Cosmography and Data Visualization Daniel Pomar`ede Institut de Recherche sur les Lois Fondamentales de l'Univers CEA, Universit´eParis-Saclay, 91191 Gif-sur-Yvette, France H´el`eneM. Courtois Universit´eClaude Bernard Lyon I/CNRS/IN2P3, Institut de Physique Nucl´eaire, Lyon, France Yehuda Hoffman Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel R. Brent Tully, Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA ABSTRACT Cosmography, the study and making of maps of the universe or cosmos, is a field where vi- sual representation benefits from modern three-dimensional visualization techniques and media. At the extragalactic distance scales, visualization is contributing in understanding the complex structure of the local universe, in terms of spatial distribution and flows of galaxies and dark mat- ter. In this paper, we report advances in the field of extragalactic cosmography obtained using the SDvision visualization software in the context of the Cosmicflows Project. Here, multiple vi- sualization techniques are applied to a variety of data products: catalogs of galaxy positions and galaxy peculiar velocities, reconstructed velocity field, density field, gravitational potential field, velocity shear tensor viewed in terms of its eigenvalues and eigenvectors, envelope surfaces en- closing basins of attraction. These visualizations, implemented as high-resolution images, videos, and interactive viewers, have contributed to a number of studies: the cosmography of the local part of the universe, the nature of the Great Attractor, the discovery of the boundaries of our home supercluster of galaxies Laniakea, the mapping of the cosmic web, the study of attractors and repellers. arXiv:1702.01941v1 [astro-ph.CO] 7 Feb 2017 1. Introduction has been sought by astronomers as an essential mean to promote understanding. Such objects as Throughout the ages, astronomers have strived the armillary spheres, dating back from the Hel- to materialize their discoveries and understanding lenistic world, or the modern era orreries used to of the cosmos by the means of visualizations. The mechanically model the solar system, played an oldest known depiction of celestial objects, the Ne- important role in the history of astronomy. To- bra sky disc, dates back from the Bronze age, 3600 day, computer-based interactive three-dimensional years ago (Benson 2014). While most of the astro- visualization techniques have become a fruitful re- nomical representations are projections to two di- search tool. Here, we present the impact of vi- mensional sketches and images, the introduction sualization on cosmography in the context of the of the third dimension in depictive apparatuses Cosmicflows Project. 1 The discipline of cosmography is both very old and 5). This early cartography was severely lim- and very young. Since ancient times, societies ited by the Zone of Avoidance associated with the have tried to understand their place in the cos- obscuration caused by the dust and stars of our mos and have created representations to express own galactic disk. This Zone of Avoidance creates their ideas. Today we have learned that we live a three-dimensional wedge inside which direct ob- in an expanding universe, 13.7 billion years old, servations are not possible. It is a strength of filled with mysterious dark matter and dark en- the Cosmicflows program that it provides a recon- ergy, with galaxies in lattices of the cosmic web. struction of the structures lying within the Zone of However our representations of the structure of Avoidance using the gravitational influence they the universe, cosmography, are remarkably primi- exert on galaxies lying nearby. Three-dimensional tive. We only have good knowledge of a tiny frac- density contour maps within 8000 km/s were pre- tion of the potentially visible universe. The quest sented by Hudson (1993), see Figure 10 therein; of the present research is to substantially improve these show from two complementary viewpoints our understanding of our local neighborhood of the how filaments and high-density blobs such as universe. Inevitably, what we know degrades with Virgo-Centaurus-Hydra, Perseus-Pisces, Pavo, distance. However, nearby our emerging picture is Coma are organized. Using the 2M++ galaxy rich in detail and, farther away, the outer bound- redshift compilation based on 2MRS, 6dFGRS- aries where our maps blur into the background DR3 and SDSS-DR7, Lavaux and Hudson (2011) confusion are being pushed back dramatically. presented maps of the density field within 15,000 The Cosmicflows Project aims at the recon- km/s. Using the Cosmicflows-1 Catalog, Courtois struction and mapping of structure of the Local et al (2012) presented maps of both density and Universe using peculiar velocities of galaxies as velocity fields within 3000 km/s with reconstruc- tracers of the source density field; it has released tion of the Local Void and the Great Attractor. three catalogs, Cosmicflows-1 with 1791 galax- ies (Tully et al. 2008), Cosmicflows-2 with 8161 2. The Cosmicflows program galaxies (Tully et al. 2013), Cosmicflows-3 with The objective of the Cosmicflows program is to 17669 galaxies (Tully et al. 2016). This project map the distribution of matter and flows in the lo- has its foundations built on earlier works; The cal universe, understand the motion of our galaxy Nearby Galaxies Atlas (Tully & Fisher 1987) is a with respect to the CMB, and provide new insights first cartography of the three dimensonal struc- in cosmology by providing near-field measurement ture of the Local Universe within redshifts of of basic parameters such as the Hubble Constant. 