21 research outputs found
Seeking the Local Convergence Depth. IV. Tully-Fisher Observations of 35 Abell Clusters
We present Tully-Fisher observations for 35 rich Abell clusters of galaxies.
Results from I band photometry and optical rotation curve work comprise the
bulk of this paper. This is the third such data installment of an all-sky
survey of 52 clusters in the distance range 50 to 200\h Mpc. The complete data
set provides the basis for determining an accurate Tully-Fisher template
relation and for estimating the amplitude and direction of the local bulk flow
on a 100\h Mpc scale.Comment: 18 pages, 21 figures, uses AAS LaTeX; to appear in the Astronomical
Journa
Seeking the Local Convergence Depth. V. Tully-Fisher Peculiar Velocities for 52 Abell Clusters
We have obtained I band Tully-Fisher (TF) measurements for 522 late-type
galaxies in the fields of 52 rich Abell clusters distributed throughout the sky
between 50 and 200\h Mpc. Here we estimate corrections to the data for various
forms of observational bias, most notably Malmquist and cluster population
incompleteness bias. The bias-corrected data are applied to the construction of
an I band TF template, resulting in a relation with a dispersion of 0.38
magnitudes and a kinematical zero-point accurate to 0.02 magnitudes. This
represents the most accurate TF template relation currently available.
Individual cluster TF relations are referred to the average template relation
to compute cluster peculiar motions. The line-of-sight dispersion in the
peculiar motions is 341+/-93 km/s, in general agreement with that found for the
cluster sample of Giovanelli and coworkers.Comment: 31 pages, 14 figures, uses AAS LaTeX; to appear in the Astronomical
Journa
The X-ray Cluster Dipole
We estimate the dipole of the whole sky X-ray flux-limited sample of
Abell/ACO clusters (XBACs) and compare it to the optical Abell/ACO cluster
dipole. The X-ray cluster dipole is well aligned () with the
CMB dipole, while it follows closely the radial profile of its optical cluster
counterpart although its amplitude is per cent lower. In view of
the fact that the the XBACs sample is not affected by the volume incompleteness
and the projection effects that are known to exist at some level in the optical
parent Abell/ACO cluster catalogue, our present results confirm the previous
optical cluster dipole analysis that there are significant contributions to the
Local Group motion from large distances (Mpc). In order to
assess the expected contribution to the X-ray cluster dipole from a purely
X-ray selected sample we compare the dipoles of the XBACs and the Brightest
Cluster Sample (Ebeling et al. 1997a) in their overlap region. The resulting
dipoles are in mutual good aggreement with an indication that the XBACs sample
slightly underestimates the full X-ray dipole (by per cent) while the
Virgo cluster contributes about 10 - 15 per cent to the overall X-ray cluster
dipole. Using linear perturbation theory to relate the X-ray cluster dipole to
the Local group peculiar velocity we estimate the density parameter to be
.Comment: 16 pages, latex, + 4 ps figures, submitted to Ap
Structural probing of the HIV-1 polypurine tract RNA:DNA hybrid using classic nucleic acid ligands
The interactions of archetypical nucleic acid ligands with the HIV-1 polypurine tract (PPT) RNA:DNA hybrid, as well as analogous DNA:DNA, RNA:RNA and swapped hybrid substrates, were used to probe structural features of the PPT that contribute to its specific recognition and processing by reverse transcriptase (RT). Results from intercalative and groove-binding ligands indicate that the wild-type PPT hybrid does not contain any strikingly unique groove geometries and/or stacking arrangements that might contribute to the specificity of its interaction with RT. In contrast, neomycin bound preferentially and selectively to the PPT near the 5′(rA)4:(dT)4 tract and the 3′ PPT-U3 junction. Nuclear magnetic resonance data from a complex between HIV-1 RT and the PPT indicate RT contacts within the same regions highlighted on the PPT by neomycin. These observations, together with the fact that the sites are correctly spaced to allow interaction with residues in the ribonuclease H (RNase H) active site and thumb subdomain of the p66 RT subunit, suggest that despite the long cleft employed by RT to make contact with nucleic acids substrates, these sites provide discrete binding units working in concert to determine not only specific PPT recognition, but also its orientation on the hybrid structure
The Dipole Anisotropy of the First All-Sky X-ray Cluster Sample
We combine the recently published CIZA galaxy cluster catalogue with the
XBACs cluster sample to produce the first all-sky catalogue of X-ray clusters
in order to examine the origins of the Local Group's peculiar velocity without
the use of reconstruction methods to fill the traditional Zone of Avoidance.
The advantages of this approach are (i) X-ray emitting clusters tend to trace
the deepest potential wells and therefore have the greatest effect on the
dynamics of the Local Group and (ii) our all-sky sample provides data for
nearly a quarter of the sky that is largely incomplete in optical cluster
catalogues. We find that the direction of the Local Group's peculiar velocity
is well aligned with the CMB as early as the Great Attractor region 40 h^-1 Mpc
away, but that the amplitude of its dipole motion is largely set between 140
and 160 h^-1 Mpc. Unlike previous studies using galaxy samples, we find that
without Virgo included, roughly ~70% of our dipole signal comes from mass
concentrations at large distances (>60 h^-1 Mpc) and does not flatten,
indicating isotropy in the cluster distribution, until at least 160 h^-1 Mpc.
We also present a detailed discussion of our dipole profile, linking observed
features to the structures and superclusters that produce them. We find that
most of the dipole signal can be attributed to the Shapley supercluster
centered at about 150 h^-1 Mpc and a handful of very massive individual
clusters, some of which are newly discovered and lie well in the Zone of
Avoidance.Comment: 15 Pages, 9 Figures. Accepted by Ap