8,068 research outputs found
The Correlation Between Galaxy HI Linewidths and K' Luminosities
The relationship between galaxy luminosities and rotation rates is studied
with total luminosities in the K' band. Extinction problems are essentially
eliminated at this band centered at 2.1 micron. A template luminosity-linewidth
relation is derived based on 65 galaxies drawn from two magnitude-limited
cluster samples. The zero-point is determined using 4 galaxies with accurately
known distances. The calibration is applied to give the distance to the Pisces
Cluster (60 Mpc) at a redshift in the CMB frame of 4771 km/s. The resultant
value of the Hubble Constant is 81 km/s/Mpc. The largest sources of uncertainty
arises from the small number of zero-point calibrators at this time at K' and
present application to only one cluster.Comment: 13 pages including 5 figures and 2 tables. Accepted for publication
in Astrophysical Journa
Quantifying the value of problem structuring interventions?
We review the current work on measuring and evaluating PSM interventions and return to the paradox of trying to determine a specific monetary value. In an attempt to resolve the paradox, we have borrowed freely from economic theory and constructed a scenario where the question of value can be investigated through the effect that a problem structuring intervention will have on information asymmetry in contract formation. This suggests an avenue of research where the value of problem structuring interventions can be investigated empirically. We discuss the difficulties of research design to investigate this question but also the potential benefits.European Commissio
Internal kinematics of spiral galaxies in distant clusters. Part II. Observations and data analysis
We have conducted an observing campaign with FORS at the ESO-VLT to explore
the kinematical properties of spiral galaxies in distant galaxy clusters. Our
main goal is to analyse transformation- and interaction processes of disk
galaxies within the special environment of clusters as compared to the
hierarchical evolution of galaxies in the field. Spatially resolved MOS-spectra
have been obtained for seven galaxy clusters at 0.3<z<0.6 to measure rotation
velocities of cluster members. For three of the clusters, Cl0303+17, Cl0413-65,
and MS1008-12, for which we presented results including a TF-diagram in Ziegler
et al. 2003, we describe here in detail the observations and data analysis.
Each of them was observed with two setups of the standard FORS MOS-unit.With
typical exposure times of >2 hours we reach an S/N>5 in the emission lines
appropriate for the deduction of the galaxies' internal rotation velocities
from [OII], Hbeta, or [OIII] profiles. Preselection of targets was done on the
basis of available redshifts as well as from photometric and morphological
information gathered from own observations, archive data, and from the
literature. Emphasis was laid on the definition of suitable setups to avoid the
typical restrictions of the standard MOS unit for this kind of observations. In
total we assembled spectra of 116 objects of which 50 turned out to be cluster
members. Position velocity diagrams, finding charts as well as tables with
photometric, spectral, and structural parameters of individual galaxies are
presented.Comment: 18 pages, 6 figures, accepted for publication in Astronomy and
Astrophysics. A version with full resolution figures can be downloaded from
http://www.uni-sw.gwdg.de/~vwgroup/publications.htm
Elucidating glycosaminoglycan–protein–protein interactions using carbohydrate microarray and computational approaches
Glycosaminoglycan polysaccharides play critical roles in many cellular processes, ranging from viral invasion and angiogenesis to spinal cord injury. Their diverse biological activities are derived from an ability to regulate a remarkable number of proteins. However, few methods exist for the rapid identification of glycosaminoglycan–protein interactions and for studying the potential of glycosaminoglycans to assemble multimeric protein complexes. Here, we report a multidisciplinary approach that combines new carbohydrate microarray and computational modeling methodologies to elucidate glycosaminoglycan–protein interactions. The approach was validated through the study of known protein partners for heparan and chondroitin sulfate, including fibroblast growth factor 2 (FGF2) and its receptor FGFR1, the malarial protein VAR2CSA, and tumor necrosis factor-α (TNF-α). We also applied the approach to identify previously undescribed interactions between a specific sulfated epitope on chondroitin sulfate, CS-E, and the neurotrophins, a critical family of growth factors involved in the development, maintenance, and survival of the vertebrate nervous system. Our studies show for the first time that CS is capable of assembling multimeric signaling complexes and modulating neurotrophin signaling pathways. In addition, we identify a contiguous CS-E-binding site by computational modeling that suggests a potential mechanism to explain how CS may promote neurotrophin-tyrosine receptor kinase (Trk) complex formation and neurotrophin signaling. Together, our combined microarray and computational modeling methodologies provide a general, facile means to identify new glycosaminoglycan–protein–protein interactions, as well as a molecular-level understanding of those complexes
UGC 7388: a galaxy with two tidal loops
We present the results of spectroscopic and morphological studies of the
galaxy UGC7388 with the 8.1-m Gemini North telescope. Judging by its observed
characteristics, UGC7388 is a giant late-type spiral galaxy seen almost
edge-on. The main body of the galaxy is surrounded by two faint (\mu(B) ~ 24
and \mu(B) ~ 25.5) extended (~20-30 kpc) loop-like structures. A large-scale
rotation of the brighter loop about the main galaxy has been detected. We
discuss the assumption that the tidal disruption of a relatively massive
companion is observed in the case of UGC7388. A detailed study and modeling of
the observed structure of this unique galaxy can give important information
about the influence of the absorption of massive companions on the galactic
disks and about the structure of the dark halo around UGC7388.Comment: 8 pages, 5 figure
A warped disk model for M33 and the 21-cm line width in spiral galaxies
To determine the actual HI distribution and the velocity field in the
outermost disk of the spiral galaxy M33, a tilted-ring model is fitted to 21-cm
line data taken with the Arecibo Telescope. Since M33 is one of the main
calibrators for the extragalactic distance scale derived through the
Tully-Fisher relation, the outer disk warping is of interest for a correct
determination and deprojection of the galaxy's line width. Even though our best
model predicts small effects on the observed line width of M33, we show that
similar outer disk warping in galaxies oriented differently along our line of
sight could affect the widths considerably. Therefore there may be systematic
effects in the determination of the rotation velocities and dynamic masses of
spiral galaxies, whose exact value depends also on which method is used for
measuring the galaxy's total line width.Comment: 27 pages, ps files only, ApJ in pres
A List of Galaxies for Gravitational Wave Searches
We present a list of galaxies within 100 Mpc, which we call the Gravitational
Wave Galaxy Catalogue (GWGC), that is currently being used in follow-up
searches of electromagnetic counterparts from gravitational wave searches. Due
to the time constraints of rapid follow-up, a locally available catalogue of
reduced, homogenized data is required. To achieve this we used four existing
catalogues: an updated version of the Tully Nearby Galaxy Catalog, the Catalog
of Neighboring Galaxies, the V8k catalogue and HyperLEDA. The GWGC contains
information on sky position, distance, blue magnitude, major and minor
diameters, position angle, and galaxy type for 53,255 galaxies. Errors on these
quantities are either taken directly from the literature or estimated based on
our understanding of the uncertainties associated with the measurement method.
