1,341 research outputs found
Alignment of galaxies relative to their local environment in SDSS-DR8
We study the alignment of galaxies relative to their local environment in
SDSS-DR8 and, using these data, we discuss evolution scenarios for different
types of galaxies. We defined a vector field of the direction of anisotropy of
the local environment of galaxies. We summed the unit direction vectors of all
close neighbours of a given galaxy in a particular way to estimate this field.
We found the alignment angles between the spin axes of disc galaxies, or the
minor axes of elliptical galaxies, and the direction of anisotropy. The
distributions of cosines of these angles are compared to the random
distributions to analyse the alignment of galaxies. Sab galaxies show
perpendicular alignment relative to the direction of anisotropy in a sparse
environment, for single galaxies and galaxies of low luminosity. Most of the
parallel alignment of Scd galaxies comes from dense regions, from 2...3 member
groups and from galaxies with low luminosity. The perpendicular alignment of S0
galaxies does not depend strongly on environmental density nor luminosity; it
is detected for single and 2...3 member group galaxies, and for main galaxies
of 4...10 member groups. The perpendicular alignment of elliptical galaxies is
clearly detected for single galaxies and for members of < 11 member groups; the
alignment increases with environmental density and luminosity. We confirm the
existence of fossil tidally induced alignment of Sab galaxies at low z. The
alignment of Scd galaxies can be explained via the infall of matter to
filaments. S0 galaxies may have encountered relatively massive mergers along
the direction of anisotropy. Major mergers along this direction can explain the
alignment of elliptical galaxies. Less massive, but repeated mergers are
possibly responsible for the formation of elliptical galaxies in sparser areas
and for less luminous elliptical galaxies.Comment: 15 pages, 15 figures, accepted for publication in A&
Galaxy filaments as pearl necklaces
Context. Galaxies in the Universe form chains (filaments) that connect groups
and clusters of galaxies. The filamentary network includes nearly half of the
galaxies and is visually the most striking feature in cosmological maps.
Aims. We study the distribution of galaxies along the filamentary network,
trying to find specific patterns and regularities.
Methods. Galaxy filaments are defined by the Bisous model, a marked point
process with interactions. We use the two-point correlation function and the
Rayleigh Z-squared statistic to study how galaxies and galaxy groups are
distributed along the filaments.
Results. We show that galaxies and groups are not uniformly distributed along
filaments, but tend to form a regular pattern. The characteristic length of the
pattern is around 7 Mpc/h. A slightly smaller characteristic length 4 Mpc/h can
also be found, using the Z-squared statistic.
Conclusions. We find that galaxy filaments in the Universe are like pearl
necklaces, where the pearls are galaxy groups distributed more or less
regularly along the filaments. We propose that this well defined characteristic
scale could be used to test various cosmological models and to probe
environmental effects on the formation and evolution of galaxies.Comment: 8 pages, 9 figures, 1 table, accepted for publication in A&
Exciton coherence lifetimes from electronic structure
We model the coherent energy transfer of an electronic excitation within
covalently linked aromatic homodimers from first-principles, to answer whether
the usual models of the bath calculated via detailed electronic structure
calculations can reproduce the key dynamics. For these systems the timescales
of coherent transport are experimentally known from time-dependent polarization
anisotropy measurements, and so we can directly assess the whether current
techniques might be predictive for this phenomenon. Two choices of electronic
basis states are investigated, and their relative merits discussed regarding
the predictions of the perturbative model. The coupling of the electronic
degrees of freedom to the nuclear degrees of freedom is calculated rather than
assumed, and the fluorescence anisotropy decay is directly reproduced.
Surprisingly we find that although TDDFT absolute energies are routinely in
error by orders of magnitude more than the coupling energy, the coherent
transport properties of these dimers can be semi-quantitatively reproduced from
first-principles. The directions which must be pursued to yield predictive and
reliable prediction of coherent transport are suggested.Comment: 22 pages, 7 figure
Discovery of a massive supercluster system at
Superclusters are the largest relatively isolated systems in the cosmic web.
