Figures and Captions
Figure 3-1: Large scale structure in a Dark Matter supercomputer simulation. Image courtesy of the HPCC group at the Univeristy of Washington and George Lake. This simulation shows a void filled Universe with much filamentary structure. Clusters of galaxies appear to form at the intersections of voids.
Figure 3-2: CCD image of Hickson Compact Group 92 taken by the author using the NTT telescope at the ESO observatory. The image shows that much of the group contains diffuse intergalactic light.
Figure 3-3: CCD image of the center of the Coma Cluster, the richest nearby cluster. The center is dominated by many elliptical and SO galaxies.
Figure 3-4: A sample of cluster density profiles showing the variations in the outer fall off. Data come from West and Bothun (1990).
Figure 3-5: Encounter geometry for two stars which gravitationally scatter of off one another.
Figure 3-6: Spatial plot of the position of galaxies in the Zwicky catalog located within 30 degrees of the center of the Coma cluster. Approximately 1900 galaxies are shown here and 200 alone define the Coma cluster. A hint of the Great Wall structure can also be seen in just this positional data.
Figure 3-7: Combined spatial distribution of all catalogued galaxies onto the sphere of the sky defined by Galactic coordinates. The dark band running down the center is the plane of the Milky Way, through which distant galaxies can not be seen. The flattened distribution almost perpendicular to the plane is the Local Supercluster. This Image courtesy of Alan Dressler.
Figure 3-8: Combined Northern and Southern Hemisphere redshift surveys initiated by M. Geller and J. Huchra. These data best define the coherency of structure on rather large scales.
Figure 3-9: A typical absorption line spectrum of a galaxy showing the many absorption lines in the spectrum. The principal lines used for redshift determination are the Calcium H and K lines at wavelength about 3900 angstroms, the Magnesium I complext at 5175 angstroms, and the sodium D lines at 5800 angstroms. Image courtesy of Jeff Willick.
Figure 3-10: An example of hierarchical clustering in the distribution of lights seen in this image of the East Coast of the US taken at night. Image courtesy of NOAA.
Figure 3-11: Large scale structure is seen in the Slice of the Universe first published by de Lapparent \etal (1986). The opening angle of the vertex represents the angular extent of the strip survey and the width in declination has been collapsed. Each galaxy is plotted at its redshift distance from the Earth. Virilized structures, such as the Coma cluster in the center of the image, appear as linear features pointed directly at the observer. This representation of the Large Scale Structure clearly reveals the presence of voids. This representation was originally done by Lars Lindberg Christensen, University of Copenhagen, Denmark.
Figure 3-12: Slice diagrams of a section of the Las Campanas Redshift Survey initiated by Steve Shectman and collaborators (see Da Costa etal 1996). The void filled Universe is quite apparent in this slice and numerous thin walls structures are also evident.
Figure 3-13: The two point correlation function for groups of galaxies. The spatial correlation function is well approximated by the form (s/so)b, where the correlation length so and the slope of the power law, b, are the fitting parameters. The dashed line indicates normalization of the power law fit which defines the correlation length. The spatial scale over which the data cross this line defines so. The Y-axis plots the logarithim of (s/so)b. The fit to a power law for this data gives a slope of -1.3 and a correlation length of 8 -1 Mpc. Adapted from Ramella etal (1989).
Figure 3-14: Cluster-cluster correlation function for an X-ray flux limited sample of galaxies from Bahcall and Cen (1992). The x-axis is the spatial scale, s, in log h-1 Mpc and the Y-axis plots the logarithim of (s/so)b. Although the data set is noisy and the sample size is small, the data are consistent with a correlation length of 21 h-1 Mpc. This is equivalent to the correlation length found in numerical simulation of low density universes (see Bahcall and Cen 1992; Mo \etal 1996).
Figure 3-15: Schematic representation of hubble flow out to 20,000 km/s in which there is a constant 1,000 km/s peculiar velocity perturbation which translates into a percentage distance error. Beyond a velocity of 10,000 km/s uncertainties in distance would produce percentage error estimates larger than those produce from this peculiar velocity perturbation.
Figures 3-16: Distortion of the Velocity Field which is caused by spherically symmetric infall into a virialized structure. Here the spatial distribution of infall galaxies is plotted with heads or tails on them to indicate the amplitude of their infall velocity. Note that the heads and tails always point at the center of the virialized cluster. This figure comes from Villumsen and Davis (1986).
Figure 3-17: Schematic representation of the Local Velocity Field from Aaronson \etal (1986). Here the Milky Way is infalling towards Virgo at approximately 300 km/s and the entire local Supercluster is infalling towards Hydra-Cen at approximately 300 km/s. The vector sum of these two infall components to the motion of the Milky Way approximately accounts for the observed dipole anisotropy in the CMB.
Figure 3-18: Individual galaxy peculiar velocities plotted in comparison with the spherically symmetric infall model that would be generated by a Great Attractor located at kinematic distance of 4350 km/s from the Milky Way. The solid curved lines define the front-side and back-side caustic infall surfaces and the dashed lines represent 1-sigma error surfaces. The solid vertical lines represent rt for the Great Attractor. The letter A denotes the Antlia cluster. The model has been normalized such that the Great Attractor accounts for the entire observed dipole anisotropy in the CMB. Figure adapted from Figure 4 in Bothun \etal (1992a).
Figure 3-19: Cone diagram for all known velocities that are in the putative Great Attractor region of the sky. The large "finger" which is seen is the Centaurus cluster.
Figure 3-20: Distribution of known peculiar velocities for nearby groups and clusters as projected on the plane of the Local Supercluster. Nominal distances are in km/s and the amplitude and direction of any measured peculiar velocity is indicated by the arrows that are tagged onto some groups and clusters. Figure adapted from Mould \etal (1993).
Figure 3-21: Structure of the large void seen in the first CFA Slice data in redshift space. Adapted from Bothun \etal (1992).
Figure 3-22: Peculiar velocity data from Giovanelli \etal (1996) whose sample shows that the average peculiar velocity declines to zero at observed redshift of 6000 km/s. This behavior is inconsistent with the Lauer and Postman (1994) result indicated by the +689 constant velocity line. The numbers below each data bin mark the number of galaxies in the sample.
Figure 3-23: Deviations from a uniform Hubble flow compiled by Mould (1996). Solid circles: clusters of galaxies with Tully-Fisher distances. Solid triangles: EPM data of Schmidt et al. (1994). Open symbols: brightest cluster members from Lauer & Postman (1994). There is no evidence that a significantly different value of the Hubble Constant pertains for samples located inside and outside the distance of the Coma cluster at v = 7200 km/sec. Moreover, it is clear that beyond 5000 km/s, the noise in determining Ho has greatly diminished. Note the considerable scatter in the Lauer and Postman sample.