The Local Void is Really Empty

Are voids in the distribution of galaxies only places with reduced matter density and low star formation efficiency or are they empty of matter? There is now compelling evidence of expansion away from the Local Void at very high velocities. The motion is most reasonably interpreted as an evacuation of the void, which requires that the void be very large and very empty.Comment: Proceedings IAU Symp. 244: Dark Galaxies and Lost Baryons. Cardiff, 25-29 June, 2007. 6 pages, 5 figure

Light on Dark Matter

Galaxies are lighthouses that sit atop peaks in the density field. There is good observational evidence that these lighthouses do not provide a uniform description of the distribution of dark matter.Comment: 4 pages, 5 figures. Paper presented at workshop `Structure and Dynamics in the Local Universe' 24-26 November, 2003, Sydney, Australi

The faint end of the galaxy luminosity function

We present and discuss optical measurements of the faint end of the galaxy luminosity function down to M_R = -10 in five different local environments of varying galaxy density and morphological content. The environments we studied, in order of decreasing galaxy density, are the Virgo Cluster, the NGC 1407 Group, the Coma I Group, the Leo Group and the NGC 1023 Group. Our results come from a deep wide-angle survey with the NAOJ Subaru 8 m Telescope on Mauna Kea and are sensitive down to very faint surface-brightness levels. Galaxies were identified as group or cluster members on the basis of their surface brightness and morphology. The faintest galaxies in our sample have R ~ 22.5. There were thousands of fainter galaxies but we cannot distinguish cluster members from background galaxies at these faint limits so do not attempt to determine a luminosity function fainter than M_R = -10. In all cases, there are far fewer dwarfs than the numbers of low mass halos anticipated by cold dark matter theory. The mean logarithmic slope of the luminosity function between M_R = -18 and M_R = -10 is alpha ~ -1.2, far shallower than the cold dark matter mass function slope of alpha ~ -1.8. We would therefore need to be missing about 90 per cent of the dwarfs at the faint end of our sample in all the environments we study to achieve consistency with CDM theory.Comment: 23 pages, 26 figs, MNRAS in pres

Galaxies: Lighthouses in the Shoals of Dark Halos

It is anticipated from hierarchical clustering theory that there are scaling relationships between halos over a wide range of mass. Observationally it can be difficult to identify the markers that characterize these relationships because of the small numbers of visible probes and confusion from contaminants in projection. Nonetheless, in favorable circumstances it is possible to identify a very useful marker: the radius of the caustic at second turnaround. In a few favorable circumstances it is possible to identify the radius of first turnaround, or zero velocity surface about a collapsed region. It will be shown that specifically the radius of second turnaround scales as anticipated over three orders of magnitude in mass from 10^12 to 10^15 M_sun. Halos are characterized by zones of dispersed velocities within the second turnaround caustic and zones of infall between the first and second turnaround radii. The inner zone is populated in the majority by gas poor morphologies and the outer zone is populated in the majority by gas rich morphologies. The numbers of dwarfs within the inner zone is roughly constant per unit halo mass.Comment: 14 pages, 9 figures. `Galaxies and their Masks: Honoring Ken Freeman's 70th Birthday. 12-16 April, 2010, Sossusvlei, Namibi

The Cosmological Mean Density and its Local Variations Probed by Peculiar Velocities

Peculiar velocities thoughout the region of the local supercluster are reconstructed by two different orbit-retracing methods. The requirement of the optimal correlation between the radial components of reconstructed velocities and the observed peculiar velocities derived from our extensive new catalog of distances puts stringent constraints on the values of the cosmological parameters. Our constraints intersect those from studies of microwave background fluctuations and statistical properties of galaxy clustering: the ensemble of constraints are consistent with Omega_m=0.22\pm 0.02. While motions throughout the Local Supercluster provide a measure of the mean ratio of mass to light, there can be large local fluctuations. Our reconstruction of the infall velocities in the immediate vicinity of the Virgo Cluster shows that there is a mass-to-light anomaly of a factor of 3 to 6 between groups in the general field environment and the heavily populated Virgo Cluster.Comment: 4 pages, 2 figures, version to appear in Astrophysical Journal Letter

Fast Mars communication geometry program

Computer program calculates trajectories of orbiting spacecraft and lander vehicles simultaneously. Using data from both vehicles, program calculates communications geometry which consists of orbiting spacecraft cone/clock angle, lander cone/clock angle, range, range rate and acceleration, and fade, reflective, and system margins