Brad K. Gibson

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We present here the Ðnal results of the Hubble Space Telescope (HST ) Key Project to measure the Hubble constant. We summarize our method, the results, and the uncertainties, tabulate our revised distances, and give the implications of these results for cosmology. Our results are based on a Cepheid calibration of several secondary distance methods applied(More)
The use of spatial relational terms requires the selection of a reference frame and the construction of a spatial template. The reference frame divides up space, indicating above/below, front/ back, and left/right directions. Spatial templates are applied to reference frames and define regions in space that correspond to good, acceptable, and bad uses of(More)
Age-related neurodegenerative disease has been mechanistically linked with mitochondrial dysfunction via damage from reactive oxygen species produced within the cell. We determined whether increased mitochondrial oxidative stress could modulate or regulate two of the key neurochemical hallmarks of Alzheimer's disease (AD): tau phosphorylation, and(More)
We modeled the evolution of the Milky Way Galaxy to trace the distribution in space and time of four prerequisites for complex life: the presence of a host star, enough heavy elements to form terrestrial planets, sufficient time for biological evolution, and an environment free of life-extinguishing supernovae. We identified the Galactic habitable zone(More)
Contrary to several recent studies, we find strong evidence in the Sloan Digital Sky Survey for the “Holmberg Effect”, the tendency for the satellites of isolated late-type galaxies to align with the minor axis of the galactic disc. In the case of isolated earlytypes, we find that satellites tend to align with the major axis of the galaxy. Using mock(More)
We present the white dwarf sequence of the globular cluster M4, based on a 123 orbit Hubble Space Telescope exposure, with limiting magnitude V∼ 30, I∼ 28. The white dwarf luminosity function rises sharply for I> 25.5, consistent with the behaviour expected for a burst population. The white dwarfs of M4 extend to approximately 2.5 magnitudes fainter than(More)
Seven cosmological hydrodynamic simulations of disk galaxy formation are analyzed to determine the alignment of the disk within the dark matter halo and the internal structure of the halo. We find that the orientation of the outer halo, beyond ∼ 0.1 rvir, is unaffected by the presence of the disk. In contrast, the inner halo is aligned such that the halo(More)
We explore the dependence of the radial alignment of subhalos on the mass of the host halo they orbit in. As the effect is seen on a broad range of scales including massive clusters as well as galactic systems it only appears natural to explore this phenomenon by means of cosmological simulations covering the same range in masses. We have 25 well resolved(More)
We explore the radial alignment of subhalos in 2-dimensional projections of cosmological simulations. While most other recent studies focussed on quantifying the signal utilizing the full 3-dimensional spatial information any comparison to observational data has to be done in projection along random lines-of-sight. We have a suite of well resolved host dark(More)
We re-examine the respective roles played by supernovae (SNe) Types Ia and II in enriching the intracluster medium (ICM) of galaxy clusters, in light of the recent downward shift of the ASCA abundance ratios of α-elements to iron favoured by Ishimaru & Arimoto (1997, PASJ, 49, 1). Because of this shift, Ishimaru & Arimoto conclude that ∼ 50% of the ICM iron(More)