Using the SDSS BOSS survey we search for the largest superclusters in the
redshift range .
We generate a luminosity-density field smoothed over
to detect the large-scale over-density regions. Each individual over-density
region is defined as single supercluster in the survey. We define the
superclusters in the way that they are comparable with the superclusters found
in the SDSS main survey.
We found a system we call the BOSS Great Wall (BGW), which consists of two
walls with diameters 186 and 173 Mpc, and two other major superclusters
with diameters of 64 and 91 Mpc. As a whole, this system consists of
830 galaxies with the mean redshift 0.47. We estimate the total mass to be
approximately . The morphology of the
superclusters in the BGW system is similar to the morphology of the
superclusters in the Sloan Great Wall region.
The BGW is one of the most extended and massive system of superclusters yet
found in the Universe.Comment: 4 pages, accepted as a letter in A&
Disentangling Instrumental Features of the 130 GeV Fermi Line
We study the instrumental features of photons from the peak observed at
GeV in the spectrum of Fermi-LAT data. We use the {\sc sPlots}
algorithm to reconstruct -- seperately for the photons in the peak and for
background photons -- the distributions of incident angles, the recorded time,
features of the spacecraft position, the zenith angles, the conversion type and
details of the energy and direction reconstruction. The presence of a striking
feature or cluster in such a variable would suggest an instrumental cause for
the peak. In the publically available data, we find several suggestive features
which may inform further studies by instrumental experts, though the size of
the signal sample is too small to draw statistically significant conclusions.Comment: 9 pages, 22 figures; this version includes additional variables,
study of stat sensitivity, and modification to the chi-sq calculatio
Serologisch onderzoek bij Fusarium oxysporum
Rabbits were immunized with different preparations of F. oxysporum.Antibodies against culture fluid, homogenized mycelium, mycelial extracts and microconidial suspensions reacted in precipitin tests with both culture fluids and mycelium extracts.Cross reactions between formae speciales were very common. The gel diffusion precipitin test proved most suitable to differentiate formae speciales . Most sera did not specifically differentiate formae speciales . However some reacted highly specifically.Concerning the character of the antigens it was concluded that the mycelium contained glycoproteins. The glycoproteins split up into polysaccharides and various proteins both during autolysis in the cultures and during extraction of the mycelium.Rabbits only produced antibodies against proteins after injection with culture liquids or with saline extracts of mycelium. These proteins varied widely in physical properties and it was very difficult to reproduce the same proteins, even by the same extraction procedure. The polysaccharides were much more stablebut antibodies against them could be obtained only by immunization with microconidia. Probably these polysaccharides were present on the surface of the cell wall of the microconidia.The study demonstrated that the polysaccharides from the glycoproteins of Fusarium oxysporum were haptens
Flux- and volume-limited groups/clusters for the SDSS galaxies: catalogues and mass estimation
We provide flux-limited and volume-limited galaxy group and cluster
catalogues, based on the spectroscopic sample of the SDSS data release 10
galaxies. We used a modified friends-of-friends (FoF) method with a variable
linking length in the transverse and radial directions to identify as many
realistic groups as possible. The flux-limited catalogue incorporates galaxies
down to m_r = 17.77 mag. It includes 588193 galaxies and 82458 groups. The
volume-limited catalogues are complete for absolute magnitudes down to M_r =
-18.0, -18.5, -19.0, -19.5, -20.0, -20.5, and -21.0; the completeness is
achieved within different spatial volumes, respectively. Our analysis shows
that flux-limited and volume-limited group samples are well compatible to each
other, especially for the larger groups/clusters. Dynamical mass estimates,
based on radial velocity dispersions and group extent in the sky, are added to
the extracted groups. The catalogues can be accessed via http://cosmodb.to.ee
and the Strasbourg Astronomical Data Center (CDS).Comment: 16 pages, 18 figures, 2 tables, accepted for publication in A&
- …