Mass and Gas Profiles in A1689: Joint X-ray and Lensing Analysis

We carry out a comprehensive joint analysis of high quality HST/ACS and Chandra measurements of A1689, from which we derive mass, temperature, X-ray emission and abundance profiles. The X-ray emission is smooth and symmetric, and the lensing mass is centrally concentrated indicating a relaxed cluster. Assuming hydrostatic equilibrium we deduce a 3D mass profile that agrees simultaneously with both the lensing and X-ray measurements. However, the projected temperature profile predicted with this 3D mass profile exceeds the observed temperature by ~30% at all radii, a level of discrepancy comparable to the level found for other relaxed clusters. This result may support recent suggestions from hydrodynamical simulations that denser, more X-ray luminous small-scale structure can bias observed temperature measurements downward at about the same (~30%) level. We determine the gas entropy at 0.1r_{vir} (where r_{vir} is the virial radius) to be ~800 keV cm^2, as expected for a high temperature cluster, but its profile at >0.1r_{vir} has a power-law form with index ~0.8, considerably shallower than the ~1.1 index advocated by theoretical studies and simulations. Moreover, if a constant entropy ''floor'' exists at all, then it is within a small region in the inner core, r<0.02r_{vir}, in accord with previous theoretical studies of massive clusters.Comment: 18 pages, 20 figures, 7 tables, accepted for publication in MNRAS, minor changes to match published versio

Reconstructing the triaxiality of the galaxy cluster Abell 1689: solving the X-ray and strong lensing mass discrepancy

We present the first determination of the intrinsic triaxial shapes and tree-dimensional physical parameters of both dark matter (DM) and intra-cluster medium (ICM) for the galaxy cluster Abell 1689. We exploit the novel method we recently introduced (Morandi et al. 2010) in order to infer the tree-dimensional physical properties in triaxial galaxy clusters by combining jointly X-ray and strong lensing data. We find that Abell 1689 can be modeled as a triaxial galaxy cluster with DM halo axial ratios 1.24 +/- 0.13 and 2.37 +/- 0.11 on the plane of the sky and along the line of sight, respectively. We show that accounting for the three-dimensional geometry allows to solve the discrepancy between the mass determined from X-ray and strong gravitational lensing observations. We also determined the inner slope of the DM density profile alpha: we measure alpha = 0.90 +/- 0.05 by accounting explicitly for the 3D structure for this cluster, a value which is close to the cold dark matter (CDM) predictions, while the standard spherical modeling leads to the biased value alpha = 1.16 +/- 0.04. Our findings dispel the potential inconsistencies arisen in the literature between the predictions of the CDM scenario and the observations, providing further evidences that support the CDM scenario.Comment: Accepted for publication in Ap

The Contribution of Halos with Different Mass Ratios to the Overall Growth of Cluster-sized Halos

We provide a new observational test for a key prediction of the ΛCDM cosmological model: the contributions of mergers with different halo-to-main-cluster mass ratios to cluster-sized halo growth. We perform this test by dynamically analyzing 7 galaxy clusters, spanning the redshift range 0.13 < z_c < 0.45 and caustic mass range 0.4-1.5 10^(15)h_(0.73)^(-1) M_☉, with an average of 293 spectroscopically confirmed bound galaxies to each cluster. The large radial coverage (a few virial radii), which covers the whole infall region, with a high number of spectroscopically identified galaxies enables this new study. For each cluster, we identify bound galaxies. Out of these galaxies, we identify infalling and accreted halos and estimate their masses and their dynamical states. Using the estimated masses, we derive the contribution of different mass ratios to cluster-sized halo growth. For mass ratios between ~0.2 and ~0.7, we find a ~1σ agreement with ΛCDM expectations based on the Millennium simulations I and II. At low mass ratios, ≾ 0.2, our derived contribution is underestimated since the detection efficiency decreases at low masses, ~2 × 10^(14) h_(0.73)^(-1) M_☉. At large mass ratios, ≳ 0.7, we do not detect halos probably because our sample, which was chosen to be quite X-ray relaxed, is biased against large mass ratios. Therefore, at large mass ratios, the derived contribution is also underestimated

