Abell 370: A Cluster with a Pronounced Triaxial Morphology

We here combine Sunyaev-Zel'dovich effect, X-ray observations and spectroscopic redshifts of member galaxies, to constrain the intrinsic three-dimensional shape of the galaxy cluster: Abell 370. The cluster turns out to be strongly elongated along the l.o.s., with two (or more) substructures in the process of merging. Spectroscopy further suggests that the process must be taking place at a small angle respect to the l.o.s.Comment: 7 pages, 2 figures. Contribution to the Proceedings of the COSPAR Scientific Assembly, E1.2 "Clusters of Galaxies: New Insights from XMM-Newton, Chandra and INTEGRAL", Paris (France), July 19-20, 2004. Accepted for publication in Advances in Space Researc

Measuring Gravitational Lensing Flexions in Abell 1689 Using an Analytic Image Model

Measuring dark matter substructure within galaxy cluster haloes is a fundamental probe of the Lambda-CDM model of structure formation. Gravitational lensing is a technique for measuring the total mass distribution which is independent of the nature of the gravitating matter, making it a vital tool for studying these dark-matter dominated objects. We present a new method for measuring weak gravitational lensing flexions, the gradients of the lensing shear field, to measure mass distributions on small angular scales. While previously published methods for measuring flexions focus on measuring derived properties of the lensed images, such as shapelet coefficients or surface brightness moments, our method instead fits a mass-sheet-transformation-invariant Analytic Image Model (AIM) to the each galaxy image. This simple parametric model traces the distortion of lensed image isophotes and constrains the flexion fields. We test the AIM method using simulated data images with realistic noise and a variety of unlensed image properties, and show that it successfully reproduces the input flexion fields. We also apply the AIM method for flexion measurement to Hubble Space Telescope observations of Abell 1689, and detect mass structure in the cluster using flexions measured with the AIM method.Comment: 44 pages, 4 figures, 3 tables. Accepted to ApJ. V2 (published version) has minor changes from V1; ApJ 736 (2011

Magnetic Fields, Relativistic Particles, and Shock Waves in Cluster Outskirts

It is only now, with low-frequency radio telescopes, long exposures with high-resolution X-ray satellites and gamma-ray telescopes, that we are beginning to learn about the physics in the periphery of galaxy clusters. In the coming years, Sunyaev-Zeldovich telescopes are going to deliver further great insights into the plasma physics of these special regions in the Universe. The last years have already shown tremendous progress with detections of shocks, estimates of magnetic field strengths and constraints on the particle acceleration efficiency. X-ray observations have revealed shock fronts in cluster outskirts which have allowed inferences about the microphysical structure of shocks fronts in such extreme environments. The best indications for magnetic fields and relativistic particles in cluster outskirts come from observations of so-called radio relics, which are megaparsec-sized regions of radio emission from the edges of galaxy clusters. As these are difficult to detect due to their low surface brightness, only few of these objects are known. But they have provided unprecedented evidence for the acceleration of relativistic particles at shock fronts and the existence of muG strength fields as far out as the virial radius of clusters. In this review we summarise the observational and theoretical state of our knowledge of magnetic fields, relativistic particles and shocks in cluster outskirts.Comment: 34 pages, to be published in Space Science Review

Measuring the three dimensional structure of galaxy clusters. Application to a sample of 25 clusters.

We discuss a method to constrain the intrinsic shapes of galaxy clusters by combining X-Ray and Sunyaev-Zeldovich observations. The method is applied to a sample of 25 X-Ray selected clusters, with measured Sunyaev-Zeldovich temperature decrements. The sample turns out to be slightly biased, with strongly elongated clusters preferentially aligned along the line of sight. This result demonstrates that X-Ray selected cluster samples may be affected by morphological and orientation effects even if a relatively high threshold signal-to-noise ratio is used to select the sample. A large majority of the clusters in our sample exhibit a marked triaxial structure; the spherical hypothesis is strongly rejected for most sample members. Cooling flow clusters do not show preferentially regular morphologies. We also show that identification of multiple gravitationally lensed images, together with measurements of the Sunyaev-Zeldovich effect and X-Ray surface brightness, can provide a simultaneous determination of the three dimensional structure of a cluster, of the Hubble constant, and the cosmological energy density parameters

ASCA and ROSAT observations of distant, massive cooling flows.

We present the results from a detailed ASCA/ROSAT X-ray study of three distant, massive cooling flows: Zwicky 3146 (z = 0.291), Abell 1835 (z = 0.252) and E 1455 + 223 (Zwicky 7160; z = 0.258). Using multiphase models fitted to the ASCA spectra, we determine values for the temperature, metallicity, luminosity and cooling rates in the clusters. These results are combined with deprojection analyses of the ROSAT images to provide detailed constraints on the mass distributions in the systems, and on the properties of their cooling flows. The spectral and imaging data identify these clusters as three of the most massive cooling flows known, with mass deposition rates of ∼1400, 2300 and 1500 M⊙ yr−1 respectively. We highlight the need for multiphase models to model consistently the spectral and imaging X-ray data, and discuss the importance of using these models in X-ray determinations of the cluster masses. We also present results from an extensive optical study of the clusters and discuss the implications of new results on gravitational lensing in Abell 1835, presented more fully in a forthcoming companion paper by Edge et al. The lensing data provide an independent constraint on the distribution of mass in the cluster, in good agreement with the results from the multiphase (though not singlephase) X-ray analysis. We present measurements of the galaxy distributions in Abell 1835 and E 1455 + 223, and relate these to the distributions of the total mass. The ASCA spectra place firm constraints on the column density of intrinsic X-ray-absorbing material in the clusters. Abell 1835 and E 1455 + 223 exhibit large intrinsic column densities [NH∼(3 – 4) × 1021 atom cm−2] associated with their cooling flows. These clusters also exhibit significant amounts of reddening in theoptical spectra of their central galaxies. The data for Zwicky 3146 indicate lower levels of X-ray absorption and reddening. All three clusters exhibit excellent alignment between the position angles of their X-ray emission and the optical emission from their dominant cluster galaxies