3000 km/s, in association with the data docu- The fundamental ingredients of this program are mented in the Nearby Galaxies Catalog (Tully the measurements of peculiar velocities of galaxies, 1988). This Atlas highlights the location of our that is their deviation with respect to the Hubble galaxy on the periphery of the Local Void. The expansion. These peculiar velocities of galaxies distribution of galaxies is dominated by the pres- serve as sensors of the source gravitational field, ence of the Virgo cluster. Then, using the union including dark matter. The Cosmicflows program of Abell and Abell-Corwin-Olowin catalogs of rich has three critical constituents: observations, theo- clusters, a cartography of structures extending to retical modeling, and visualizations. Each of these 30,000 km/s was published by Tully et al. (1992). is state-of-the art. Maps of the distribution of superclusters are pro- vided in the plane of the Supergalactic Equator On the observational side, the measurement of that host the Great Attractor, the Great Wall, accurate distances to galaxies permits the separa- the Shapley Concentration, the Pisces-Cetus Su- tion of deviant motions from the cosmic expansion percluster (Figure 4 in Tully et al. 1992). Maps (Tully et al. 2008, Tully et al. 2013, Tully et al. of orthogonal slices display the structure at higher 2016). Our program has accumulated, by far, the SGZ altitudes with the Hercules, Corona-Borealis largest and most coherent assembly of galaxy dis- and Aquarius-Capricornus superclusters, and at tances. lower SGZ altitudes with the Lepus, Horologium- The translation of measured radial velocities Reticulum and Sextans superclusters (Figures 3 with substantial errors into a three-dimensional 2 map of galaxy motions is accomplished with a of strategic importance in the field of cosmogra- Wiener Filter technique averaging multiple real- phy: visualization of scalar fields, vector fields and izations constrained in a Bayesian analysis by the clouds of points. data and an assumed power spectrum of initial The SDvision widget interface provides a multi- density fluctuations (Zaroubi et al. 1999, Hoff- tude of tools to generate visual objects and act on man 2009, Courtois et al. 2012, Doumler et al. their properties. Built around a main view win- 2013). The analysis gives, in addition to the 3-D dow where rotations, translations and scaling can velocity field, the density and potential fields, and be obtained by mouse click-and-drag actions, the the velocity field can be separated into local and widget provides facilities relevant to cosmography tidal components. The shear of the velocity field such as sliders allowing on-the-fly geometrical cuts at each position defines eigenvectors and eigenval- on the galaxy catalog on display. The widget in- ues of the V-web, descriptors of whether the loca- terface can be seen in Figure 1 in the context of tion is in a knot, filament, sheet, or void (Hoffman the visualization of scalar fields. Here, the user et al. 2012). The analysis leads to the identifi- is presented with a histogram. The user can click cation of all the important basins of gravitational interactively on this histogram, an action that will attraction and repulsion. result in the computation and updated visualiza- It is the role of the visualizations to clarify tion of the corresponding isosurface. This inter- the interplay between these various components active facility is most useful for the exploration of in quite complicated circumstances. Cartography complex scalar fields, especially when coupled to has played a seminal role in the development of the 3D navigation possibilities. The widget inter- our current understanding. With new data sets, face can also be seen in Figure 2 in the context already arriving and projected, the visualization of the visualization of a catalog of galaxies. A challenges are multiplying. geometrical filtering is obtained by action on the sliders labelled xmin, xmax, ymin, ymax, zmin, 3. The SDvision visualization software zmax. Among the ∼ 315; 000 galaxies of the cat- alog, ∼ 33; 000 are selected after applying these The SDvision (Saclay Data Visualization) soft- cuts. ware is deployed in the IDL \Interactive Data Lan- Scalar fields, such as density or temperature guage" platform (Pomar`edeet al. 2008). Origi- fields, are visualized by the means of three com- nally developed in the context of the COAST plementary techniques: 1) Ray-casting volume \Computational Astrophysics" Project for the vi- rendering.