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Register a new userAn X-ray and Optical Study of Matter Distribution in the Galaxy Cluster A 2319
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A new analysis of velocity distribution, optical photometry and X-ray surface brightness from ROSAT PSPC data of the galaxy cluster A 2319 is presented. The temperature profile derived from ASCA data (Markevitch et al.,1996) is taken into account. A method to check the hydrostatic model in the presence of a temperature gradient is proposed. Consistency of the hydrostatic isothermal model and the explanation of the beta-discrepancy are discussed. Galaxy and gas density profiles of the main component A 2319A are derived, allowing for the effect of the secondary component A 2319B. The inadequacy of a polytropic model, which would produce a binding mass decrease with respect to the isothermal beta-model, is discussed. A simple interpolation of the temperature profile provides instead an increase of the binding mass and a lower baryon fraction thus mitigating the baryon catastrophe. Assuming as typical the value f_b ~ 0.2, a comparison with the most recent estimate of Omega_b(nucl) implies for the cosmological parameter Omega_o less than 0.4.
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We report the first detailed X-ray and optical observations of the medium-distant cluster A33 obtained with the Beppo-SAX satellite and with the UH 2.2m and Keck II telescopes at Mauna Kea. The information deduced from X-ray and optical imaging and spectroscopic data allowed us to identify the X-ray source 1SAXJ0027.2-1930 as the X-ray counterpart of the A33 cluster. The faint, $F_{2-10 keV} approx 2.4 times 10^{-13} ergscm2$, X-ray source 1SAXJ0027.2-1930, $sim 2$ arcmin away from the optical position of the cluster as given in the Abell catalogue, is identified with the central region of A33. Based on six cluster galaxy redshifts, we determine the redshift of A33, $z=0.2409$; this is lower than the value derived by Leir and Van Den Bergh (1977). The source X-ray luminosity, $L_{2-10 keV} = 7.7 times 10^{43} ergs$, and intracluster gas temperature, $T = 2.9$ keV, make this cluster interesting for cosmological studies of the cluster $L_X-T$ relation at intermediate redshifts. Two other X-ray sources in the A33 field are identified. An AGN at z$=$0.2274, and an M-type star, whose emission are blended to form an extended X-ray emission $sim 4$ arcmin north of the A33 cluster. A third possibly point-like X-ray source detected $sim 3$ arcmin north-west of A33 lies close to a spiral galaxy at z$=$0.2863 and to an elliptical galaxy at the same redshift as the cluster.
We present joint X-ray and optical observations of the high redshift (z~0.83) lensing cluster CLJ0152.7-1357 made with the Chandra X-ray Observatory and the Keck telescope. We confirm the existence of significant substructure at both X-ray and optical wavelengths in the form of two distinct clumps, whose temperatures are 6.6(-1.5,+2.4) keV and 5.7(-1.6,+2.9) keV, respectively. The X-ray surface brightness profiles of the two clumps can be fitted by either a single beta-model or an NFW-like profile; the latter giving better fits to the central regions. We find that the X-ray derived mass of this cluster is in good agreement with independent lensing measurements. While its appearance indicates that the cluster has not reached a dynamical equilibrium state, its X-ray luminosity L_x, temperature T and dynamical mass M are consistent with the well-defined L_x-T and M-T relations for low-redshift galaxy clusters, which suggests that the dynamical properties of the clusters have remained almost unchanged since z~0.8.
Results are discussed of an X-ray and optical observation campaign of the low-mass X-ray binary A1246-58 performed with instruments on Satellite per Astronomia X (BeppoSAX), the Rossi X-ray Timing Explorer (RXTE), the X-ray Multi-mirror Mission (XMM-Newton), the Swift mission, and the Very Large Telescope. Spectra and flux time histories are studied. The most important results are the lack of hydrogen spectral features in the optical spectrum, supporting the proposition that this is an ultracompact X-ray binary (UCXB), the determination of a 4.3 kpc distance from time-resolved spectroscopy of thermonuclear X-ray bursts, and the detection of intermediately long thermonuclear bursts as seen in a number of other UCXBs. There is evidence for a Ne/O abundance ratio in the line of sight that is higher than solar and variable. This may be due to different changes in the ionization degrees of Ne and O, which may be related to the variable irradiating flux. We discuss the spectral variability and the peculiarities of the long-term light curve.
We present the results of Suzaku observation of the radio halo cluster Abell 2319. The metal abundance in the central cool region is found to be higher than the surrounding region, which was not resolved in the former studies. We confirm that the line-of-sight velocities of the intracluster medium in the observed region are consistent with those of the member galaxies of entire A2319 and A2319A subgroup for the first time, though any velocity difference within the region is not detected. On the other hand, we do not find any signs of gas motion relevant to A2319B subgroup. Hard X-ray emission from the cluster is clearly detected, but its spectrum is likely thermal. Assuming a simple single temperature model for the thermal component, we find that the upper limit of the non-thermal inverse Compton component becomes $2.6 times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ in the 10-40 keV band, which means that the lower limit of the magnetic field is 0.19 $mu$G with the radio spectral index 0.92. Although the results slightly depend on the detailed spectral modeling, it is robust that the upper limit of the power-law component flux and lower limit of the magnetic field strength become $sim 3 times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ and $sim 0.2 mu$G, respectively. Considering the lack of a significant amount of very hot ($sim 20$ keV) gas and the strong bulk flow motion, it is more likely that the relativistic non-thermal electrons responsible for the radio halo are accelerated through the intracluster turbulence rather than the shocks.
Determining the structure of galaxy clusters is essential for an understanding of large scale structure in the universe, and may hold important clues to the identity and nature of dark matter particles. Moreover, the core dark matter distribution may offer insight into the structure formation process. Unfortunately, cluster cores also tend to be the site of complicated astrophysics. X-ray imaging spectroscopy of relaxed clusters, a standard technique for mapping their dark matter distributions, is often complicated by the presence of their putative ``cooling flow gas, and the dark matter profile one derives for a cluster is sensitive to assumptions made about the distribution of this gas. Here we present a statistical analysis of these assumptions and their effect on our understanding of dark matter in galaxy clusters.
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