ESA; CNES (France); CNRS/INSU-IN2P3-INP (France); ASI (Italy); CNR (Italy); INAF (Italy); NASA (USA); DoE (USA); STFC (UK); UKSA (UK); CSIC (Spain); MINECO (Spain); JA (Spain); RES (Spain); Tekes (Finland); AoF (Finland); CSC (Finland); DLR (Germany); MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO (Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); ERC (EU); PRACE (EU); Higher Education Funding Council for England; Science and Technology Facilities Council; Alfred P. Sloan Foundation; National Science Foundation; US Department of Energy Office of Science

Planck 2015 results

The ACS Virgo Cluster Survey consists of HST ACS imaging for 100 early-type galaxies in the Virgo Cluster, observed in the F475W (≈SDSS g) and F850LP (≈SDSS z) filters. We derive distances for 84 of these galaxies using the method of surface brightness fluctuations (SBFs), present the SBF distance catalog, and use this database to examine the three-dimensional distribution of early-type galaxies in the Virgo Cluster. The SBF distance moduli have a mean (random) measurement error of 0.07 mag (0.5 Mpc), or roughly 3 times better than previous SBF measurements for Virgo Cluster galaxies. Five galaxies lie at a distance of d ≈ 23 Mpc and are members of the W' cloud. The remaining 79 galaxies have a narrow distribution around our adopted distance of d = 16.5 ± 0.1 (random mean error) ±1.1 Mpc (systematic). The rms distance scatter of this sample is σ(d) = 0.6 ± 0.1 Mpc, with little or no dependence on morphological type or luminosity class (i.e., 0.7 ± 0.1 and 0.5 ± 0.1 Mpc for the giants and dwarfs, respectively). The back-to-front depth of the cluster measured from our sample of early-type galaxies is 2.4 ± 0.4 Mpc (i.e., ±2 σ of the intrinsic distance distribution). The M87 (cluster A) and M49 (cluster B) subclusters are found to lie at distances of 16.7 ± 0.2 and 16.4 ± 0.2 Mpc, respectively. There may be a third subcluster associated with M86. A weak correlation between velocity and line-of-sight distance may be a faint echo of the cluster velocity distribution not having yet completely virialized. In three dimensions, Virgo's early-type galaxies appear to define a slightly triaxial distribution, with axis ratios of (1 : 0.7 : 0.5). The principal axis of the best-fit ellipsoid is inclined ~20°-40° from the line of sight, while the galaxies belonging to the W' cloud lie on an axis inclined by ~10°-15°.

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The ACS Virgo Cluster Survey. XIII. SBF Distance Catalog and the Three-Dimensional Structure of the Virgo Cluster

We present the catalogue of the REFLEX Cluster Survey providing information on the X-ray properties, redshifts, and some identification details of the clusters in the REFLEX sample. The catalogue describes a statistically complete X-ray flux-limited sample of 447 galaxy clusters above an X-ray flux of 3 x 10 -12 erg s -1 cm -2 (0.1 to 2.4 keV) in an area of 4.24 ster in the southern sky. The cluster candidates were first selected by their X-ray emission in the ROSAT-A11 Sky Survey and subsequently spectroscopically identified in the frame of an ESO key programme. Previously described tests have shown that the sample is more than 90% complete and there is a conservative upper limit of 9% on the fraction of clusters with a dominant X-ray contamination from AGN. In addition to the cluster catalogue we also describe the complete selection criteria as a function of the sky position and the conversion functions used to analyse the X-ray data. These are essential for the precise statistical analysis of the large-scale cluster distribution. This data set is at present the largest, statistically complete X-ray galaxy cluster sample. Together with these data set we also provide for the first time the full three-dimensional selection function. The sample forms the basis of several cosmological studies, one of the most important applications being the assessment of the statistics of the large-scale structure of the universe and the test of cosmological models. Part of these cosmological results have already been published.

https://www.aanda.org/articles/aa/pdf/2004/37/aa0484-03.pdf

The ROSAT-ESO Flux Limited X-ray (REFLEX) Galaxy cluster survey. V. The cluster catalogue

We present the all-sky Planck catalogue of Sunyaev-Zeldovich (SZ) sources detected from the 29 month full-mission data. The catalogue (PSZ2) is the largest SZ-selected sample of galaxy clusters yet produced and the deepest all-sky catalogue of galaxy clusters. It contains 1653 detections, of which 1203 are confirmed clusters with identified counterparts in external data-sets, and is the first SZ-selected cluster survey containing > $10^3$ confirmed clusters. We present a detailed analysis of the survey selection function in terms of its completeness and statistical reliability, placing a lower limit of 83% on the purity. Using simulations, we find that the Y5R500 estimates are robust to pressure-profile variation and beam systematics, but accurate conversion to Y500 requires. the use of prior information on the cluster extent. We describe the multi-wavelength search for counterparts in ancillary data, which makes use of radio, microwave, infra-red, optical and X-ray data-sets, and which places emphasis on the robustness of the counterpart match. We discuss the physical properties of the new sample and identify a population of low-redshift X-ray under- luminous clusters revealed by SZ selection. These objects appear in optical and SZ surveys with consistent properties for their mass, but are almost absent from ROSAT X-ray selected samples.

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Planck 2015 results. XXVII. The Second Planck Catalogue of Sunyaev-Zeldovich Sources

Although dark matter is a central element of modern cosmology, the history of how it became accepted as part of the dominant paradigm is often ignored or condensed into an anecdotal account focused around the work of a few pioneering scientists. The aim of this review is to provide a broader historical perspective on the observational discoveries and the theoretical arguments that led the scientific community to adopt dark matter as an essential part of the standard cosmological model.

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History of dark matter

We present a compilation of redshifts for 1572 Abell, Corwin, & Olowin (ACO) clusters, referenced to both the heliocentric and cosmic background radiation reference frames, and 395 velocity dispersions corrected to the reference frame of the cluster, available from the literature as of 1998 December. We present an additional list of 81 ACO clusters with published redshifts which are probably those of galaxies or groups superimposed on, or near, the ACO cluster position.

https://iopscience.iop.org/article/10.1086/313274/pdf

A Compilation of Redshifts and Velocity Dispersions for ACO Clusters

Integrated H I profiles were detected for 34 of 51 Hickson compact groups (HCGs) of galaxies, and sensitive upper limits to the H I flux density were measured for the other 17. About 60 percent of the galaxies within compact groups are spirals, and a significant tendency exists for the fraction of elliptical galaxies to increase with group surface brightness. The amount of dark matter within the compact group region is negligibly small. An HCG on average contains half as much neutral hydrogen as a loose group with a similar spectrum of galaxy luminosities and morphological types, implying that compact groups are independent dynamical entities and not transient or projected configurations of loose groups. The observed fraction of galaxies which are luminous enough to be possible merger products of compact groups is small compared with the fraction required by the theory of dynamical friction. A clear discrepancy thus exists between solid empirical evidence and a straightforward prediction of Newtonian dynamical theory in a setting which does not permit a dark matter explanation. 44 references.

Herbert J. Rood

Papers

A Compilation of Redshifts and Velocity Dispersions for ACO Clusters

Neutral hydrogen in compact groups of galaxies

A Catalog of Morphological Properties of the 2712 Abell Clusters

Empirical Properties of the Mass Discrepancy in Groups and Clusters of Galaxies.

The Neighborhood of a Compact Group of Galaxies