We present results of Hubble Space Telescope and Chandra X-Ray Observatory observations of globular clusters (GCs) and low-mass X-ray binaries (LMXBs) in the central regions of Centaurus A. Out of ...440 GC candidates, we find 41 host X-ray point sources that are most likely LMXBs. We fit King models to our GC candidates in order to measure their structural parameters. We find that GCs that host LMXBs are denser and more compact and have higher encounter rates and concentrations than the GC population as a whole. We show that the higher concentrations and masses are a consequence of the dependence of LMXB incidence on central density and size plus the general trend for denser GCs to have higher masses and concentrations. We conclude that neither concentration nor mass is a fundamental variable in determining the presence of LMXBs in GCs and that the more fundamental parameters relate to central density and size.
Clusters of galaxies have been extensively used to determine cosmological parameters. A major difficulty in making the best use of Sunyaev-Zel'dovich (SZ) and X-ray observations of clusters for ...cosmology is that using X-ray observations it is difficult to measure the temperature distribution and therefore determine the density distribution in individual clusters of galaxies out to the virial radius. Observations with the new generation of SZ instruments are a promising alternative approach. We use clusters of galaxies drawn from high-resolution adaptive mesh refinement cosmological simulations to study how well we should be able to constrain the large-scale distribution of the intracluster gas (ICG) in individual massive relaxed clusters using AMiBA in its configuration with 13 1.2 m diameter dishes (AMiBA13) along with X-ray observations. We show that non-isothermal Delta *b models provide a good description of the ICG in our simulated relaxed clusters. We use simulated X-ray observations to estimate the quality of constraints on the distribution of gas density, and simulated SZ visibilities (AMiBA13 observations) for constraints on the large-scale temperature distribution of the ICG. We find that AMiBA13 visibilities should constrain the scale radius of the temperature distribution to about 50% accuracy. We conclude that the upgraded AMiBA, AMiBA13, should be a powerful instrument to constrain the large-scale distribution of the ICG.
We present 30-GHz Sunyaev–Zel'dovich (SZ) observations of a sample of four galaxy clusters with a prototype of the One Centimetre Receiver Array (OCRA-p) which is mounted on the Torun 32-m telescope. ...The clusters (Cl 0016+16, MS 0451.6–0305, MS 1054.4–0321 and Abell 2218) are popular SZ targets and serve as commissioning observations. All four are detected with clear significance (4 –6σ) and values for the central temperature decrement are in good agreement with measurements reported in the literature. We believe that systematic effects are successfully suppressed by our observing strategy. The relatively short integration times required to obtain these results demonstrate the power of OCRA-p and its successors for future SZ studies.
We present observations, analysis, and results for the first-year operation of Array for Microwave Background Anisotropy (AMiBA), an interferometric experiment designed to study cosmology via the ...measurement of cosmic microwave background (CMB). AMiBA is the first CMB interferometer operating at 3 mm to have reported successful results, currently with seven close-packed antennas of 60 cm diameter giving a synthesized resolution of around 6'. During 2007, AMiBA detected the Sunyaev-Zel'dovich effects (SZEs) of six galaxy clusters at redshift 0.091 < = z < = 0.322. An observing strategy with on-off-source switching is used to minimize the effects from electronic offset and ground pickup. Planets were used to test the observational capability of AMiBA and to calibrate the conversion from correlator time-lag data to visibilities. The detailed formalism for data analysis is given. We summarize our early tests including observations of planets and quasars, and present images, visibility profiles, the estimated central coordinates, sizes, and SZE amplitudes of the galaxy clusters. Scientific implications are summarized. We also discuss possible systematic effects in the results.