An expanded merger-tree description of cluster evolution

We model the formation and evolution of galaxy clusters in the framework of an extended dark matter halo merger-tree algorithm that includes baryons and incorporates basic physical considerations. Our modified treatment is employed to calculate the probability density functions of the halo concentration parameter, intracluster gas temperature, and the integrated Comptonization parameter for different cluster masses and observation redshifts. Scaling relations between cluster mass and these observables are deduced that are somewhat different than previous results. Modeling uncertainties in the predicted probability density functions are estimated. Our treatment and the insight gained from the results presented in this paper can simplify the comparison of theoretical predictions with results from ongoing and future cluster surveys.Comment: 11 pages, 9 figures, submitted to MNRA

Three-dimensional Multi-probe Analysis of the Galaxy Cluster A1689

We perform a 3D multi-probe analysis of the rich galaxy cluster A1689 by combining improved weak-lensing data from new BVRi'z' Subaru/Suprime-Cam observations with strong-lensing, X-ray, and Sunyaev-Zel'dovich effect (SZE) data sets. We reconstruct the projected matter distribution from a joint weak-lensing analysis of 2D shear and azimuthally integrated magnification constraints, the combination of which allows us to break the mass-sheet degeneracy. The resulting mass distribution reveals elongation with axis ratio ~0.7 in projection. When assuming a spherical halo, our full weak-lensing analysis yields a projected concentration of $c_{200c}^{2D}=8.9\pm 1.1$ ($c_{vir}^{2D}\sim 11$), consistent with and improved from earlier weak-lensing work. We find excellent consistency between weak and strong lensing in the region of overlap. In a parametric triaxial framework, we constrain the intrinsic structure and geometry of the matter and gas distributions, by combining weak/strong lensing and X-ray/SZE data with minimal geometric assumptions. We show that the data favor a triaxial geometry with minor-major axis ratio 0.39+/-0.15 and major axis closely aligned with the line of sight (22+/-10 deg). We obtain $M_{200c}=(1.2\pm 0.2)\times 10^{15} M_{\odot}/h$ and $c_{200c}=8.4\pm 1.3$, which overlaps with the $>1\sigma$ tail of the predicted distribution. The shape of the gas is rounder than the underlying matter but quite elongated with minor-major axis ratio 0.60+/-0.14. The gas mass fraction within 0.9Mpc is 10^{+3}_{-2}%. The thermal gas pressure contributes to ~60% of the equilibrium pressure, indicating a significant level of non-thermal pressure support. When compared to Planck's hydrostatic mass estimate, our lensing measurements yield a spherical mass ratio of $M_{Planck}/M_{GL}=0.70\pm 0.15$ and $0.58\pm 0.10$ with and without corrections for lensing projection effects, respectively.Comment: Accepted by ApJ. Minor textual changes to improve clarity (e.g., 5. HST STRONG-LENSING ANALYSIS). 26 pages, 17 figures. A version with high-resolution figures is available at http://www.asiaa.sinica.edu.tw/~keiichi/upfiles/Umetsu15/umetsu15.pd

Dynamical Study of A1689 from Wide-Field VLT/VIMOS Spectroscopy: Mass Profile, Concentration Parameter, and Velocity Anisotropy

We examine the dynamics structure of the rich cluster A1689, combining VLT/VIMOS spectroscopy with Subaru/Suprime-Cam imaging. The radial velocity distribution of $\sim 500$ cluster members is bounded by a pair of clearly defined velocity caustics, with a maximum amplitude of $\sim|4000|$ km/s at $\simeq$ 300 h$^{-1}$ kpc, beyond which the amplitude steadily declines, approaching zero velocity at a limiting radius of $\sim$ 2 h$^{-1}$ Mpc. We derive the 3D velocity anisotropy and galaxy number density profiles using a model-independent method to solve the Jeans equation, simultaneously incorporating the observed velocity dispersion profile, the galaxy counts from deep Subaru imaging, and our previously derived cluster mass profile from a joint lensing and X-ray analysis. The velocity anisotropy is found to be predominantly radial at large radius, becoming increasingly tangential towards the center, in accord with expectations. We also analyze the galaxy data independently of our previous analysis using two different methods: The first is based on a solution of the Jeans equation assuming an NFW form for the mass distribution, whereas in the second method the caustic amplitude is used to determine the escape velocity. The cluster virial mass derived by both of these dynamical methods is in good agreement with results from our earlier lensing and X-ray analysis. We also confirm the high NFW concentration parameter, with results from both methods combined to yield $c_{\rm vir}>13$ (1$\sigma$). The inferred virial radius is consistent with the limiting radius where the caustics approach zero velocity and where the counts of cluster members drop off, suggesting that infall onto A1689 is currently not significant.Comment: 12 pages, 10 figures, accepted for publication in Ap

