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Depth dependence of permeability in the Oregon Cascades inferred from hydrogeologic, thermal, seismic, and magmatic modeling constraints
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95118/1/jgrb14016.pd
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&
Search for exoplanets with the radial-velocity technique: quantitative diagnostics of stellar activity
Aims: Stellar activity may complicate the analysis of high-precision
radial-velocity spectroscopic data when looking for exoplanets signatures. We
aim at quantifying the impact of stellar spots on stars with various spectral
types and rotational velocities and comparing the simulations with data
obtained with the HARPS spectrograph. Methods: We have developed detailed
simulations of stellar spots and estimated their effects on a number of
observables commonly used in the analysis of radial-velocity data when looking
for extrasolar planets, such as radial-velocity curves, cross-correlation
functions, bisector spans and photometric curves. The computed stellar spectra
are then analyzed in the same way as when searching for exoplanets. Results: 1)
A first grid of simulation results is built for F-K type stars, with different
stellar and spot properties. 2) It is shown quantitatively that star spots with
typical sizes of 1% can mimic both radial-velocity curves and the bisector
behavior of short-period giant planets around G-K type stars with a vsini lower
than the spectrograph resolution. For stars with intermediate vsini, smaller
spots may produce similar features. In these cases, additional observables
(e.g., photometry, spectroscopic diagnostics) are mandatory to confirm the
presence of short-period planets. We show that, in some cases, photometric
variations may not be enough to clearly rule out spots as explanations of the
observed radial-velocity variations. This is particularly important when
searching for super-Earth planets. 3) It is also stressed that quantitative
values obtained for radial-velocity and bisector span amplitudes depend
strongly on the detailed star properties, on the spectrograph used, on the set
of lines used, and on the way they are measured.Comment: 12 pages, 16 figures, accepted for publication in A&
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&
The supercluster--void network III. The correlation function as a geometrical statistic
We investigate properties of the correlation function of clusters of galaxies
using geometrical models. On small scales the correlation function depends on
the shape and the size of superclusters. On large scales it describes the
geometry of the distribution of superclusters. If superclusters are distributed
randomly then the correlation function on large scales is featureless. If
superclusters and voids have a tendency to form a regular lattice then the
correlation function on large scales has quasi-regularly spaced maxima and
minima of decaying amplitude; i.e., it is oscillating. The period of
oscillations is equal to the step size of the grid of the lattice.
We calculate the power spectrum for our models and compare the geometrical
information of the correlation function with other statistics. We find that
geometric properties (the regularity of the distribution of clusters on large
scales) are better quantified by the correlation function. We also analyse
errors in the correlation function and the power spectrum by generating random
realizations of models and finding the scatter of these realizations.Comment: MNRAS LaTex style, 12 pages, 7 PostScript figures embedded, accepted
by MNRA
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