The State of the Warm and Cold Gas in the Extreme Starburst at the Core of the Phoenix Galaxy Cluster (SPT-CLJ2344-4243)

We present new optical integral field spectroscopy (Gemini South) and submillimeter spectroscopy (Submillimeter Array) of the central galaxy in the Phoenix cluster (SPT-CLJ2344-4243). This cluster was previously reported to have a massive starburst (~800 M ☉ yr–1) in the central, brightest cluster galaxy, most likely fueled by the rapidly cooling intracluster medium. These new data reveal a complex emission-line nebula, extending for >30 kpc from the central galaxy, detected at [O II]λλ3726, 3729, [O III]λλ4959, 5007, Hβ, Hγ, Hδ, [Ne III]λ3869, and He II λ4686. The total Hα luminosity, assuming Hα/Hβ = 2.85, is L Hα = 7.6 ± 0.4 ×1043 erg s–1, making this the most luminous emission-line nebula detected in the center of a cool core cluster. Overall, the relative fluxes of the low-ionization lines (e.g., [O II], Hβ) to the UV continuum are consistent with photoionization by young stars. In both the center of the galaxy and in a newly discovered highly ionized plume to the north of the galaxy, the ionization ratios are consistent with both shocks and active galactic nucleus (AGN) photoionization. We speculate that this extended plume may be a galactic wind, driven and partially photoionized by both the starburst and central AGN. Throughout the cluster we measure elevated high-ionization line ratios (e.g., He II/Hβ, [O III]/Hβ), coupled with an overall high-velocity width (FWHM gsim 500 km s–1), suggesting that shocks are likely important throughout the interstellar medium of the central galaxy. These shocks are most likely driven by a combination of stellar winds from massive young stars, core-collapse supernovae, and the central AGN. In addition to the warm, ionized gas, we detect a substantial amount of cold, molecular gas via the CO(3-2) transition, coincident in position with the galaxy center. We infer a molecular gas mass of $M_{{\rm H_2}}$ = 2.2 ± 0.6 × 1010 M ☉, which implies that the starburst will consume its fuel in ~30 Myr if it is not replenished. The L IR/$M_{{\rm H_2}}$ that we measure for this cluster is consistent with the starburst limit of 500 L ☉/M ☉, above which radiation pressure is able to disperse the cold reservoir. The combination of the high level of turbulence in the warm phase and the high L IR/$M_{{\rm H_2}}$ ratio suggests that this violent starburst may be in the process of quenching itself. We propose that phases of rapid star formation may be common in the cores of galaxy clusters, but so short-lived that their signatures are quickly erased and appear only in a subsample of the most strongly cooling clusters

The Chandra Deep Field North Survey. XIII. 2 Ms point-source catalogs

We present point-source catalogs for the 2 Ms exposure of the Chandra Deep Field North, currently the deepest X-ray observation of the universe in the 0.58.0 keV band. Five hundred and three (503) X-ray sources are detected over an 448 arcmin2 area in up to seven X-ray bands. Twenty (20) of these X-ray sources lie in the central 5.3 arcmin2 Hubble Deep Field North (13,600 sources deg-2). The on-axis sensitivity limits are 2.5 × 10-17 ergs cm-2 s-1 (0.52.0 keV) and 1.4 × 10-16 ergs cm-2 s-1 (28 keV). Source positions are determined using matched-filter and centroiding techniques; the median positional uncertainty is 03. The X-ray colors of the detected sources indicate a broad variety of source types, although absorbed AGNs (including a small number of possible Compton-thick sources) are clearly the dominant type. We also match lower significance X-ray sources to optical counterparts and provide a list of 79 optically bright (R 23) lower significance Chandra sources. The majority of these sources appear to be starburst and normal galaxies. The average backgrounds in the 0.52.0 keV and 28 keV bands are 0.056 and 0.135 counts Ms-1 pixel-1, respectively. The background count distributions are very similar to Poisson distributions. We show that this 2 Ms exposure is approximately photon limited in all seven X-ray bands for regions close to the aim point, and we predict that exposures up to 25 Ms (0.52.0 keV) and 4 Ms (28 keV) should remain nearly photon limited. We demonstrate that this observation does not suffer from source confusion within 6 of the aim point, and future observations are unlikely to be source-confusion limited within 3 of the aim point even for source densities exceeding 100,000 deg-2. These analyses directly show that Chandra can achieve significantly higher sensitivities in an efficient, nearly photon-limited manner and be largely free of source confusion. To allow consistent comparisons, we have also produced point-source catalogs for the 1 Ms Chandra Deep Field South (CDF-S). Three hundred and twenty-six (326) X-ray sources are included in the main Chandra catalog, and an additional 42 optically bright X-ray sources are included in a lower significance Chandra catalog. We find good agreement with the photometry of the previously published CDF-S catalogs; however, we provide significantly improved positional accuracy