By using the PGC numbering system developed for HyperLEDA, the catalogue has a
reduced level of degeneracies compared to catalogues with a similar purpose and
is easily updated. We also include 150 Milky Way globular clusters. Finally, we
compare the GWGC to previously used catalogues, and find the GWGC to be more
complete within 100 Mpc due to our use of more up-to-date input catalogues and
the fact that we have not made a blue luminosity cut.Comment: Accepted for publication in Classical and Quantum Gravity, 13 pages,
7 figure
Mixing Quantum and Classical Mechanics
Using a group theoretical approach we derive an equation of motion for a
mixed quantum-classical system. The quantum-classical bracket entering the
equation preserves the Lie algebra structure of quantum and classical
mechanics: The bracket is antisymmetric and satisfies the Jacobi identity, and,
therefore, leads to a natural description of interaction between quantum and
classical degrees of freedom. We apply the formalism to coupled quantum and
classical oscillators and show how various approximations, such as the
mean-field and the multiconfiguration mean-field approaches, can be obtained
from the quantum-classical equation of motion.Comment: 31 pages, LaTeX2
An Unbiased Estimate of the Global Hubble Constant in the Region of Pisces-Perseus
We obtain an unbiased estimate of the global Hubble constant H0 in the volume
of cz<12000km/s in the region of Pisces-Perseus. The Tully-Fisher (TF) relation
is applied to a magnitude limited sample of 441 spirals selected from the
Arecibo 21cm catalog. The photometry data were calibrated with CCD observations
and we achieve 0.13mag for the photometric internal error. We use a maximum
likelihood method for the TF analysis. Monte-Carlo simulations demonstrate that
our method reproduces a given H0 at the 95% confidence level. By applying the
method to our sample galaxies, we obtain the unbiased global Hubble constant
H0=65+-2(+20,-14) km/s/Mpc; the first and the second terms represent the
internal random error and the external errors, respectively. We also find a
good agreement for our H0 with those recently obtained via Cepheid observation,
the TF relation and supernovae. Hubble velocities of the spirals inferred from
our H0 show no significant systematic difference from those given in the Mark
III catalog. The same analysis for H0 is carried out using r-band photometry
data of the Pisces-Perseus region given by Willick et al.(1997). We obtain a
global H0 which is consistent with that obtained from our B-band analysis. A
bulk motion in the Pisces-Perseus region is briefly discussed, based on our
calibration of H0. Our r-band TF analysis supports the notion of a coherent
streaming motion of the Pisces-Perseus ridge with -200km/s with respect to the
CMB, in agreement with most modern studies.Comment: 40 pages, 27 postscript figures, to appear in Ap.J. Figures are
included in the tex
The Tully-Fisher relation at intermediate redshift
Using the Very Large Telescope in Multi Object Spectroscopy mode, we have
observed a sample of 113 field spiral galaxies in the FORS Deep Field (FDF)
with redshifts in the range 0.1<z<1.0. The galaxies were selected upon apparent
brightness (R<23) and encompass all late spectrophotometric types from Sa to
Sdm/Im. Spatially resolved rotation curves have been extracted for 77 galaxies
and fitted with synthetic velocity fields taking into account all observational
effects from inclination and slit misalignment to seeing and slit width. We
also compared different shapes for the intrinsic rotation curve. To gain robust
values of V_max, our analysis is focussed on galaxies with rotation curves
which extend well into the region of constant rotation velocity at large radii.
If the slope of the local Tully-Fisher relation (TFR) is held fixed, we find
evidence for a mass-dependent luminosity evolution which is as large as up to 2
mag for the lowest-mass galaxies, but is small or even negligible for the
highest-mass systems in our sample. In effect, the TFR slope is shallower at
z~0.5 in comparison to the local sample. We argue for a mass-dependent
evolution of the mass-to-light ratio. An additional population of blue,
low-mass spirals does not seem a very appealing explanation. The flatter tilt
we find for the distant TFR is in contradiction to the predictions of recent
semi-analytic simulations.Comment: 18 pages, 14 figures, A&A, in press. Section on sample completeness
added. Please note that the entire analysis is based on undisturbed, high
quality rotation curves! Potential effects of tidal interactions are also
discusse
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