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Register a new userThe origin of X-ray emission of two distant (z>1) cluster candidate with XMM-Newton
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D.M. Neumann
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We present here a study of XMM-Newton data of two distant galaxy cluster candidates. One of these was discovered serendipitously in near infrared data, CL J0533-2411, the other one corresponds to the cluster EIS J0533-2412 part of the EIS cluster survey. The estimated redshift of CL J0533-2411 is z=1.2-1.7. EIS J0533-2412 is a rich system (Lambda_cl=299), with a spectroscopically confirmed redshift of z=1.3. Both galaxy concentrations show firm X-ray detections, located within 30 of their optical center. However, we cannot resolve the sources with XMM-Newton. If the X-ray emission originates from the X-ray emitting intra-cluster medium (ICM) it would be extremely concentrated which is rather unlikely (core radii below 14 h_{65}^{-1}kpc and 40 h_{65}^{-1}kpc, respectively). We argue that the X-ray sources are more likely AGN members of the galaxy concentrations. We set an upper limit for the bolometric luminosity of a hot ICM in the range ~0.7-2.1 10^{44} h_{65}^{-2}erg/s for CL J0533-2411, depending on the exact redshift. For EIS J0533-2412 the limit is L_bol=(6.2+/-1.4) 10^{43} h_{65}^{-2}erg/s. We interpret our result in the following way: EIS J0533-2412 (and possibly CL J0533-2411) are proto-clusters and show matter overdensities before collapse, which explains the low significance of extended X-ray emission.
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We report on the XMM-Newton (XMM) observation of RXJ1053.7+5735, one of the most distant (z = 1.26) X-ray selected clusters of galaxies, which also shows an unusual double-lobed X-ray morphology, indicative of possible cluster-cluster interaction. The cluster was discovered during our ROSAT deep pointings in the direction of the Lockman Hole. The XMM observations were performed with the European Photon Imaging Camera (EPIC) during the performance verification phase. Total effective exposure time was ~ 100 ksec. The best fit temperature based on a simultaneous fit of spectra from the all EPIC cameras is 4.9(+1.5/-0.9) keV. Metallicity is poorly constrained even using the joint fit of all spectra, with an upper limit on the iron abundance of 0.62 solar. Using the best fit model parameters, we derived a bolometric luminosity of L(bol) = 3.4x10^44 h_{50}^-2 erg /s. Despite the fact that it was observed at fairly large off-axis angle, the temperature errors are much smaller compared with those of typical measurements based on ASCA or Beppo-Sax observations of z > 0.6 clusters, demonstrating the power of the XMM for determining the X-ray temperature for high-z clusters. The measured temperature and luminosity show that one can easily reach the intrinsically X-ray faint and cool cluster regime comparable with those of z ~ 0.4 clusters observed by past satellites. The new cluster temperature and L(bol) we have measured for RXJ1053.7+5735 is consistent with a weak/no evolution of the L(bol) - Tx relation out to z ~ 1.3, which lends support to a low Omega universe, although more data-points of z > 1 clusters are required for a more definitive statement. The caution has to be also exercised in interpreting the result, because of the uncertainty associated with the dynamical status of this cluster.
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We aim at clarifying the nature of the emission of two spatially related unidentified X-ray sources detected with XMM-Newton telescope at intermediate-low Galactic latitude. Observations reveal a point-like source aligned with elongated diffuse emission. The X-ray spectra are best-fitted by absorbed power laws with photon indices ~1.7 for the point-like and ~2.0 for the extended one. Both sources show nonthermal radio-continuum counterparts that might indicate a physical association. From the available data, we did not detect variability on the point-like source in several timescales. Two possible scenarios are analyzed: first, based on HI line absorption, assuming a Galactic origin, we infer a distance upper bound of <2 kpc, which poses a constraint on the height over the Galactic plane of <200 pc and on the linear size of the system of <2.3 pc. In this case, the X-ray luminosities are >10^32 erg/s and >7.5 x 10^32 erg/s, for the point-like and extended sources, respectively; second, an extra-Galactic nature is discussed, where the point-like source might be the core of a radio galaxy and the extended source its lobe. In this case, we compare derived fluxes, spectral indices, and spatial correlation with those typical from the radio galaxy population, showing the feasibility of this alternative astrophysical scenario. From the available observational evidence, we suggest that the most promising scenario to explain the nature of these sources is a system consisting of a one-sided radio galaxy, where the point-like source is an active galactic nucleus and the extended source corresponds to the emission from its lobe. Other possibilities include a PSR/PWN origin, where the radio/X-ray emission originates from the synchrotron cooling of relativistic particles in the PSR magnetic field or a casual alignment between two unrelated sources, such as an AGN core and a Galactic X-ray blob.
We present the largest sample of spectroscopically confirmed X-ray luminous high-redshift galaxy clusters to date comprising 22 systems in the range 0.9<z<sim1.6 as part of the XMM-Newton Distant Cluster Project (XDCP). All systems were initially selected as extended X-ray sources over 76.1 deg^2 of non-contiguous deep archival XMM-Newton coverage. We test and calibrate the most promising two-band redshift estimation techniques based on the R-z and z-H colors for efficient distant cluster identifications and find a good redshift accuracy performance of the z-H color out to at least zsim1.5, while the redshift evolution of the R-z color leads to increasingly large uncertainties at z>sim0.9. We present first details of two newly identified clusters, XDCP J0338.5+0029 at z=0.916 and XDCP J0027.2+1714 at z=0.959, and investigate the Xray properties of SpARCS J003550-431224 at z=1.335, which shows evidence for ongoing major merger activity along the line-of-sight. We provide X-ray properties and luminosity-based total mass estimates for the full sample, which has a median system mass of M200simeq2times10^14Modot. In contrast to local clusters, the z>0.9 systems do mostly not harbor central dominant galaxies coincident with the X-ray centroid position, but rather exhibit significant BCG offsets from the X-ray center with a median value of about 50 kpc in projection and a smaller median luminosity gap to the second-ranked galaxy of sim0.3mag. We estimate a fraction of cluster-associated NVSS 1.4GHz radio sources of about 30%, preferentially located within 1 from the X-ray center. The galaxy populations in z>sim1.5 cluster environments show first evidence for drastic changes on the high-mass end of galaxies and signs for a gradual disappearance of a well-defined cluster red-sequence as strong star formation activity is observed in an increasing fraction of massive galaxies down to the densest core regions.
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.
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