The probability distribution of cluster formation times and implied Einstein Radii

We provide a quantitative assessment of the probability distribution function of the concentration parameter of galaxy clusters. We do so by using the probability distribution function of halo formation times, calculated by means of the excursion set formalism, and a formation redshift-concentration scaling derived from results of N-body simulations. Our results suggest that the observed high concentrations of several clusters are quite unlikely in the standard Lambda CDM cosmological model, but that due to various inherent uncertainties, the statistical range of the predicted distribution may be significantly wider than commonly acknowledged. In addition, the probability distribution function of the Einstein radius of A1689 is evaluated, confirming that the observed value of ~45" +/- 5" is very improbable in the currently favoured cosmological model. If, however, a variance of ~20% in the theoretically predicted value of the virial radius is assumed, than the discrepancy is much weaker. The measurement of similarly large Einstein radii in several other clusters would pose a difficulty to the standard model. If so, earlier formation of the large scale structure would be required, in accord with predictions of some quintessence models. We have indeed verified that in a viable early dark energy model large Einstein radii are predicted in as many as a few tens of high-mass clusters.Comment: 9 pages, 6 figures, submitted to MNRA

XMM-Newton Spectroscopy of the Starburst Dominated Ultra Luminous Infrared Galaxy NGC 6240

We present new XMM-Newton observation of the Ultra Luminous Infrared Galaxy (ULIRG) NGC 6240. We analyze the reflecting grating spectrometer (RGS) data, and data from the other instruments, and find a starburst dominated 0.5-3 keV spectrum with global properties resembling those observed in M82 but with a much higher luminosity. We show that the starburst region can be divided into an outer zone, beyond a radius of about 2.1 kpc, with a gas temperature of about 10^7 K and a central region with temperatures in the range (2-6) x 10^7 K. The gas in the outer region emits most of the observed Oviii Lyman-alpha line and the gas in the inner region the emission lines of higher ionization ions, including a strong Fexxv line. We also identify a small inner part, very close to the active nuclei, with typical Seyfert 2 properties including a large amount of photoionized gas producing a strong Fe K-alpha 6.4 keV line. The combined abundance, temperature and emission measure analysis indicates super solar Ne/O, Mg/O, Si/O, S/O and possibly also Fe/O. The analysis suggests densities in the range of (0.07-0.28) x epsilon^(-1/2) cm^(-3) and a total thermal gas mass of about 4 x 10^8 x epsilon^(1/2) solar masses, where epsilon is the volume filling factor. We used a simple model to argue that a massive starburst with an age of about 2 x 10^7 years can explain most of the observed properties of the source. NGC 6240 is perhaps the clearest case of an X-ray bright luminous AGN, in a merger, whose soft X-ray spectrum is dominated by a powerful starburst.Comment: 10 pages, 6 diagrams, accepted by ApJ, added a few minor change

Mapping the Universe: The 2010 Russell Lecture

Redshift surveys are a powerful tool of modern cosmology. We discuss two aspects of their power to map the distribution of mass and light in the universe: (1) measuring the mass distribution extending into the infall regions of rich clusters and (2) applying deep redshift surveys to the selection of clusters of galaxies and to the identification of very large structures (Great Walls). We preview the HectoMAP project, a redshift survey with median redshift z = 0.34 covering 50 square degrees to r= 21. We emphasize the importance and power of spectroscopy for exploring and understanding the nature and evolution of structure in the universe.Comment: 19 pages, 5 figures (2 videos available in the on-line journal article