile, measured nearly up to the virial radius, is well fitted by a beta-model, with beta =0.78[+0.06,-0.04] and a core radius of thetac = 0.44[+0.06,-0.04] arcmin. We compared the properties of RXJ1120.1+4318 with the properties of nearby clusters for two cosmological models: an Einstein - de Sitter Universe and a flat low density Universe with Omega0=0.3. For both models, the scaled emission measure profile beyond the core, the gas mass fraction and luminosity are consistent with the expectations of the self-similar model of cluster formation, although a slightly better agreement is obtained for a low density Universe. There is no evidence of a central cooling flow, in spite of the apparent relaxed state of the cluster. This is consistent with its estimated cooling time, larger than the age of the Universe at the cluster redshift. The entropy profile shows a flat core with a central entropy of ~ 140 keV cm^2, remarkably similar to the entropy floor observed in nearby clusters, and a rising profile beyond typically 0.1 virial radius. Implications of our results, in terms of non-gravitational physics in cluster formation, are discussed.
We report XMM-Newton observations of the young open cluster NGC 2547 which allow us to characterise coronal activity in solar-type stars at an age of 30 Myr. X-ray emission peaks among G-stars at luminosities (0.3-3keV) of Lx~10^{30.5} erg/s and declines to Lx<=10^{29.0} erg/s among M-stars. Coronal spectra show evidence for multi-temperature differential emission measures and low coronal metal abundances (Z~0.3). The G- and K-type stars follow the same relationship between X-ray activity and Rossby number established in older clusters and field stars, although most solar-type stars in NGC 2547 exhibit saturated/super-saturated X-ray activity levels. Median levels of Lx and Lx/Lbol in the solar-type stars of NGC 2547 are similar to T-Tauri stars of the Orion Nebula cluster (ONC), but an order of magnitude higher than in the older Pleiades. The spread in X-ray activity levels among solar-type stars in NGC 2547 is much smaller than in older or younger clusters. Coronal temperatures increase with Lx, Lx/Lbol and surface X-ray flux. Active solar-type stars in NGC 2547 have coronal temperatures between those in the ONC and the most active older ZAMS stars. A flaring rate (for total flare energies [0.3-3keV] >10^{34} erg) of 1 every 350^{+350}_{-120} ks was found for solar-type stars, similar to rates found in the ONC and Pleiades. Comparison with ROSAT HRI data taken 7 years previously reveals that only 10-15 percent of solar-type stars or stars with Lx>3x10^{29} erg/s exhibit X-ray variability by more than a factor of two. The similar levels of X-ray activity and rate of occurrence for large flares in NGC 2547 and the ONC demonstrate that the X-ray radiation environment around young solar-type stars remains relatively constant over their first 30 Myr (abridged).
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