Bright clusters of galaxies can be seen out to cosmological distances, and thus they can be used to derive cosmological parameters. Although the continuum X-ray emission from the intracluster gas is ...optically thin, the optical depth of resonant lines of ions of heavy elements can be larger than unity. In this Letter, we study the feasibility of deriving distances to clusters of galaxies by determining the spatial distribution of the intracluster gas from X-ray imaging and the optical depth from resonant emission lines (the XREL method). We solve the radiative transfer problem for line scattering in the hot intracluster gas using Monte Carlo simulations. We discuss the spatial and spectral resolutions needed to use the XREL method for accurate determination of distances, and hence cosmological parameters, and show that accurate distances will be obtained by applying this technique with the next generation of high-resolution X-ray spectrometers.
We investigate the scaling relations between the X-ray and the thermal Sunyaev-Zel'dovich effect properties of clusters of galaxies, using data taken during 2007 by the Y. T. Lee Array for Microwave ...Background Anisotropy (AMiBA) at 94 GHz for the six clusters A1689, A1995, A2142, A2163, A2261, and A2390. The scaling relations relate the integrated Compton-y parameter Y {sub 2500} to the X-ray-derived gas temperature T {sub e}, total mass M {sub 2500}, and bolometric luminosity L{sub X} within r {sub 2500}. Our results for the power-law index and normalization are both consistent with the self-similar model and other studies in the literature except for the Y {sub 2500}-L{sub X} relation, for which a physical explanation is given though further investigation may be still needed. Our results not only provide confidence for the AMiBA project but also support our understanding of galaxy clusters.
We demonstrate that constraints on cosmological parameters from the distribution of clusters as a function of redshift (dN/dz) are complementary to accurate angular diameter distance (D sub(A)) ...measurements to clusters, and their combination significantly tightens constraints on the energy density content of the universe. The number counts can be obtained from X-ray and/or Sunyaev-Zel'dovich (SZ) effect surveys, and the angular diameter distances can be determined from deep observations of the intracluster gas using its thermal bremsstrahlung X-ray emission and the SZ effect. We combine constraints from simulated cluster number counts expected from a 12 deg super(2) SZ cluster survey and constraints from simulated angular diameter distance measurements based on the X-ray/SZ method, assuming a statistical accuracy of 10% in the angular diameter distance determination of 100 clusters with redshifts less than 1.5. We find that Omega sub(m) can be determined within about 25%, Omega sub(lambda) within 20%, and w within 16%. We show that combined dN/dz + D sub(A) constraints can be used to constrain the different energy densities in the universe even in the presence of a few percent redshift dependent systematic error in D sub(A). We also address the question of how best to select clusters of galaxies for accurate diameter distance determinations. We show that the joint dN/dz + D sub(A) constraints on cosmological parameters for a fixed target accuracy in the energy density parameters are optimized by selecting clusters with redshift upper cutoffs in the range 0.5 ~ z ~ 1.
Double lobe radio sources associated with active galactic nuclei represent one of the longest studied groups in radio astronomy. A particular sub-group of double radio sources comprises the compact ...symmetric objects (CSOs). CSOs are distinguished by their prominent double structure and sub-kpc total size. It has been argued that the vast majority of high-luminosity CSOs (CSO 2s) represent a distinct class of active galactic nuclei with its own morphological structure and life-cycle. In this work, we present theoretical considerations regarding CSO 2s. We develop a semi-analytic evolutionary model, inspired by the results of large-scale numerical simulations of relativistic jets, that reproduces the features of the radio source population. We show that CSO 2s may be generated by finite energy injections and propose stellar tidal disruption events as a possible cause. We find that tidal disruption events of giant branch stars with masses \(\gtrsim1\) M\(_\odot\) can fuel these sources and discuss possible approaches to confirming this hypothesis. We predict that if the tidal disruption scenario holds, CSO 2s with sizes less than 400 pc should outnumber larger sources by more than a factor of \(10\). Our results motivate future numerical studies to determine whether the scenarios we consider for fueling and source evolution can explain the observed radio morphologies. Multiwavelength observational campaigns directed at these sources will also provide critical insight into the origins of these objects, their environments, and their lifespans.
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